Microbiology Spring Quarter Practice Final (137 qs) [Formatting by Ray, Explanations by Kevin Peng] Compiled 5/18/08 - PowerPoint PPT Presentation

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Microbiology Spring Quarter Practice Final (137 qs) [Formatting by Ray, Explanations by Kevin Peng] Compiled 5/18/08

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Title: Microbiology Spring Quarter Practice Final (137 qs) [Formatting by Ray, Explanations by Kevin Peng] Compiled 5/18/08


1
Microbiology Spring QuarterPractice Final(137
qs)Formatting by Ray, Explanations by Kevin
PengCompiled 5/18/08
2
Intracellular multiplication is characteristic of
infection by which of the following
organismsA) Bacillus anthracis and Legionella
pneumophilaB) Brucella abortus and LIsteria
monocytogenesC) Bordetella pertussis and
Campylobacter jejuniD) Mycoplasma pneumoniae and
Chlamydia psittaciE) Klebsiella pneumoniae and
Neisseria meningitidis
  • The answer is B
  • There is that awesome chart that was printed in
    the winter micro syllabus but never posted online
    that classifies the obligate intracellular
    pathogens. I keep on thinking that Mycoplasma is
    an obligate intracellular pathogen, but it can
    definitely be grown on plates. (Dont worry, the
    explanations get better.)

3
2) The following organism is often transmitted by
infected placentas of affected ruminantsA)
Francisella tularensisB) Yersinia pestisC)
Brucella abortusD) Erlichia sennetsuE) Bacillus
anthracis
  • The answer is C
  • Coxiella burnetti, the cause of Q fever, is a
    zoonosis that is associated with parturition.
    However, Brucella abortus is often transmitted by
    the infected placentas of ruminants. (The
    explanations do get better, I promise.)

4
3) Respiratory Syncitial VirusA) Grows best at
33 CB) requires organ culture for isolationC)
is spread most effectively by fomites and large
particle aerosolsD) is inhibited by the
antiviral drug rimantidineE) has hemagglutinin
and neuraminidase activity on a single envelope
glycoprotein
  • The answer is C
  • Respiratory syncytial virus (family
    Paramyxoviridae, subfamily Pneumovirinae) is the
    most common cause of lower respiratory tract
    infection in children. It has two major
    subgroups, A, and B, classified according to the
    G glycoprotein. The G glycoprotein binds the
    viral receptor the F glycoprotein (which must
    be cleaved by a host cell protease into F1 and F2
    to be active) mediates membrane fusion. (The F
    protein is called HN in mumps subfamily
    Paramyxovirinae, genus Rubulavirus and
    parainfluenza subfamily Paramyxovirinae, genus
    Paramyxovirus because the protein mediates
    hemagglutination and neuraminidase activity.)
  • There is no hemagglutination, hemadsorption, or
    hemolysin activity in RSV.
  • RSV is spread primarily by fomites but also by
    aerosols.
  • Amantadine and rimantadine block influenzaviruss
    M2, preventing acidification of the endosome and
    hence blocking penetration and uncoating of
    influenzavirus.
  • This does not matter for RSV, which fuses with
    host cell membranes at neutral pH (like all
    members of Paramyxoviridae).
  • Answer choice A is probably hinting at
    Rhinovirus, which grows best at 33 deg C and is
    resistant to inactivation at 50 deg C. (In
    contrast, Enterovirus grows best at 37 deg C and
    is inactivated at 50 deg C.) Answer choice b is
    probably also hinting at Rhinovirus, which can be
    grown in vitro in human fetal trachea organ
    culture.

5
4) The most important risk factor for the
development of pyelonephritis isA) the
presence of uropathogenic E.coliB) obstruction
to urine flowC) sexual intercourseD) vaginal
colonization with E.coliE) poor phagocytic
function in the renal medulla
  • The answer is B
  • Pyelonephritis is an infection of the tissue of
    the kidney. The greatest defense against UTI is
    normal urine flow. By the way, the renal medulla
    is an immunological desert (Dr. Savoia) a few
    organisms may be infectious while infections in
    the cortex require 10,000 organisms or more. This
    is partially because the large fluctuations in
    medullary osmolality dont promote phagocytic
    function.

6
5) All of the following statements are true of
syphilis EXCEPTA) the etiologic organism
cannot be cultivated in vitroB) the length of
the incubation period reflects the size of the
initial inoculum.C) immunity to reinfection
develops immediately after primary infectionD)
the disease may be acquired by sexual contact, in
utero, by transfusion, or by direct inoculation
  • The answer is C
  • Treponema pallidum can be cultured only in vivo
    (in a rabbit model). The incubation period is
    indirectly proportional to the size of the
    inoculum. The treatment of choice is parenteral
    penicillin G. Transmission is transplacental, by
    transfusion, by direct inoculation, or by sexual
    contact. Humans are the only natural hosts. Past
    infection with syphilis provides no immunity to
    reinfection after primary infection, about 70
    of patients are positive for anti-treponemal and
    non-treponemal antibody after primary infection
    and 99 are positive after secondary or tertiary
    infection.

7
6) Sam and Janet and their 2 ½ year old daughter,
who is in day care, live near the lagoon in
Carlsbad. Their last vacation was on Cape Cod,
where they hiked, played in a fresh water pond
and ate sushi. They are at risk for all of the
following parasitic diseases EXCEPTA)
anasakiasisB) babesiosisC) giardiasisD)
malariaE) schistosomiasis
  • The answer is E
  • Anasakis is found in sushi. In the US, Babesia is
    found in New England but it is endemic worldwide
    the asplenic and the immunocompromised are
    particularly susceptible. Giardia cysts are hardy
    and can survive for months in cold water
    outbreaks are sometimes associated with daycare
    centers. In the US, malaria was eradicated in the
    1950sI dont get why they are at risk for
    malaria. (explain this to me if you see the
    reason) Schistosoma are blood flukes and they
    are the worms that are paired for life
    heterosexually. Schistosoma are endemic in South
    America, Africa, the Middle East, and China
    cercariae, which are the free-living worm
    released from intermediate host snails into fresh
    water, are infectious.

8
7) Metronidazole is effective against all of the
following EXCEPTA) Bacteriodes fragilisB)
Crytposporidium parvumC) Entameoba
histolyticaD) Giardia lambliaE) Trichomonas
vaginalis
  • The answer is B
  • Cryptosporidium is an opportunistic pathogen
    infection is a zoonosis. Its life cycle is
    similar to that of Plasmodiums (oocysts,
    sporozoites, trophozoites, schizonts, merozoites,
    macro- and microgametes). It differs from the
    other intestinal protozoans because it is,
    strictly, not intracellular. Almost nothing,
    including metronidazole, was active against
    Cryptosporidium until nitazoxanide was developed.
    The target of nitazoxanide is PFOR, which is part
    of an anaerobic pathway shared by Entamoeba,
    Giardia, and Cryptosporidium.

9
8) The pathologic lesion most closely associated
with syphilis isA) abscess formation at the
site of inoculationB) immune complex deposition
along basement membranesC) necrotizing
granulomasD) obliterative endarteritisE) plasma
cell infiltrates
  • The answer is D
  • Syphiliss characteristic pathologic lesion is
    obliterative endarteritis.

10
9) The most common inherited human
immunodeficiencyA) Absent complement factor
8B) absent 47kd neutrophil cytosolic oxidaseC)
block in B cell maturationD) IgA deficiencyE)
IgG deficiency
  • The answer is D
  • The most common inherited human immunodeficiency
    is IgA deficiency.

11
10) All of the following are true of the
cytotoxic T lymphocyte response to HIV
EXCEPTA) it controls viremia during primary
infectionB) it may account for slow destruction
of CD4 cells during the clinically latent
periodC) it is MHC-restrictedD) it is most
potent in the most advanced patientsE) it
targets envelope glycoproteins (GP41 and 120)
  • The answer is D
  • The initial CTL response is probably important
    for limiting viremia. Via their MHC class I, CD8
    cells specifically recognize HIV-infected cells
    and kill them. This can lead to decline in CD4
    count, although CD4 cells also die off simply by
    direct virus-mediated cell deathrecently-infected
    cells undergo apoptosis. CD8 cells target HIV
    proteins, particularly the envelope glycoproteins
    gp41 and gp120.

12
11) Host risk factors for the development of
urinary tract infection include all of the
following EXCEPTA) complement deficiency
involving a component of the membrane attack
complexB) increased number of uroepithelial
receptors for mannose sensitive piliC) diaphragm
useD) benign prostatic hypertrophyE) introital
colonization with enteric organisms
  • The answer is A
  • Terminal complement deficiency predisposes to
    Neisseria sepsis.

13
12) Vancomycin should be administered slowly to
avoidA) Renal failureB) deafnessC) sudden
release of histamine from mast cellsD) feverE)
jaundice
  • The answer is C
  • Red man syndrome is histamine-mediated but is not
    an allergic reaction. Vancomycin is indeed
    ototoxic, but this is not related to rate of
    infusion. It is nephrotoxic only if given in
    conjunction with aminoglycosides. Also, it is
    excreted only by glomerular filtration and must
    be dose-adjusted in renal failure. (Peritoneal
    dialysis and hemodialysis do not remove
    vancomycin.)

14
13) Oral vancomycin is therapeutic for which of
the following?A) methicillin-resistant S.
aureus bacteremiaB) vancomycin-resistant
enterococcal cystitisC) streptococcal
pharyngitisD) pseudomembranous colitisE)
giardiasis
  • The answer is D
  • Vancomycin is given IV in every circumstance
    except for treatment of C. difficile colitis.

15
14) All of the following are true of the HIV
viral load in plasma (HIV RNA copy number)
EXCEPTA) it is measured by monoclonal
antibody, using antigen capture ELISAB) it is
useful in assessing responses to antiretroviral
therapyC) it is expressed in log10 because of
the broad range of possible valuesD) measurement
is feasible at all stages of HIV infectionE) it
has prognostic value
  • The answer is A
  • HIV viral load is usually measured with PCR, not
    monoclonal antibody and ELISA. HIV viral load is
    the best prognostic factor for rate of
    progression of disease and rate of CD4 decline.
    After initial infection, the viral load
    stabilizes and remains at the same level or
    increases slowly in the absence of antiretroviral
    therapy. During successful treatment, viral load
    is often below the limit of detection of the test
    used, and these low levels are associated with
    successful control and lower rates of resistance.

16
15) Which of the following cephalosporins is
substantially excreted by both renal and hepatic
mechanisms?A) cefazolin (Ancef)B) ceftazidime
(Fortaz)C) ceftriaxone (Rocephin)D) cefuroxime
(Ceftin)E) cephalexin (Keflex)
  • The answer is C
  • The cephalosporins are generally excreted by the
    kidney via glomerular filtration and tubular
    secretion, but ceftriaxone, cefotetan, and
    cefoperazone are partially excreted in bile.

17
16) Third generation cephalosporins differ from
first generation cephalosporins in all of the
following EXCEPTA) they are more active
against Enterococcus faeciumB) they are more
active against P. aeruginosaC) they are more
active against K. pneumoniaeD) they are more
active against Enterobacteri aerogeneseE) they
are more active against E.coli
  • The answer is A
  • Cephalosporins have no activity against Listeria
    or the enterococci. With each subsequent
    generation, they are more active against
    Gram-negatives and more resistant to
    ß-lactamases however, they lose activity against
    Gram-positives.

18
17) All of the following are true of imipenem
EXCEPTA) It is excreted by the kidneysB) it
is metabolized by the kidneysC) it is more
likely to cause seizures than is ceftriaxoneD)
it will rapidly destory the normal microbial
flora of the mouth and the colonE) it is
inactivated by the TEM plasmid beta-lactamases
found in N. gonorrhea
  • The answer is E
  • In general, the carbapenems are extremely potent,
    broad-spectrum drugs that will completely wipe
    out your normal flora, leading to thrush and even
    candidemia. Imipenem is metabolized by the
    kidneys (it is given with cilastain in an attempt
    to decrease hydrolysis) and is also excreted by
    the kidneys. It is the most neurotoxic of the
    ß-lactams and causes grand mal seizures if blood
    levels are too high or vomiting if it is
    administered too quickly. Blood levels of
    imipenem are not possible because imipenem is
    extremely labile in aqueous solution. Therefore,
    in renal dysfunction, use meropenem, which can be
    monitored. Finally, carbapenems are stable to all
    ß-lactamases except those found in
    Stenotrophomonas maltophila this was selected
    for in ICUs.

19
18) The fluoroquinolone antibiotics share all of
the following characteristics EXCEPTA) they
are absorbed adequately in the intestineB) their
absorption is reduced by the presence of heavy
metal cations such as Mg and CaC) they have
very low MICs for Salmonella and ShigellaD) they
are lipophilic enough to diffuse well into
mammalian cellsE) they are inactivated by
plasmids that occur only in S. aureus
  • The answer is E
  • Fluoroquinolones are indeed given orally Mg, Ca,
    Fe, and antacids decrease absorption. They are
    active against Enterobacteriaceae. Apparently,
    they are lipophilic enough to diffuse well into
    mammalian cells. Plasmid-mediated resistance is
    uncommon instead, resistance is chromosomally
    mediated and relies on mutations in DNA gyrase
    (qnr gene in the case of Gram-negatives,
    mutations in the porins can also confer
    resistance). Also, aminoglycoside-modifying
    enzymes can modify the fluoroquinolones.

20
19) Which of the following antibiotics can be
given safely to a patient who has had a recent
anaphylactic reaction to penicillin G?A)
ampicillinB) aztreonamC) cefazolinD)
oxacillinE) none of the above
  • The answer is B
  • Owing to a different ring structure, there is no
    cross-allergenicity between aztreonam and the
    other ß-lactams.

21
20) Carithromycin differs from erythromycin in
which of the following?A) it is absorbed from
the gastrointestinal tract after oral
administrationB) it inhibits protein synthesis
by binding to the 50S ribosomal subunit of
susceptible bacteriaC) it inhibits E.coli at
concentrations that are easily achievable in
vivoD) it achieves substantially higher
intracellular concentrationsE) it is one of the
drugs of choice for treating Legionella
pneumoniae infections
  • The answer is D
  • Both erythromycin and clarithromycin inhibit
    bacterial protein synthesis by binding to the 50s
    ribosomal subunit and interacting with the 23s
    rRNA. Erythromycin can be used in infections by
    Gram-positives (including GAS), Legionella, and
    Mycoplasma in syphilis in diphtheria and in
    pertussis. Of the Gram-negative rods,
    erythromycin is active only against H. pylori, B.
    pertussis, and C. jejuni other Gram-negative
    rods outer membranes prevent entry of
    erythromycin. Clarithromycins spectrum of action
    is similar to erythromycins, except that
    clarithromycin has activity against some
    Gram-negative respiratory pathogens such as
    Haemophilus. Furthermore, clarithromycin can be
    used to treat H. pylori and atypical
    Mycobacterium infections. Both are given orally.
    I didnt know that clarithromycin had
    substantially higher intracellular concentrations
    than erythromycin.

22
21) All of the following are important
considerations in the choice of drug therapy for
malaria EXCEPTA) the presence of severe
gastrointestinal symptoms such as vomiting which
makes oral therapy difficultB) P. faciparum
infection, which is likely to be resistant to
chloroquineC) a history of penicillin allergy
because several antimalarial drugs are closely
related to penicillinD) the requirement for
additional therapy to treat the hepatic phase of
P.vivaxE) hemolytic reactions to primaquine,
which may occur if the patient has a
glucose-6-phosphate dehydrogenase deficiency
  • The answer is C
  • Treatment of vivax and ovale requires a tissue
    schizonticide such as primaquine to kill the
    liver hypnozoites.

23
22) All of the following are true of the
mechanisms of action of anti-malarial drugs
EXCEPTA) inhibitors of hemoglobin synthesis
look to be promising drugsB) chloroquine
inhibits the heme polymerase enzyme in the food
vacuole, allowing accumulation of toxic
hemoglobin breakdown productsC) artemisin (sweet
wormwood) has been used in China for centuries
and generates toxic free radicals when activated
by ironD) some drugs (pyrimethamine and
proguanil) act by inhibiting dihydrofolate
reductase and folic acid productionE) resistance
to chloroquine probably occurs by decreased drug
accumulation in the food vacuole
  • The answer is A
  • Chloroquine inhibits heme polymerization,
    resulting in accumulation of heme, a toxin to
    Plasmodium. Artemisin is not licensed in the US,
    but produces free radicals that kill the
    parasites. Pyrimethamine is a dihydrofolate
    reductase inhibitor (resistance is widespread)
    proguanil (often given with atovaquone for
    prophylaxis) also interferes with folate
    metabolism. Chloroquine resistance is probably
    due to reduced uptake or increased excretion of
    the drug. New approaches to treatment of malaria
    include inhibition of fatty acid synthesis (such
    as triclosan, which is in Softsoap and is
    currently used only as a topical antibacterial
    agent) inhibition of cysteine proteinases, which
    break down heme to peptides in the Plasmodium
    food vacuole inhibition of pyrimidine synthesis
    and L-adenosine analogues, which are taken up by
    infected RBCs.

24
23) All of the following are true of
aminoglycoside antibiotics that are used for
systemic infections EXCEPTA) they are excreted
primarily by glomerular filtrationB) they cause
cholestatic hepatitisC) daily dose must be
reduced in patients with moderate to severe renal
failure (GFR lt70ml/min/M2)D) streptococci are
inherently resistantE) they inhibit protein
synthesis
  • The answer is B
  • Erythromycin, a macrolide, causes cholestatic
    hepatitis. Aminoglycosides are excreted by
    glomerular filtration, dose must be reduced in
    patients with GFR lt 70, anaerobes and
    streptococci are intrinsically resistant because
    active transport of aminoglycosides depends on an
    electron transport chain, and aminoglycosides
    bind to the 30s ribosomal subunit, inhibiting
    protein synthesis.

25
24) Treatment of fungal infections is
particularly difficult for all of the following
reasons EXCEPTA) macromolecular synthesis in
fungi is similar to that of mammalian cells,
limiting potential targetsB) many of the
potential drugs are very toxicC) diffusion to
the site of infection is frequently limitedD)
lipids in fungal membranes are identical to those
in human cellsE) resistance frequently develops
  • The answer is D
  • Ergosterol in fungi, cholesterol in humans

26
25) A 50 year old paraplegic man is admitted to
the hospital with fever, flank pain, frequency,
and urgency. His white blood cell count is
15,000 with 85 polys, 6 bands. His urine has a
specific gravity of 1.010, pH 8, 50-100 WBC, and
20-30 RBC per high power field, and numerous
crystals. The most likely bacteria to be
cultured from his urine isA) E.coliB)
Enterococcus faecalisC) Klebsiella pneumoniaeD)
Proteus mirabilisE) Staphylococcus saphrophyticus
  • The answer is D
  • Proteuss urease converts urea into ammonia,
    hence alkalinizing urine.

27
26) All of the following are true of Amphotericin
B EXCEPTA) it has a complex chemical structure
which makes it insoluble in water at physiologic
pHB) it can only be administered intravenously
when treating systemic infectionsC) it has the
widest spectrum of activity against yeasts and
molds of any agentD) it preferentially binds to
ergosterol in fungal membranes, causing leakage
of cell contents and cell deathE) resistance
frequently develops by enzymatic degradation of
the drug
  • The answer is E
  • Resistance against amphotericin B does not
    develop, even if it is used alone. Cf. question
    75 for more facts.

28
27) A 70 year old patient from Thailand is
hospitalized in the CCU following a myocardial
infarction. A one meter long worm is detected
in his nasogastric tube. The most likely
explanation isA) he frequently ate sushi and
has anasakiasisB) he has ascaris infection and
the helminth is migrating from his
gastrointestinal tractC) he has hepatic
involvement with schistosomiasisD) he has
serious hookworm infectionE) he has disseminated
strongyloidiasis
  • The answer is B
  • According to Dr. Reed, Ascaris is the only worm
    you can diagnose over the phone because it is so
    big and long. Gross

29
28) All of the following are true about infection
with Stronglyoides EXCEPTA) asymptomatic
gastrointestinal infection can occurB) it is the
only helminth that can replicate within the human
hostC) its life cycle requires development
within specific species of carpD) disseminated
infection in an immunocompromised host can be
fatalE) patients may have low-grade symptoms of
skin rashes, abdominal discomfort and
intermittent diarrhea for decades
  • The answer is C
  • Strongyloides can cause asymptomatic infection or
    symptomatic infection of the GI and respiratory
    tracts. It is the only helminth that can
    replicate within the human host. Clonorchis, not
    Strongyloides, requires development within a
    specific species of carp. Strongyloides
    hyperinfection can be fatal and, according to Dr.
    Guatelli, is not uncommon. Finally, low-grade
    infection can indeed persist for decades.

30
29) All of the following infections are
transmitted by arthropods EXCEPTA) Borrelia
burgdorferiB) Yersinia pestisC) Rickettsia
rickettsiiD) Leptospira interrogansE)
Rickettsia typhi
  • The answer is D
  • Borrelia burgdorferi (the agent of Lyme disease)
    is transmitted by Ixodes ticks. Yersinia pestis
    (the agent of plague) is transmitted by rodent
    fleas. Rickettsia rickettsii (the agent of Rocky
    Mountain spotted fever) is transmitted by
    Dermatocentor ticks. Leptospira interrogans (the
    agent of leptospirosis) is transmitted in the
    urine of infected mammals. Rickettsia typhi (the
    agent of endemic typhus) is transmitted by rat
    and cat fleas.

31
30) A 17 year old male returns from a trip down
the Nile River. He has fever, malaise, and a
peripheral eosinophilia of 40. He admits to
swimming in the river, drinking nonbottled water,
and eating raw fruits and vegetables. The most
useful diagnostic test would beA) peripheral
blood smear for malariaB) schistosome serology,
and stool and urine examination to look for
schistosome eggsC) a string test for giardiaD)
a wet mount of stool to look for E.histolytica
trophozoitesE) an acid-fast smear of stool to
look for cryptosporidium
  • The answer is B
  • Eosinophilia is associated with infections by
    helminths rather than just by any old parasites.
    Dr. Reed really likes stressing that fact.

32
31) All of the following statements about the
three major mechanisms by which retroviruses may
lead to oncogenic transformation are true
EXCEPTA) retroviruses may insert into the host
cell genome and influence the transcription of
downstream cellular genes involved in cellular
growth and differentiation.B) retroviruses may
insert into the host cell genome and influence
the transcription of upstream cellular genes
involved in cellular growth and
differentiationC) retroviruses acquire cellular
genes called proto-oncogenes that are involved in
cellular growth and differentiation and transfer
these genes or modified versions of them to new
hostsD) a retroviral protein may act in trans to
influence the activity of other cellular genes
involved in cellular growth and
differentiationE) retroviruses that act by
insertional mutagenesis tend to be rapidly
transforming in vivo and in tissue culture
  • The answer is E
  • uhh

33
32) All of the following statements about the
regulation of HIV-1 transcription are true
EXCEPTA) tat protein acts in a
positive-feedback loop to up-regulate viral
transcriptionB) tat protein binds to the TAR
element of nascent viral transcripts to
facilitate transcriptional initiation or
elongation by RNA polymerase II.C) rev protein
binds to the REV-response element (RRE) and
promotes viral mRNA stability and nuclear
exportD) rev protein binds to RRE and induces
the transition from early production of unspliced
mRNAs to more fully processed, multiply spliced
mRNAsE) rev protein is a negative regulator of
its own production
  • The answer is D
  • tat binds TAR and facilitates transcription by
    RNA pol II. rev binds the rev response element
    (RRE) and promotes viral mRNA export into the
    cytoplasm. Without it, multiply-spliced mRNAs
    accumulate in the nucleus and a variety of
    proteins cannot be synthesized.

34
33) Six days after sustaining several flea bites
in a rat-infested shed in Southwest Texas, a
college student developed fever, chills and rash
that spread from his abdomen to cover his
extremities. Seven days later, the public health
department detected antibody to one of the
rickettsial group antigens. The most likely
diagnosis isA) Q-feverB) epidemic typhusC)
endemic typhusD) scrub typhusE) trench fever
  • The answer is C
  • Rickettsiaceae frequently cause an
    undifferentiated fever syndrome, characterized by
    the triad of fever, headache, and rash. Endemic
    typhus (Rickettsia typhi) is found along the
    CA-Mexico and TX-Mexico border as well as in
    Hawaii and is transmitted by rat and cat fleas.
    Epidemic typhus (Rickettsia prowazeckii) is found
    in many parts of Europe in Africa (in short, any
    place where people dont change their clothes
    much) and is transmitted by the human body louse.
    Scrub typhus (Orientsia tsutsugamushi) is
    transmitted by chiggers (trombiculid mites) and
    is found in southeast Asia. Q fever (Coxiella
    burnetti) is a zoonotic disease associated with
    parturition and causes doughnut-hole granulomas
    in the liver. Trench fever (Bartonella quintana)
    is transmitted by the human body louse (like
    Rickettsia prowazeckii, the agent of epidemic
    typhus) and emerged in homeless alcoholics in
    Seattle.

35
34) Which of the following statements are true of
both Sin Nombre Virus (SNV) and Lassa Fever Virus
(LFV)A) both viruses use exclusively a simple,
negative-strand transcriptional strategy.B) the
large (L) RNA segment of both viruses encodes the
viral polymeraseC) both viruses were identified
initially by polymerase chain reaction (PCR)D)
both viruses are readily transmitted from person
to personE) both viruses assemble in the
nucleus, and are only released upon cell lysis
  • The answer is B
  • Arenaviruses have two ambisense, single-stranded
    RNA segments (bunyaviruses, except for
    Phleboviruses, have three negative-sense,
    single-stranded, circular RNA segments).
    Arenaviruses package host ribosomes, two helical
    nucleocapsids, and transcriptase. L codes the
    transcriptase in both families. I dont think
    they ever taught us how the viruses were first
    identified. While LFV is transmitted from person
    to person (direct contact with body fluids,
    needlestick, or inhalation of aerosolized virus),
    there is no person-to-person transmission for
    SNV. Replication of both arenaviruses and
    bunyaviruses take place in the cytoplasm
    bunyavirus budding is from the smooth ER into
    intracytoplasmic vesicles and arenavirus budding
    is from the plasma membrane.

36
35) The Sin Nombre Virus (SNV) differs from most
other Bunyaviridiae in all of the following
EXCEPTA) SNV virus buds from the cell plasma
membraneB) SNV lacks both NSs and NSm
(nonstructural) proteinsC) SNV lacks separate G1
and G2 envelope glycoproteinsD) SNV uses only a
simple negative-strand transcription strategyE)
no insect vector is involved in transmission of
SNV
  • The answer is C
  • bad explanation follows Sin Nombre virus has G1
    and G2 envelope glycoproteins, like other
    bunyaviruses (these mediate attachment). It is a
    member of genus Hantavirus, which is a unique
    genus in family Bunyaviridae because there is no
    insect vectortransmission is from rodents to
    humans. It is also the only bunyavirus that lacks
    nonstructural proteins. Genus Phlebovirus is the
    only genus in Bunyaviridae containing viruses
    that utilize ambisense replication. SNV does bud
    from the cell plasma membrane, as shown in Dr.
    Looneys fluorescent images slide, but this is
    confusing because bunyaviruses bud from the ER
    into intracytoplasmic vesicles, forming the
    virion inside the vesicle, and then bud out of
    the plasma membrane, releasing the virion. I
    thought all bunyaviruses did this, which would
    make answer choice a a valid answer.

37
36) All of the following are related to
Hantavirus Pulmonary Sydrome EXCEPTA) Sin
Nombre VirusB) Peromyscus maniculatus (deer
mouse)C) Sigmodon hispidus (cotton rat)D)
Mastomys natelensis (multimammalate mouse)E)
Black Creek Canal Virus
  • The answer is D
  • The deer mouse and the cotton rat are vectors for
    Sin Nombre virus, which causes hantavirus
    pulmonary syndrome. Mastomys natelensis, the
    multimammilate mouse, is a common pet in
    Scandinavia and is associated with Lassa fever
    virus. I cant remember hearing about the black
    creek canal virus, ever.

38
37) From what you know about pathogenesis,
immunity and protection from infection with SNV
and/or other hantaviruses, which of the following
would you predict to be associated with a poor
outcome after Sin Nombre Virus infection?A) a
renal transplant recipient who still responds to
hepatitis B and pneumococcal vaccinesB) a
patient receiving an infusion of convalescent
plasma from a recovering twinC) a patient with
hypogammaglobulinemia (common variable
immunodeficiency)D) a patient receiving
interferon therapy for Hepatitis CE) a patient
with iatrogenic neutropenia due to
anti-staphylococcal penicillin therapy
  • The answer is C
  • Interferon is effective in vitro and in vivo
    against bunyavirus infections neutralizing
    antibodies are also produced in response to
    infection. That would suggest that antibodies are
    important, and a patient with hypogammaglobulinemi
    a would hence have a poor prognosis.

39
38) An E.coli from a urinary tract infection may
possess all of the following virulence factors
EXCEPTA) hemolysinB) LPSC) motilityD)
piliE) urease
  • The answer is E
  • Relevant virulence factors that allow E. coli to
    cause UTIs include hemolysin, which damages
    bladder mucosa LPS, which inhibits peristalsis
    flagella, which permit motility pili, which
    allow colonization of both upper and lower
    urinary tracts K1 capsule, which is
    antiphagocytic and aerobactin, a siderophore.

40
39) Which ONE of the following statements about
retroviral genomes and reverse transcription is
CORRECTA) retroviral virions contain two
PLUS-stranded, genetically identical genomic RNA
segments.B) retroviral virions contain two
MINUS-stranded, genetically identical RNA genomic
segmentsC) retroviral virions contain two
genomic RNA segments arranged in a double helix
that unwinds with the initiation of strong-stop
DNA synthesis (i.e. just after the tRNA primer
binds)D) retroviral virions contain two genomic
segments that are each composed of plus-stranded
RNA and may be heterozygous at multiple loci.E)
the first strand transfer (jump) occurs by
transposition of the minus-strand strong-stop DNA
(i.e., the initial U5 R repeat segment of DNA)
to the polypurine tract.
  • The answer is D
  • In general, Retroviridae have diploid ssRNA
    genomes HIV, in particular, has two () ssRNA
    strands that can be non-identical. I get really
    confused when I think about HIV reverse
    transcription.

41
40) Which of the following is true concerning
immunological and pathological responses to
infection with Bunyaviridae and ArenaviridaeA)
antibodies to the nucleocapsid (N) and envelope
(G1) glycoproteins almost never develop after
exposure to Sin Nombre Virus (or other
bunyaviruses) and are of little value in
diagnosis.B) Sin Nombre Virus produces
pneumonitis via direct lytic infection of type 1
pneumocytesC) virus shedding after infection
with Lassa Fever Virus is quite limited, ceasing
after rapid control of viremia is achieved by
neutralizing antibody directed against the viral
N proteinD) infection with Lassa Fever Virus is
particularly devastating in the native
population, where it occurs at a young age when
the immune system is not well developed. In
contrast, relatively minor manifestations of
disease are seen in previously naïve European
adults (e.g. volunteer physicians).E) antibody
mediated enhancement of macrophage infection by
Lassa Fever Virus may help explain the lack of
animal protection by passive immunization with
convalescent LFV sera.
  • The answer is E
  • IgG/IgM antibodies to N and G2 are used for
    diagnosis of hantavirus pulmonary syndrome. SNV
    stays in the vascular endothelium and does not
    replicate in pneumocytes rather, it induces the
    production of proteinaceous fluid that leaks into
    alveolar spaces and hence causes edema. In Lassa
    fever, viremia is quite long, which may be why
    ribavirin actually works. Lassa fever virus is
    pretty deadly to fetuses and neonates. While it
    causes moderate morbidity and mortality in
    indigenous populations, it causes high morbidity
    and mortality in outside visitors. Immunization
    with killed virus is not protective against LFV
    convalescent serum with antibodies is similarly
    not helpful.

42
41) Pseudomonas aeruginosa can grow under
anaerobic conditions because itA) ferments
glucoseB) ferments lactoseC) lacks oxidaseD)
lacks catalaseE) reduces nitrate to nitrite
  • The answer is E
  • P. aeruginosa respires only, but it can survive
    anaerobically because it uses nitrate, not
    oxygen, as the terminal electron acceptor.

43
42) Which organism can be transformed with
virulence and antibiotic resistance genes under
natural conditions?A) E.coliB) Bacteroides
fragilisC) Staphylococcus aureusD)
Streptococcus pneumoniaeE) Salmonella typhimurium
  • The answer is D
  • Natural transformers include the pneumococcus,
    the gonococcus, H. influenzae, and H. pylori.
    (The meningococcus apparently undergoes natural
    transformation, too, at least according to one of
    our winter term exams. Here, have some new genes.
    Kristen)

44
43) Bacterial conjugationA) Only occurs
between members of the same genus or speciesB)
can transfer both plasmid and chromosomal
genesC) transfers double-stranded DNAD)
requires certain outer membrane proteins on the
recipientE) only occurs naturally among
Gram-negative bacteria
  • The answer is B
  • Conjugation can occur between genera, can
    transfer both plasmid and chromosomal genes,
    involves the transfer of single strands of DNA,
    does not require outer membrane proteins on the
    recipient, and occurs naturally in both
    Gram-negatives and Gram-positives.

45
44) Recognized mechanisms of acquired resistance
to penicillin involve all of the following
EXCEPTA) active transport out of the
bacteriaB) decreased intra-cellular
concentrations due to porin mutationsC)
constitutive expression of inducible chromosomal
beta-lactamaseD) mutations in the target enzyme
in the inner membraneE) plasmid encoded
beta-lactamase
  • The answer is A
  • Resistance to ß-lactams is conferred by changing
    the PBP (transduced mec locus in the case of
    MRSA transformation in S. pneumoniae) or by
    inactivation of the antibiotic with a
    ß-lactamase. It can also be conferred in
    Gram-negatives by mutations in porins that alter
    the ability of the antibiotic to reach the cell
    wall. Efflux pumps are seen in resistance to
    tetracyclines (plasmid-mediated) and
    fluoroquinolones.

46
45) Capsules are important in the pathogenesis of
infection withA) Actinomces israeliiB)
Bacteroides fragilisC) Clostridium difficileD)
Clostridium tetaniE) Corynebacterium diptheriae
  • The answer is B
  • B. fragilis has an antiphagocytic capsule that
    alone can produce an abscess.

47
46) Plasmid-mediated resistance to which
antibiotic involves the synthesis of an enzyme
that alters cell wall precursor structure?A)
cephalosporinsB) cycloserineC) INHD)
penicillinsE) vancomycin
  • The answer is E
  • Vancomycin-resistant enterococci have plasmids
    that code for enzymes that synthesize D-ala-D-lac
    instead of D-ala-D-ala in the N-acetylmuramic-acid
    -N-acetyl-glucosamine backbone of PDG.

48
47) Single-step mutations to high level
resistance occur with A) gentamicinB)
metronidazoleC) penicillinD) rifampinE)
vancomycin
  • The answer is D
  • Resistance to rifamycins occurs when RNA pol is
    altered. This resistance is chromosomally-mediated
    and occurs in one step. Resistance to
    aminoglycosides can be intrinsic (aminoglycosides
    rely on ETC to get in, so anaerobes and
    streptococci are resistant) streptomycin
    resistance occurs when a one-step chromosomal
    mutation changes the binding site on the S12
    protein on the 30s subunit (but with newer
    aminoglycosides, several such mutations are
    required) finally, aminoglycosides can also be
    inactivated by enzymes at various sites (but
    amikacin has only two sites that can be modified,
    making resistance harder to come by). Resistance
    to metronidazole is seen (rarely) in B. fragilis
    (via a plasmid) otherwise, Actinomyces is
    intrinsically resistant. Resistance to ß-lactams
    is conferred by changing the PBP (transduced mec
    locus in the case of MRSA transformation in S.
    pneumoniae) or by inactivation of the antibiotic
    with a ß-lactamase. Resistance to vancomycin is
    found in enterococci, where a plasmid codes for
    enzymes that synthesize D-ala-D-lac instead of
    D-ala-D-ala, the target of vancomycin.

49
48) Inhibits DNA gyrase activityA)
CiproflaxinB) clarithromycinC) metronidazoleD)
rifampinE) trimethoprim
  • The answer is A.
  • Period.

50
49) Which of the following statements is true of
Haemophilus influenze?A) polyribitol phosphate
(PRP) is critical for pathogenesisB) it causes
meningitis only in neonatesC) terminal
complement components are critical for natural
resistanceD) it is now the most common cause of
meningitis in children between 6 months and 6
years of age in the United StatesE) none of the
above
  • The answer is A
  • H. influenzae type B has a pathogenic capsule
    made of polyribitol phosphate. It causes
    meningitis in individuals under the age of five
    who have not been immunized. Natural resistance
    is conferred by antibodies against capsules
    produced by other bacteria (such as E. coli,
    capsule type K100) by the age of five, such
    antibodies are usually present, and therefore
    disease is not common over the age of five even
    in non-immunized individuals. In the US, the most
    common cause of meningitis in children older than
    two years of age and teenagers is N.
    meningitidis.

51
50) All of the following are true of cryptococcal
meningitis EXCEPTA) the most common
predisposing illness in the USA is AIDSB) it can
be diagnosed by the pesence of capsular antigen
in the CSFC) it is fatal if untreatedD) it can
occur in immunologically normal hostsE) it is
usually spread person to person
  • The answer is E
  • No fungi are usually spread from person to
    person. The vast cases of cryptococcal meningitis
    are seen in AIDS patients. It is a primary
    pathogenic fungus, which means it is dimorphic.
    Diagnosis of Crypto is based on antigen and
    culture for Cocci, antibody titer is sensitive
    and specific while culture is the gold standard.

52
51) In which of the following drug combinations
do both drugs have intrinsic antimicrobial
activity?A) clavulinic acid-amoxicillinB)
imipenem-cilistatinC) sulbactam-ampicillinD)
tazobactam-piperacillinE) trimethoprim-sulfametho
xisole
  • The answer is E
  • Period.

53
52) All of the following are true of the
replication of Lassa Fever Virus (LFV)
EXCEPTA) LFV is exquisitely sensitive to the
action of interferon, and is rapidly cleared
early in infection by host antibodyB) LFV
typically buds from the surface of infected
cells, accounting for the presence of viral
glycoprotein on the cell surface during active
replicationC) LFV enters cells by pH dependent
membrane fusion, and infection is sensitive to
lysosomatropic agentsD) LFV is sensitive to high
concentrations of a-amanitin, suggesting that
some host cell RNA transcription may be needed
for efficient parasitism of cellular capping
signalsE) Arenaviridae typically require at
least 36-60 hour for peak production of viral
proteins, in contrast to Bunyaviridae, which
replicate much more rapidly and are typically
more cytopathic in vitro
  • The answer is A
  • Interferon is not useful against Lassa Fever
    virus or any arenaviruses, for that matter.
    Arenaviruses, including LFV, do make glycoprotein
    and do bud from the plasma membrane. There is
    evidence for both pH-mediated fusion as well as
    direct membrane fusion. I dont think anyone
    taught us about amanitin. Bunyaviridae are
    certainly more cytopathic and faster-replicating
    than Arenaviridae.

54
53) The major therapeutic advantage of
piperacillin over ampicillin isA) it inhibits
penicillinase producing S. aureusB) it inhibits
Group A b-hemolytic streptococciC) it inhibits
enterococciD) it is not nephrotoxicE) it
inhibits Pseudomonas aeruginosa
  • The answer is E
  • Fourth-generation penicillins include mezlocillin
    and piperacillin (the ureidopenicillins) and
    carbenicillin and ticarcillin (the
    carboxypenicillins). They have activity against
    nasty Gram-negatives such as P. aeruginosa.
    Penicillins are pretty much nontoxic. Even the
    first-gen penicillins work against GAS. The
    ureidopenicillins (mezlocillin and piperacillin)
    do not work against penicillinase-producing S.
    aureus. Referring only to our syllabus, its not
    clear how the activities against enterococci
    differ between piperacillin and ampicillin, but
    piperacillin certainly has activity against
    enterococci.

55
54) Congenital infection has been described with
each of the following infection agents
EXCEPTA) Gardnerella vaginalisB) Rubella
virusC) Toxoplasma gondiiD) Treonema
pallidumE) Varicella Zoster Virus
  • The answer is A
  • Congenital infections are classically caused by
    STORCH (syphilis, Toxoplasma, rubella, CMV, and
    HSV). Varicella is a rare congenital infection
    (HSV is too, according to Dr. Spector) that
    causes scarring, short limbs, mental retardation,
    and other bad stuff.

56
55) Potential advantages of live attenuated
vaccines compared to inactivated or subunit
vaccines include all of the following EXCEPTA)
activates all phases of the immune systemB)
greater thermostabilityC) immunity is more
durable and effectiveD) lower cost of
productionE) provides local (mucosal) immunity
  • The answer is B
  • Pros of live attenuated vaccines include
    activation of all phases of the immune system,
    more durable and efficient immunity, lower cost
    of production, and induction of local (mucosal)
    immunity. They are more sensitive to
    environmental conditions than inactivated
    vaccines.

57
56) All of the following can cause chronic
persistent infections EXCEPTA) BK virus B)
Epstein Barr virusC) Hepatitis B virusD)
Hepatitis C virusE) Hepatitis E virus
  • The answer is E
  • Hep A and Hep E are the two hit-and-run hepatitis
    viruses.

58
57) All of the following are ture of viral
gastroenteritis EXCEPTA) enteroviruses cause
10-15 of the cases in adults and childrenB)
Norwalk virus and related viruses cause as many
as 40 of epidemics of acute viral gastoenteritis
in adults and older childrenC) group A rotavirus
is the most common cause of severe dehydrating
diarrhea in infantsD) the stool is
noninflammatory with no white cells or red cells
on microscopic examinationE) infection is
confined to the gastrointestinal tract and there
is no evidence of viremia
  • The answers are actually A E
  • As updated by Dr. Guatelli on the portal, Viremia
    is actually fairly common during gastroenteritis
    due to Rotavirus.
  • a and e are both valid answers, as confirmed by
    Guatelli, who even posted his reply online.
  • Rotavirus diarrhea is not usually bloody and does
    not usually contain WBCs, though in 10 to 20 it
    may.
  • Viremia occurs in 50 of children infected with
    Rotavirus, although this correlates neither with
    severity nor with extraintestinal manifestations.
  • On the other hand, Norovirus diarrhea has no WBCs
    or RBCs.
  • Enteroviruses largely cause polio and aseptic
    meningitis.

59
58) The structure responsible for the gram
positivity of streptococci isA) cytoplasmic
membraneB) hyaluronic acid capsuleC)
lipteichoic acidD) M proteinE) peptidoglycan
  • The answer is E
  • Peptidoglycan retains the Gram stain.

60
59) Animal reservoirs play an important role in
the ecology of all of the following EXCEPTA)
influenza A virusB) influenza B virusC) Lassa
fever virusD) lymphocytic choriomeningitis virus
(LCM)E) yellow fever virus
  • The answer is B
  • Influenza B and C are human viruses only.
    Influenza A has a waterfowl reservoir. Lassa
    fever virus and lymphocytic choriomeningitis
    virus, like all arenaviruses, are parasites of
    rodents. Yellow fever virus is a member of family
    Flaviviridae, and several members of Flaviviridae
    (West Nile, yellow fever, dengue, Japanese
    encephalitis B, St. Louis encephalitis) are
    arboviruses.

61
60) All of the following are true of rabies virus
EXCEPTA) It is a member of the Rhabdovirus
familyB) it has a virion polymeraseC) it is
inactivated by lipid solventsD) it attaches
selectivity to nicotinic acetylcholine receptors
E) it establishes latent infection in neurons in
the limbic system
  • The answer is E
  • Rabies virus, a member of Rhabdoviridae, has a
    (-) ssRNA genome, and as such has a virion
    polymerase (the L protein). One of its receptors
    is the nicotinic acetylcholine receptor.
    Apparently, it is inactivated by lipid solvents
    (where did we learn that?). The limbic system is
    indeed infected, but the infection does not
    become latentdeath follows soon after the onset
    of symptoms.

62
61) Human infection is necessary to maintain all
of the following pathogens in the nature
EXCEPTA) Group A b-hemolytic streptococcusB)
J.C. virusC) Junin virus (the cause of Argentine
hemorrhagic fever)D) Neisseria meningitidisE)
Varicella-Zoster virus
  • The answer is C
  • GAS is an exclusive human pathogen.
    Polyomaviridae are very host-specific, and
    therefore JC produces abortive infections in
    non-human species, relying instead on humans for
    propagation of infective virions. Junin virus is
    a member of family Arenaviridae, and each
    arenavirus has a rodent host in which it produces
    persistent infection. Pathogenic Neisseria spp.
    are obligate human pathogens. VZV, like HSV-1 and
    HSV-2, is an alpha herpesvirus alpha
    herpesviruses have a wide host range, but
    apparently human infection is necessary to
    maintain the pathogens in nature.

63
62) Protease inhibitors inhibit HIV replication
by interfering withA) integration of proviral
DNA into the host cell genomeB) reverse
transcriptaseC) transactivation by tatD) virus
attachment to CD4E) virus maturation
  • The answer is E
  • The HIV protease processes the Gag and Gag-Pol
    proteins this processing is necessary for
    formation of the viral core as well as for
    activation of the integrase and reverse
    transcriptase. If the protease is inhibited,
    virions produced are uninfectious.

64
63) All of the following are true of the current
human rabies vaccine EXCEPTA) it is produced
in diploid human fibroblastsB) it is a live
attenuated vaccineC) it does not induce allergic
encephalomyelitis as did some earlier rabies
vaccinesD) it should be administered at the same
time as human rabies immune globulin to
susceptible persons as soon as possible after
potential exposure to rabiesE) it should be
administered prophylactically to persons (i.e.,
veterinarians) who may be at risk of exposure to
rabies
  • The answer is B
  • The human diploid cell rabies vaccine (HDCV) is
    the only one of the three vaccines available that
    has an approved formulation for preexposure
    vaccination. Absorbed rabies vaccine (RVA) and
    purified chick embryo cell vacine (PCECV) are the
    other two vaccines. All are killed and all are
    administered intramuscularly, commonly in the
    deltoid in adults and in the thigh in children.
    With previous vaccines derived from duck embryos,
    allergic encephalomyelitis occurred in 1. Even
    prior to that, vaccines derived from brain tissue
    elicited this in 10-20 of those vaccinated. In
    addition to washing bite wounds and scratches
    with soap and water, antirabies immunoglobulin
    preparations should be administered
    simultaneously (though presumably in the opposite
    arm than the vaccine).

65
64) The primary advantage of prodrugs like
famciclovir and valaciclovir isA) broader
spectrum of activity (e.g. including
adenoviruses, cytomegalovirus, papillomaviruses)
than the drugs from which they are derived
(penciclovir and acyclovir, respectively)B) less
hematologic and CNS toxicity than the drugs from
which they are derivedC) greater CNS penetration
than the drugs from which they are derivedD)
greater biovailability following oral
administration that the drugs from which they are
derivedE) all of the above
  • The answer is D
  • Famciclovir and valacyclovir are prodrugs of
    penciclovir and acyclovir, respectively, which
    are nucleoside analogs. They have higher
    bioavailability than their active metabolites.
    They are no more effective than acyclovir against
    suppression of chronic HSV. The half-life of
    penciclovir is greater than that of acyclovir.
    Side effects, spectrum of activity, and CNS
    penetration of famciclovir and valacyclovir are
    the same as those of acyclovir.

66
65) The cephamycins have the best activity
against B. fragilis of all the cephalosporins
becauseA) they are more resistant to the
chromosomal cephalosporinase (beta-lactamase)B)
they have a longer half-lifeC) they interfere
with vitamin K synthesis required by the
organismD) they are secreted into the gut and so
achieve higher intra-luminal concentrationsE)
they are prodrugs that are converted by anaerobic
bacteria to the active drug
  • The answer is A
  • I dont remember learning about cephamycins, but
    they include cefotetam and cefoxitin (which are
    both grouped in the second-generation
    cephalosporins). They have better activity
    against anaerobes, apparently because they are
    more resistant to the chromosomal
    cephalosporinase.

67
66) Viremia is not required for this virus to
cause CNS diseaseA) cytomegalovirusB) Eastern
equine encephalitis virusC) echovirus 9D)
HIV-1E) rabies virus
  • The answer is E
  • Rabies either enters peripheral nerves
    immediately after a bite (if the dose is large)
    or else multiplies in skeletal muscle cells near
    the site of inoculation prior to entry into
    unmyelinated sensory and motor nerves. The virus
    reaches the CNS via retrograde axonal spread, and
    as a result, the incubation interval depends on
    the proximity of the bite to the CNS. Once it
    gets to the CNS, anterograde (centrifugal) spread
    through other peripheral nerves ensues. Viremia
    is not required.

68
67) Rabies immune globulin and rabies vaccine are
indicated for each of the following EXCEPTA) a
bat enters a bedroom at night and bites a
sleeping child. The bat escapes.B) an American
tourist is bitten by a stray dog in Mexico. The
dog escapes.C) A child is bitten while feeding a
squirrel in Balboa Park. The squirrel escapes.D)
a woman is bitten by a raccoon while emptying her
trash in suburban Maryland. The raccoon
escapes.E) a man is bitten by a skunk while
washing his car in suburban Atlanta. The skunk
escapes.
  • The answer is C
  • Rabies is endemic in skunks and bats in CA
    raccoons in New England foxes in Europe
    mongooses in India and dogs, rats, and mongooses
    in Asia. If bitten by a rodent or a rabbit in the
    US, do not treat or consult because rabies is not
    endemic in these animals.

69
68) E. coli that causes gastrointestinal
infection can be differentiated from
nonpathogenic E.coli byA) distinctive
appearance on gram stainB) inability to ferment
lactoseC) identification of their pathogenic
genes or gene productsD) synthesis of
antiphagocytic capsulesE) synthesis of
supranormal amounts of LPS
  • The answer is C
  • All E. coli ferment lactose and look the same on
    Gram stain. EPEC is detected by antibodies
    against O antigens. Diagnosis of ETEC is not
    practical because of the large number of O types.
    EHEC has phage-encoded Shiga-like toxin (SLT-1)
    subtype O157H7 is unique because it is
    sorbitol-fermentation-negative.

70
69) All of the following are true of chronic
granulomatous disease (CGD) EXCEPTA)
polymorphonuclear leukocytes (PMN) fail to
oxidize nitro blue tetrazolium saltsB) the
X-lined form is usually associated with a detect
in the gene encoding the 91kd subunit of
cytochrome b588C) the autosomal form is usually
associated with a defect in the gene encoding the
47kd or the 67kd cytosolic component of the NADPH
oxidase systemD) patients with CGD have
recurrent Group A b-hemolytic streptococcal
infectionE) patients with CGD have recurrent
infections with catalase-positive organisms,
especially Staphylococcus aureus and Serratia
marcescens
  • The answer is D
  • CGD is a heterogeneous group of inherited
    disorders of phagocytes. The most common form is
    an X-linked defect in part of cytochrome b558.
    Prophylaxis against infections is with IFN-?
    and/or antibiotics (particularly
    trimethoprim/sulfamethoxazole). S. aureus and
    Serratia marcescens are particularly common.
    Letendre described the latter in a 2yo boy with
    cervical lymphadenopathy caused by a member of
    family Enterobacteriaceaethis turned out to be
    S. marcescens. CGD patients are susceptible to
    pyogenic infections caused by catalase-positive
    organisms, and therefore GAS isnt a
    characteristic infection in CGD patients.
    (Streptococci lack heme-containing enzymes, such
    as catalase, but they do have superoxide
    dismutase and peroxidase.) The syllabus mentions
    S. aureus, B. cepacia, S. marcescens, Nocardia
    spp., and Aspergillus spp. as the most common
    causes of infections in CGD patients.

71
MatchingA) CatalaseB) FlagellaC) Quellung
reactionD) UreaseE) Hemolysis___70.
Correlates with resistance to phagocytosis___71.
Correlates with the ability of Listeria
monocytogenes to lyse phagosomes and escape into
the cytoplasm___72. Correlates with the capacity
to spread from the bladder to the kidney___73.
Correlates with nephrolithiasis___74.
Correlates with survival and replication in
polymorphonuclear leukocytes of patients with
chronic granulomatous disease
  • The answers are
  • 70. C The Quellung reaction detects/types
    capsules, and capsules are important for
    resistance to phagocytosis.
  • 71. E Perhaps Listerias listerialysin O, which
    confers its ability to lyse phagosomes and escape
    into the cytoplasm, also acts as a hemolysin.
  • 72. B Flagella in E. coli allow for motility
    and retrograde spread of lower UTIs.
  • 73. D as with Proteus spp.
  • 74. A cf. question 69

72
MatchingA) Amphotericin BB) 5-FlucystosineC)
FluconazoleD) Trimethoprim-Sulfamethoxazole
(Septra or Bactrim)E) Erythromycin___75.
Always causes a dose-related renal
toxicity___76. Remains the most effective
therapy for Pneumocystis carinii infection but
drug reactions are a problem___77. Works
synergistically with Amphotericin B and is very
effective in the treatment of crytpococcal
infection___78. Inhibits a major enzyme in
ergosterol synthesis
  • The answers are
  • 75. A Amphotericin B binds to ergosterol in the
    fungal membrane, increasing membrane
    permeability. Its toxicity is related to its
    binding of cholesterol. Immediate toxicity is
    fever and chills in 50 (shake and bake) renal
    toxicity is dose-dependent and manifests as renal
    tubular acidosis with loss of potassium,
    phosphate, and magnesium. Newer methods of
    delivery include entrapment in liposomes, but
    this is very expensive.
  • 76. D Trimethoprim/sulfamethoxazole is used for
    prophylaxis against and treatment of Pneumocystis
    pneumonia. Drug reactions include allergic rash
    and megaloblastic anemia, reversible hepatitis in
    AIDS patients, kernicterus in infants, and
    hyperkalemia.
  • 77. B 5-flucytosine interferes with DNA
    synthesis. If it is given alone, resistance
    develops rapidly. If amphotericin B is given
    alone, resistance does not develop. Together,
    they are used to treat systemic fungal infections
    such as those caused by Cryptococcus or Candida.
  • 78. C The azoles deplete fungi of ergosterol

73
MatchingA) sulbactam-ampicillinB)
trimethroprim-sulfamethoxizoleC)
imipenem-cilistatin___79. Inhibits a human
enzyme that hydrolyzes the active drug___80.
Inhibits bacterial enzymes that hydrolyze the
drug___81. Inhibits the next enzyme in a
sequence that ordinarily synthesizes a required
cofactor
  • The answers are
  • 79. C Cilastatin inhibits renal tubular
    hydrolysis of imipenem.
  • 80. A Sulbactam, clavulanic acid, and
    tazobactam are ß-lactamase inhibitors.
  • 81. B Sulfonamides inhibit folate synthesis and
    trimethoprim inhibits dihydrofolate reductase.

74
MatchingA) Trichomonas vaginalis vaginitisB)
Candida albicans vaginitisC) Nonspecific
bacterial (anaerobic) vaginitisD) Chlamydial
cervicitisE) Gonococcal cervicitis___82.
Recurrent severe infections are an indication to
test for underlying HIV infection___83. Can be
diagnosed by finding small extracellular
organisms in secretions by fluorescent monoclonal
antibody staining
  • The answers are
  • 82. B Recurrent candidal vulvovaginitis may be
    a sign of HIV infection. Pseudohyphae or budding
    yeasts can be seen in candidiasis. Treatment is
    with oral or topical imidazoles (fluconazole or
    miconazole/clotrimazole, respectively).
  • 83. D Diagnosis of chlamydial infection is made
    via antigen detection (DFA, ELISA), genetic
    probes, or nucleic acid amplification tests
    (NAAT culture is not usually performed
    clinically). C. trachomatis infection is the most
    common reportable disease in the United States.
    It is asymptoma
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