Microbiology Review

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Microbiology Review

• Ericka King, tutor
• efking_at_u.washington.edu

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Some definitions

• Colonization establishment of a microbial
  population in a host
• Normal flora bugs that live in healthy people
• Resident there all the time, pretty much
• Transient briefly inhabit after an exposure
• Infection colonization by a pathogen
• Person may get sick or be a
• Carrier colonized but free of disease may
  spread

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Primary Pathogens

• Capable of producing disease in a healthy host -
  virulent organisms
• How identify these? Kochs postulates
• Regularly found in lesions of disease
• Isolated in pure culture (iffy in the real world)
• Take from culture, give it to another animal -gt
  can re-isolate from new lesions produced

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Opportunistic pathogens

• Microbe that can produce disease in hosts with
  compromised immune systems

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Normal Flora

• Prevent colonization by pathogens
• Competition for housing, resources
• Production of bacteriocins
• Antibiotic-like substances keep pathogens in
  check
• Source of potential pathogens
• Immunosuppression
• Reservoir for antibiotic resistance genes

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Colonic flora - protectors of the meek
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Places that should be sterile

• Blood
• CSF
• Synovial fluid
• Pleural, peritoneal cavities
• Deep tissues
• Most of GU tract

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Places that are decidedly not sterile

• Skin
• Oral cavity
• Nasopharynx
• Colon
• vagina

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What do I need to know about the bugs that
comprise the normal flora?

• Right now, not much
• Just keep this all in mind for when we talk about
  each one of these bugs
• Most are anaerobes
• The colon is replete with friendly flora

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Flora of the vagina

• Lactobacilli
• Produce peroxide -gt kills off other bacteria
• Predominant in healthy females
• Gardnerella vaginalis
• Group B strep
• Colonize during pregnancy
• Stuff from colon
• Anaerobes
• E. coli -gt big agent in UTIs

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Bacterial vaginosis

• Loss of Lactobacillus species -gt abnormal flora
• Overgrowth of
• Gardnerella vaginalis
• Gram variable
• Coccobacilli
• Anaerobes (G-)
• Prevotella
• Porphyromonas
• Bacteroides
• Production of amines -gt exfoliation of epithelial
  cells, transudation

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Bacterial Vaginosis

• Prevalence common, especially in WSW
• Risks sexual activity
• Sx abnormal vaginal odor, discharge
• Dx clue cells on vaginal smear, pH gt4.5, fishy
  smell on addition of KOH - whiff test
• Rx antibiotics, oral and topical (probiotic?)
• Complications infection farther up -
  salpingitis, PID, endometritis, premature labor

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Question 1

• The normal bacterial flora of the colon is
  comprised primarily of
• E. coli
• Gram positive organisms
• Strict anaerobes
• Lactobacilli
• Strict aerobes

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Question 1

• The normal bacterial flora of the colon is
  comprised primarily of
• E. coli
• Gram positive organisms
• Strict anaerobes
• Lactobacilli
• Strict aerobes

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Question 2

• Which of the following sites would be colonized
  by the fewest bacteria in a healthy person?
• Stomach
• Colon
• Nasopharynx
• Skin
• vagina

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Question 2

• Which of the following sites would be colonized
  by the fewest bacteria in a healthy person?
• Stomach
• Colon
• Nasopharynx
• Skin
• Vagina

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Question 3

• Diagnosis of bacterial vaginosis involves
• Culture and ID of causative pathogen
• Demonstration of antibodies in patients serum
• Direct detection of pathogen in vaginal
  secretions, using specific antibody
• Gram stain and determination of vaginal pH,
  presence of amines

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Question 3

• Diagnosis of bacterial vaginosis involves
• Culture and ID of causative pathogen
• Demonstration of antibodies in patients serum
• Direct detection of pathogen in vaginal
  secretions, using specific antibody
• Gram stain and determination of vaginal pH,
  presence of amines

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Host defenses

• Skin - one heck of a barrier
• Mucosa - needs some help
• Normal flora
• pH
• Movement
• Cilia
• Peristalsis
• Fluid flow
• Secreted stuff - IgA, lysozyme

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Host defenses, contd

• Deeper tissues - need active hunters
• Phagocytic cells
• PMNs, macrophages
• Eat bugs that have been opsonized
• Antibodies
• Cytotoxic T cells
• Know what types of defenses employed by each
  organ system

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How bacteria sneak by our defenses

• Tricking the phagocytes
• Capsule, slime layer - cant catch me
• Destruction of phagocytes - the trojan horse
• Mess up cell signalling
• Hanging out inside phagocytes
• Escape from alcatraz (phagosome)
• Stay in phagosome, but prevent lysosomal fusion
• Let endosomes fuse, but resist lysosomal enzymes

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Mechanisms of celluar damage

• Bacteria can hurt us directly
• We can hurt ourselves in trying to hurt them

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Bacterial Toxins

• Exotoxins G and G-
• Cause many diseases - botulism, tetanus, cholera
• Can be
• Pyrogenic - induce cytokine r elease -gt fever,
  toxic shock
• Tissue invasive -gt let bug tunnel through tissues

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More bacterial toxins

• Enterotoxins
• Act on GI tract - diarrhea, food poisoning
• Endotoxins (G- only)
• Lipid A portion of LPS, from outer membrane
• Released when bacterial cell lyses - not excreted
• Very toxic

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Immune-mediated damage

• Ab-Ag complex deposition
• Ex. Glomerulonephritis
• Autoimmune reactions
• Ex. Rheumatic fever

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A word about vaccines

• Live attenuated
• limited in ability to cause disease - less
  virulent mutant, from other species
• Especially useful for bugs that require CD8
  responses (ex. Enveloped viruses)
• Killed
• Subunit - specific epitopes that elicit Ab
  response
• Toxoid - against a toxin the bug makes

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Question 4

• Ciliated epithelium is an important antibacterial
  defense of the
• Gastrointestinal tract
• Genital tract
• Conjunctiva
• Urinary tract

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Question 4

• Ciliated epithelium is an important antibacterial
  defense of the
• Gastrointestinal tract
• Genital tract
• Conjunctiva
• Urinary tract

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Question 5

• Cephalosporins belong to which class of
  antibiotics?
• ß-lactams
• Tetracyclines
• Cyclosporins
• Anti-folates
• Glycopeptides

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Question 5

• Cephalosporins belong to which class of
  antibiotics?
• ß-lactams
• Tetracyclines
• Cyclosporins
• Anti-folates
• Glycopeptides

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Are you ready for the bugs?
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Gram Positive Bugs

• Cocci Rods
• Clusters chains worry about it
• later
• Staph ? hemol ? hemol
• Group A S. pneumo
• Group B viridans

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Streptococci

• G cocci in a chain
• aerotolerant anaerobes
• Catalase negative (vs. Staph)
• Differentiate via hemolytic pattern

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Strep pyogenes (group A)
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Strep pyogenes (group A)

• ? hemolytic - lyse RBCs
• Virulence factors
• Antiphagocytic capsule (hyaluronic acid)
• Cell surface
• M protein - inhibits complement activation,
  adhesion Abs directed against this
• Lipoteichoic acid (cells wall) - attachment

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Strep pyogenes toxins

• Streptolysin O (Oxygen labile)
• Pore forming destroys RBCs, WBCs -gt reason for ?
  hemolysis
• Antigenic
• Streptolysin S (Oxygen Stable)
• Destroys RBCs, WBCs
• Not antigenic
• Pyrogenic exotoxin
• Not in all strains
• When these strains invade, cause toxic shock,
  rash, fever
• superantigen

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Strep pyogenes

• Enzymes
• Hyaluronidase
• Cleaves hyaluronic acid
• Spreading factor
• Streptokinases
• Lysis of blood clots

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Strep pyogenes diseases

• Pharyngitis - sore throat, fever
• Scarlet fever - strains w/pyrogenic exotoxin
  diffuse rash on trunk/neck, strawberry tongue
• Toxic shock syndrome - also mediated by pyrogenic
  exotoxin release

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Strep pyogenes diseases

• Skin infections
• Impetigo (most common in kids, around mouth)
• Cellulitis (skin subQ infection)
• Erysipelas (elderly)
• Necrotizing fasciitis
• Enter through break in skin, spread along fascia
  deep to subQ
• Skin dies, muscle may become infected
• High mortality rate, even with Rx (50)

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Impetigo
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Strep pyogenesstill more

• Diseases caused by immune reaction
• Rheumatic fever
• Only after pharyngitis, not skin infection
• Molecular mimicry - reaction of Abs to heart
• Initial myocarditis, joint swelling, chorea, rash
• Years later, get valve disease mitralgtaortic
• Glomerulonephritis
• After pharyngitis or skin infection
• Deposition of immune complexes damages kidney

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Keep on truckin with S. pyogenes

• Acquisition
• from normal flora (20 kids, 10 adults
  colonized)
• Droplet transmission
• Dx
• culture - bacitracin-sensitive
• serology

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Strep agalactiae (group B)

• 3 Bs
• ? hemolytic
• Bacitracin resistant (vs. pyogenes)
• Baby diseases

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Strep agalactiae

• Polysaccharide capsule required for virulence
• Colonize vagina in 25 of pregnant women can
  transmit to baby at time of birth
• Neonatal diseases
• Early onset (lt7 days)
• Neonatal pneumonia
• 20-30 have meningitis
• Late onset (7 days - 3 months)
• Neonatal meningitis in 90

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Strep agalactiae

• Adult diseases especially in immunocompromised
• Osteomyelitis
• Bacteremia
• UTIs in pregnant women

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Strep pneumoniae

• ? hemolytic
• Pairs/short chains
• Optochin sensitive (vs. viridans)
• Infants 6 mo - 2 years, elderly most susceptible

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Strep pneumo

• Anti-phagocytic capsule (bunches of serotypes)
• Antigenic
• Enzymes
• Pneumolysin epithelial cell cytotoxin
• Inhibits cilia

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Strep pneumo

• Diseases
• Pneumonia - generally lobar
• Meningitis
• Sinusitis
• Otitis media - most common cause in kids
• Acquisition
• Rare person-person spread
• Inhabits throat, nasopharynx
• Dx sputum gram stain/culture

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Enterococci

• ? hemolytic (usually)
• Bacitracin resistant, optochin resistant
• Intrinsic acquired antibiotic resistance
• Scary nosocomial pathogen (vancomycin)
• Normal flora of colon
• Secrete bacteriocins
• Adhesive factors

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Enterococci

• Diseases
• UTIs, especially with catheters
• Abdominal abscess
• Wounds
• Endocarditis
• Bacteremia
• Dx blood agar

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Viridans strep

• ?- and non-hemolytic
• No capsule or toxins -gt low virulence
• Colonize oropharynx, GI
• Subacute bacterial endocarditis

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Gram Positive Bugs

• Cocci Rods
• Clusters chains worry about it
• later
• Staph ? hemol ? hemol
• Group A S. pneumo
• Group B viridans

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Staphylococci

• Gram cocci in clusters
• (If I had a copy of I heard it through the
  grapevine, I would play it for you)
• Catalase (vs. Step)
• Facultative

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Staph aureus

• ? hemolytic
• Coagulase (vs. other Staph)
• Hangs out in nares (especially health care
  workers)

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Staph aureus virulence (selected factors)

• Protein A - binds Fc portion of IgG, protects
  from opsonization, phagocytosis
• Coagulase - forms blood clot shield
• ? toxin- pore forming lyses blood cells
• Beta lactamase in many strains (70-80)
• Bunches of lipases, proteases that enable spread
  through tissue
• Exfoliatin causes skin to slough of
• Enterotoxins
• TSST-1 - not in all strains superantigen

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Staph aureus toxin-mediated diseases

• Food poisoning
• Ingestion of pre-formed enterotoxin
• Nausea, vomiting, diarrhea 12-24 hours
• Toxic shock syndrome
• Exotoxin TSST-1 stimulates cytokine release
• Fever, hypotension, rash
• Scalded skin syndrome
• Strain with exfoliatin toxin
• Neonates - causes skin to cleave mid-epidermis
  peel

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S. Aureus diseases due to invasion

• Pneumonia - rare cause, but severe
• Empyema - pus in pleural space
• Osteomyelitis - bone seeded from blood or by
  trauma, surgery
• Acute endocarditis
• Septic arthritis

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S. aureus skin infections

• Folliculitis
• Furuncle - sweat/sebaceous glands
• Carbuncle - subQ invasion, systemic illness
• Impetigo
• Wound infections
• cellulitis

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S. aureus

• Dx
• Coagulase
• Golden colonies
• Rx tricky, lots of resistance
• Methicillin - resistant to ? lactamase-resistant
  drugs (ex. dicloxacillin)
• Vancomycin resistance emerging

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S. epidermidis

• Coagulase -
• Nosocomial infections
• Catheters, IV lines
• Prosthetic joints
• endocarditis

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S. saprophyticus

• Coagulase -
• Urease
• UTIs in healthy women

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Question 6

• Acute rheumatic fever is a complication of a
  throat infection caused by
• Strep agalactiae
• Staph warneri
• Enterococci
• Viridans strep
• Strep pyogenes

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Question 6

• Acute rheumatic fever is a complication of a
  throat infection caused by
• Strep agalactiae
• Staph warneri
• Enterococci
• Viridans strep
• Strep pyogenes

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Question 7

• Newborns that have evidence of pneumonia and
  sepsis, with or without meningitis, are most
  likely infected with
• Group B strep
• Staph epidermidis
• Staph aureus
• Staph saprophyticus
• Strep pneumo

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Question 7

• Newborns that have evidence of pneumonia and
  sepsis, with or without meningitis, are most
  likely infected with
• Group B strep
• Staph epidermidis
• Staph aureus
• Staph saprophyticus
• Strep pneumo

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Corynebacterium diphtheriae

• G bacillus
• Obligate aerobe
• Normal flora of skin, nasopharynx
• Transmitted by respiratory droplet, skin contact
• Diphtheria toxin
• A subunit ADP ribosyl transferase
• inactivates translation factor EF-2
• Inhibits host protein synthesis
• Damages heart, neuronal cells

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C. diphtheriae

• Respiratory diphtheria
• Pharyngitis, malaise, fever
• Pseudomembrane - grayish, adheres to epithelia
• Colonization site
• Complications breathing obstruction, arrhythmia,
  myocarditis, coma
• Cutaneous diphtheria
• Ulceration, superinfection

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Diphtheric membrane
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C. diphtheriae

• Dx Tinsdales - K-tellurite agar
• Rx
• Antitoxin inactivates circulating toxin give
  early, as once internalized cell death is
  inevitable
• Antibiotics to eradicate infection
• Immunization
• Toxoid vaccine (inactivated)

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Bordatella pertussis

• G- coccobacilli
• Strict aerobe
• Always pathogenic (not normal flora)

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B. Pertussis virulence

• Pertussis toxin 5B1A structure
• Toxic subunit - ADP ribosyl transferase
• Targets Gi, deregulates adenylate cyclase
• Get increase in mucus production
• Adenylate cyclase/hemolysin 1B1A
• Lyses RBCs, messes up phagocytosis
• Tracheal cytotoxin
• Peptidoglycan monomer
• Targets ciliated epithelial cells -gt ciliostasis
• Responsible for cough

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Pertussis or whooping cough

• Incubation 7-10 days
• Catarrhal stage like common cold
• Paroxysmal stage 1-2 weeks
• Spasmotic coughing, vomiting
• Convalescent phase 2-4 weeks
• Gradual decrease in coughing
• Regeneration of respiratory epithelium
• Complications pneumonia, hypoxia, seizures

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B. pertussis

• Dx Bordet-Gengou medium
• Regan-Lowe transport medium
• Rx
• Supportive, antibiotics
• Acellular subunit vaccine

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H. flu
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Haemophilus influenzae

• G- bacillus
• Facultative
• Non-encapsulated strains - normal nasopharyngeal
  flora

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H. flu virulence

• Antiphagocytic capsule
• Type b is most virulent
• Endotoxin (LPS)
• Induces immune response, cytokine release
• Impairs ciliary function

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H. flu type b disease

• Meningitis
• Used to be main cause in kids
• Epiglottitis
• Cellulitis
• Septic arthritis

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H. flu

• Dx
• Culture on chocolate agar
• Latex agglutination (capsular antigen)
• Rx
• Antibiotic prophylaxis for contacts
• Vaccine
• Type B polysaccharide conjugated to protein

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Non-invasive H. flu

• Capsule types other than b
• Acapsular strains
• Otitis media
• Sinusitis
• Bronchitis in chronic pulmonary disease patients

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Question 8

• The mechanism of which of the following toxisns
  is ADP-ribosylation of EF2?
• Pertussis toxin
• Tracheal cytotoxin
• Streptolysin O
• Adenylate cyclase toxin
• Diptheria toxin

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Question 8

• The mechanism of which of the following toxisns
  is ADP-ribosylation of EF2?
• Pertussis toxin
• Tracheal cytotoxin
• Streptolysin O
• Adenylate cyclase toxin
• Diptheria toxin

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