Human Diseases

1

• Human Diseases
• Caused Primarily by Gram-Positive and
  Gram-Negative Bacteria  
• The Airborne Diseases Part II

2
Streptococci
3

• General features
• Cause variety of serious infections often leading
  to sequelae
• Secondary complications arising during
  convalescent stage of infection
• AKA nonsuppurative disease (inflammation in an
  organ that was NOT infected by the streptococcus)
• Cocci spherical form pairs or chains during
  cell division
• Nonmotile ? no flagellae

4

• Fastidious
• Require enriched medium for growth
• Amino acis
• Purines or pyrimidines
• B vitamins
• Laboratory culture
• Complex, undefined medium
• Peptones, glucose, salts, meat infusions and 5
  defibrinated blood agar (blood agar plates)

5

• Most streptococci aerotolerant anaerobes
• Some obligately anaerobic (female genital
  tract)
• Sugar is fermented to lactic acid under aerobic
  and anaerobic conditions (homolactic acid
  fermenters)
• Aerobic respiration is not possible
• Lack the capability to syntesize heme (prosthetic
  group of cytochromes)
• No electron transport using oxygen as TEA

6

• Lack catalase
• Therefore hydrogen peroxide can increase to toxic
  levels when grown aerobically
• Blood agar minimizes this effect RBC provide
  catalase source
• Hemolysins
• Toxin secreted by streptococcus that results in
  lysis of RBC
• Useful in determining streptococcal species
• Alpha, beta or gamma hemolysis

7

• Alpha hemolysis
• Incomplete brown/green halo around CFU
• Not lysed
• Reduced product of hemoglobin
• Examples
• Viridans streptococci
• S. parasanguis
• S. mutans
• S. pneumoniae
• Some Group D streptococci (Enterococci and
  non-enterococci)
• Both can cause UTI and subacute bacterial
  endocarditis

8

• Beta hemolysis
• Complete hemolysis
• Clear zone around CFU
• RBC are completely lysed
• Streptolysin S (serum extractable and stable in
  air)
• Streptolysin O (oxygen sensitive)
• Anaerobic conditions needed to see effect
  mediated by this toxin
• Examples
• S. pyogenes
• S. agalactiae

9

• Gamma hemolysis
• No hemolysis at all
• Group N streptococci
• Lactic streptococci
• Some Enterococci Group D
• 45oC, 6.5 NaCl, pH 9.6!!!!!!!

10

• Classification
• Biochemical and antigenic properties used to
  divide streptococci into different groups and
  subtypes
• Rebecca Lancefield developed a Group
  Classification scheme

11

• Used for all streptococci except the viridans
  group and S. pneumoniae based on a soluble
  carbohydrate antigenic (C carbohydrate) present
  in the cell wall ? Letter Code (A ? O no I or J)
• C carbohydrate extractable with formamide or acid
  treatment with heating
• All streptococci except viridans posses the C
  carbohydrate (even S. pneumoniae but not used in
  Lancefield groupsing)
• Groups of streptococci based on Lancefields
  system can be linked to particular habitats

12

• Species within groups (A?O) can be further
  subdivided into specific types based on other
  antigenic properties
• Examples
• A second cell wall protein called M protein is
  present on some Group A streptococci but no all
  members (60 different types!) ? Confer type
  specific immunity
• Carbohydrates other than C carbohydrate

13

• Group A beta-hemolytic streptococci
• S. pyogenes
• General features and virulence characteristics
• Majority of streptococci responsible for acute
  infections belong to Group A
• Associated with sequelae complications
• Erythema nodosum skin
• Rheumatic fever heat and joints
• Acute glomerulonephritis kidney
• 60 different subtypes based on M protein
  differences

14

• Virulence factors
• M protein virulence factor
• Fimbriae of M protein stick out of the capsule
• Antiphagocytic
• Blocks alternate pathway of C activation
• No C3b made ? therefore no opsonization
• Superantigen characteristics
• Stimulates T cells without processing requirements

15

• Generates type-specific immunity
• Only antibodies specific for particular M protein
  can bind and mediate opsonization
• Capsule made of hyaluronic acid (present in
  connective tissue, therefore we are tolerant)

16

• Adhesins
• Enagle streptococci to bind to host cell
  glycoproteins
• Streptococcal F protein
• Lipoteichoic acid
• Both bind fibronectin of ECM
• Streptokinase
• Secreted ? induces fibrinolysis which enhznces
  dissemination and prevents formation of fibrin
  barier
• Connective tissue and basement membranes
  hydrolyzed

17

• Hyaluronidase
• Spreading factor
• Made only if capsule is absent (capsule is made
  of hyaluronic acid)
• Hosts hyaluronic acid degraded
• Intercellular spaces opened
• Dissemination

18

• Streptodornase
• DNAses 4x
• Decrease viscosity in areas of cell lysis
• Promote dissemination
• Antibodies made during infection important in
  diagnosis

19

• Streptolysin O (oxygen sensitive)
• Binds to cholesterol and other sterols of host
  cell membrane
• Toxin oligomers generated
• Transmembrane pores formed
• Cytotoxicity results
• Lysosomal enzymes released into host cells
  cytosol degranulation)
• Binds circulating IgG
• Immune complexes formed
• Complement activated
• Tissue damage

20

• Inhibits recruitment of leukocytes (suppresses
  chemotaxis)
• Anti-streptolysin O antibody titers can assist n
  diagnosis of sequelae (Rheumatic fever and acute
  glomerulonehritis)

21

• Streptolysin S
• Only 28 amino acids
• Oxygen stable
• Inhibits chemotaxis and phagocytosis
• Beta hemolysis of RBC and kills leukocytes
• Not antigenic (too small??)
• C5a peptidase
• Removes 6 amino acids from COOH end of C5a
• Interferes with binding to PML C receptors for
  C5a
• Inhibits chemotaxis

22

• Pyrogenic exotoxins A, B (aka Spe A,B) three
  serotypes
• SpeA superantigen (Sag)
• T cell cytokines damage blood vessls
• Fluid loss
• Tissue damage
• Induce macrophage to syntesize TNF-alpha Il-1
• Serotype A associated wiith scarlet fever and
  rheumatic fever

23

• SpeB Exotoxin B
• Cysteine protease
• Destroys tissue rapidly
• Associated with necrotizing fasciitis (flesh
  eating bacteria)
• Erythrogenic toxins rash
• Leukocidins leukocyte degranulation and death

24

• Pathogenicity of Group A streptococci
• Streptococcal pharyngitis STREP THROAT
• Most common disease cause by these bacteria
• Acute
• Tonsils and pharynx inflamed (edematous
  fluid-filled)
• Inflammatory response with lysis of erythrocytes
  and leucocytes
• Enlarged cervical lymph nodes
• Fever
• Lasts only 5 days (self limiting)
• Host makes antibodies to M protein

25

• May spread to middle ear or meninges (rare)
• Can cause pneumonia if present during a viral RTI
  (influenza or measles)
• Spread through respiratory tract secretions from
  infected people or by contaminated food source
  (infected food handler lesions on hands)
• Treatment is with penicillin, primarily to
  minimize the possibility of subsequent rheumatic
  fever and glomerulonephritis

26

• Scarlet fever (Scarlatina)
• Caused by erythrogenic toxin-positive Group A
  streptococci ( pyrogenic exotoxin A, SpeA SAg)
• Caused by a lysogenic bacteriophage
• Usually begins as sore throat, then toxin
  disseminates ? diffuse rash (if hypersensitivity
  reaction ensues or in absence of neutralizing
  antibodies)
• Inasion of bacteria into the bloodstream
• Fever
• Strawberry-colored tongue

27

• Skin shedding
• Immunosuppression (due to effects of Sag)
• Prevalent in mid 1800s, reemergence on the rise
• If invasive, can trigger a streptococall toxic
  shock-like syndrome )TSLS)
• Muppeteer Jim Hensen died of pneumonia produced
  by streptococcal infection
• Decreased BP
• Organ failure
• Very high fever
• Mortaity rategt30

28

• Necrotizing fasciitis flesh eating bacteria
• Infection of planes of tissue under the skin,
  especially in the fascia
• Necrosis of skin owing ot destruction of blood
  vessels and nerve cells
• Rapid spread, 50-80 mortality rate
• Amputation often necessary
• Tissue must be removed down to the muscle layer

29

• Non-respiratory infections caused by Group A
  streptococcus
• Streptococcal impetigo (pyoderma)
• Superficial skin infection characterized by
  formation of small vesicles that develop into an
  amber crust
• Often nephritogenic (affects kidneys) ? resulting
  in acute glomerulonephritis
• Low socioeconomic environments
• Crowded housing conditions
• Superficial cutaneous infection commonly seen in
  children

30

• Puerperal sepsis
• Postpartum (following delivery of baby) uterine
  infection
• Wound infections
• Erysipelas acute infection of dermis, reddish
  patches
• Often in combination with anotehr aobligate
  anaerobe of normal flora of gastrointestinal and
  genitourinary tracts (e.g. bacteroids)

31

• Cellulitis
• Diffuse, spreading infection of subcutaneous
  tissue characterized by redness and swelling

32

• Diagnosis of Group A Streptococci
• Tentative identification if beta hemolytic growht
  on blood agar plate (24 hours, 37oC)from throat
  swab
• Gram positive cocci chains
• Colonies small, dense/compact and dull

33

• Specific serological identification
• Latex bead agglutination
• Anti-group A carbohydrate antibody bound to beads
• Carbohydrate must first be extracted froom
  loopful of culture (from cfu or pharyngeal throat
  swab)
• Positive agglutination confirms Group A
  streptococci
• Bacitracin discs
• Used to differentiate between Group A and Group B
  streptococci
• Both beta hemolytic
• Group A streptococci are sensitive (bacitracin
  sensitivity)

34

• Fluorescence labeled antibodies specific for C
  carbohydrate
• Non-suppurative sequelae complications
• Immunological tests
• High titer of anti-streptolysin O antibody
• High titer of anti-streptodornase antibody
• Suggestive of recent beta hemolytic strep
  infection

35

• Late nonsuppurative sequelae complications of
  Group A Strep infections Immunological
  Aftermath Caused by Cross-Reactivity
• Poststreptococcal diseases - onset is one to four
  weeks after an acute streptococcal infection
• Erythema nodosum
• Skin lesions following some Group A strep
  infections
• Toxic agent???? Streptococcul cell wall???

36

• Rheumatic fever
• Heart and joints
• Joints are unaffected after recovery but
  permanent heart damage can occur
• Cross reactivity between myocarial and
  streptococcal components (M protein)
• M protein deposition in heart and joints
• Cross reactive antigen of streptococcus and heart
  tissue
• Host antibodies can bind to self itssue
• Immune complexes, complement activation, C5a,C3a,
  tissue damage and inflammation

37

• Superantigen effect of M protein
• Production of streptococcal cardiotoxin
• Recent resurgence of actue rheumatic fever cases
• Still very prevalent in developing nations
• 25-40 of cardiovascular disease linked to RF
• Involves the heart valves, other parts of the
  heart joints, subcutaneous tissues and central
  nervous system
• Occurs primarily in children ages 6 to 15 years
  old
• Therapy is directed at decreasing inflammation
  and fever, as well as controlling cardiac
  symptoms and damage

38

• Acute glomerulonephritis
• Less frequent than Rheumatic fever
• Nephrotoxic action of streptococcal toxins
• Cross reactivity with streptococcal antigens in
  glomeruli
• Cross react with glomerular basement membranes of
  the kidney (?)
• Immune complexes, complement activation, C3a,C5a,
  inflammation and tissue destruction
• Bloody urine
• Hypertension
• Brights disease
• May spontaneously heal or may become chronic
• Possibly a kidney transplant or lifelong renal
  dialysis may eventually be necessary
• A type III hypersensitivity

39

• Treatment and prevention
• Penicillin 8-10 days (cidal)
• Rhematic fever prevented but not always acute
  glomerulonephritis
• Erythromycin for penicillin-allergic patients
• Prevention of re-infection important in those who
  have had Rheumatic fever (low dose penicillin
  daily for many years)
• Carriers 5010 (up to 30 depending on season)
• Therefore difficult t control spread of these
  bacteria

40
Streptococcus pneumoniae
41

• General features
• Pneumococcus
• Alpha-hemolytic
• Lancet-shaped pairs or short chains
• Gram positive, nonmotile, non-spore forming
• Encapsulated forms virulent
• Primary virulence factor Multiplies quickly in
  alveolar spaces

42

• Choline required growth factor (used as part of
  teichoic acid)
• Lack cytochromes and catalase
• Require complex, enriched growth medium
• Part of normal flora
• Nasopharynx
• Therefore considered an endogenous infection
  (opportunist)
• From here the pneumococcus can enter the blood
  stream

43

• Associated with predisposing factors
• Diabetes
• Alcoholism
• Viral infection of URT
• Injury to respiratory tract

44

• Classification
• Polysaccharide capsule ? 80 different antigenic
  types (serological types)
• C carbohydrate type specific M protein (but
  this M protein is not antiphagocytic)
• Does not fit into the Lancefield scheme
• Three common infections
• Pneumonia
• Meningitis
• Otitis media

45

• Pneumonia
• Secreted pneumolysin believed to play a role in
  inhibiting antimicrobial properties of
  neutrophils and opsonization
• Binds to cholesterol of host cells
• Cytotoxic for pulmonary endothelial cells
• May be partly responsible for alveolar
  hemorrhages (blood in sputum)
• Capsule
• Protects against phagocytosis virulence factor

46

• Infections most common in conjunction with viral
  URT infection and in unhealthy or older patients
  (bedridden)
• Smokers
• People who have inhaled toxic irritants of URt
• Acute lung inflammation
• If it involves one or more lobes of the lungs
  lobar pneumonia
• Or causes bronochopneumonia in children or
  elderly (more restricted than lobar pneumonia)
• Exudate fills the alveoli ? compromising gas
  exchange and oxygen levels in the blood

47

• Abrupt onset of chills, fever, pleural pain
• Secondary complications
• Can invade the sinuses (3-4-5 of bacterial
  cases), the middle ear and the meninges
• Septicemia, endocarditis (inflammation of heart
  and valves), pericarditis (inflammation of
  membrane around the heart) and empyema (pleural
  cavity infection)
• Anti-capsular antibodies lead to fast recovery

48

• Meningitis
• Second most common cause in adults
• Occurs as complication of pneumonia or sinusitis
  ? dissemination into bloodstream
• Can arise following skull fractures when they
  enter the meninges from the nasopharynx

49

• Otitis media (middle ear infection)
• About ½ of childhood cases of middle ear
  infections due to S. pneumonia
• Only certain types responsible (6,14,19,24)

50

• Diagnosis
• Stain smears of sputum, CSF, blood or cultured
  sample
• Gram positive, encapsulated diplococci or chains
• Bile soluble
• Quellung test
• Capsule specific antibodies capsule swells
• Replaced by more modern reagent omni-anti-serum
  (antibodies to all types of capsular antigens)
• Optochin sensitivity discs (ethyl hydrocuprine
  hydrochloride)
• Inhibitory to S. pneumoniae alpha hemolytic
• Viridan streptococci grows also alpha hemolytic

51

• Treatment and prevention
• Penicillin G, or if sensitive/allergic to
  penicillin G, use cefotaxime, cephalothin or
  erythromycin for pneumonia
• Chloramphenical for meningitis (BBB)
• Vancomycin for penicillin resistant strains

52

• Vaccines
• Pneumovax
• 23 types of capsular polysaccharides
• Suggested for use in
• Splenic disorders/splenectomy
• Sickle cell anemia
• Congestive heart failure
• Diabetes mellitus
• Alcoholism
• The elderly in rest homes
• Young children respond poorly (poor T-independent
  B cells responses)

53
Mycobacterium tuberculosis
54

• Tuberculosis caused by tubercle bacillus
• Extreme variation in the severity of disease
• Mild
• Chronic
• Destruction of pulmonary tissue
• Global health problem
• Estimated 1 x 109 infected (20 of worlds
  population)
• 107 new cases/year
• 3 x 106 deaths/year
• In USA 26,000 new cases/year with 12,000
  deaths/year, associated with AIDS epidemic

55

• General features
• Thin rods, straight or sometimes bent or club
  shaped
• Non-motile, nonsporing, nonencapsulated,
  waxy-acid fast (Ziehl-Neelsen stain using carbol
  fuchsin)
• Beaded or granular intracellular staining
• High lipid and wax content mycolic acid
• Mycolic acids isolated from Mycobacterium have
  60-90 carbon atoms
• Rhodamine/auramine flluorochrome mix binds
  mycolic acid (fatty acids)

56

• Obligate aerobes
• Resistant to drying (sputum in bed linen)
• Simple media requirements, but very slow growing
  (20 hours/division)
• Killed by pasteurization
• Cord factor (trehalose dimycolate)
• Complex fatty acid associated with carbohydrate
• Only found in virulent strains
• Serpentine cords of growth result ? clumps
• Induces TNF alpha (cachectin)

57

• Pathogenicity
• Spread by respiratory droplets and droplet nuclei
• Can remain suspended in air for long periods
• Highly infectious

58

• Primary infection
• Colonization of LRT ? small lesions primary
  complex ? can form tubercles
• Tubercles tiny, hard nodules caused by a
  hypersensitivity response (DTH type IV)
• Granuloma surrounded by fibrous tissue
• Spread to draining lymph nodes
• If tubercle lesion expands ? tissue is damaged
  a cheesy consistency referred to a caseation
  necrosis (caseous lesion)
• After healing calcium deposits and cavities
  develop in the lungs
• Ghon complexes calcified lesions seen in X-rays

59

• If pulmonary vein involved in lesion then the
  bloodstream in invaded
• Lesions develop elsewhere in other organs leading
  to Miliary tuberculosis (tubercles the size of
  millet seeds)

60

• Can also lead to meningitis
• Exudative lesions form early in primary infection
• PMNLs, inflammation, fluid (exudate)
• Dividing within macrophages until TH1 activated

61

• Productive lesions (tubercles) form later on
• Granulomatous lesions
• Giant cells containing tubercle bacilli
  surrounded by a zone of epithelioid cells
• Released to extracellular fluid
• Walled off in the lung
• Contain viable bacteria
• Can survive indefinitely

62

• Reactivation infection
• Arise from walled-off tubercles (hence, not a
  primary infection)
• Infection arises from latency
• These patients would skin test positive

63

• Immunity
• TH1 recognize mycobacterial antigens with MHC
  class II on macrophage surface
• Macrophages are activated by TH1 ? degradation of
  intracellular bacteria in lysosomal compartments
• Once sensitized, a DTH response if exposed
  intradermally to M. tuberculosis antigens (PPD)
  (tuberculin skin test Heath test, Mantoux test,
  Tine test)
• Often bacteria remain alive due to resistance to
  oxidative killing by macrophages

64

• Clinical management (no more sanitariums)
• Two drugs used in combination owing to drug
  resistance
• Primary drugs
• Isoniazid (INH) Rifampin, least toxic, most
  effective, 9 months
• Long treatment required because
• Mycobacteria grow slowly
• Mycobacteria metabolize slowly
• Drug doesnt easily penetrate the fibrotic or
  caseousl lesions
• Secondary drugs
• Pyrazinamide
• Ethanbutol
• Streptomycin
• Three-in-one pill
• INH, rifampin and pyrazinamide (approved by FDA
  in 1994)

65

• Multidrug resistant M. tuberculosis (MDR-TB)
• Resistant to INH and rifampin
• Requirements for more drugs in cocktail (4 or 5
  total)
• High mortality rates
• Noncompliance of drug therapy thought to be
  responsible

66

• Control
• gt20,000 new cases annually in USA, 2500 deaths
• Tuberculin skin test used for early detection
• Indication of whether disease is quiescent or
  active (TDTH response)
• Potential candidates for active disease
• Those in close association with individual
  diagnosed with T.B. (prophylaxis)
• Positive skin test and positive chest X-ray
• Skin tested positive within 2 year period
• Skin tested positive and immunocompromised
• Silicosis, diabetes, transplant patients,
  leukemia, Hodgkins disease
• lt35 years old and skin tested positive

67

• Vaccine
• BCG Bacille Calmette-Guerin (50 protection)
  (bovine strain)
• Vole bacillus (murine strain)
• Not used in USA because of diagnostic value of
  skin test as indicator of recent infection

68

• Diagnosis
• Samples of sputum, urine or gastric washings
  should be stained acid fast stain
• Must also be cultured (several weeks)
• Culture media
• Selective for M.tb oleic acid, albumin,
  penicillin and dyes (malachite green)
• ELISA and PCR hastens I.D.
• Ghon complexes seen on X-ray
• BACTEC and NPT test