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

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 Lancefield’s 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) • Host’s 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 cell’s 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 1800’s, 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 rate>30%

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 • Bright’s 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