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Streptococcus pneumoniae Staphylococci (Gram positive cocci) Lecture 38

Streptococcus pneumoniae Staphylococci (Gram positive cocci) Lecture 38. Faculty: Dr. Alvin Fox. S. pneumoniae diplococci Pneumococcus autolysin bile solubility test optochin susceptibility capsule Quellung reaction Polyvalent vaccine. Staphylococcus aureus - coagulase (+)

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Streptococcus pneumoniae Staphylococci (Gram positive cocci) Lecture 38

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  1. Streptococcus pneumoniaeStaphylococci(Gram positive cocci)Lecture 38 Faculty: Dr. Alvin Fox

  2. S. pneumoniae diplococci Pneumococcus autolysin bile solubility test optochin susceptibility capsule Quellung reaction Polyvalent vaccine Staphylococcus aureus - coagulase (+) - MRSA (methicillin resistant S. aureus) - opportunistic diseases - food poisoning/enterotoxins - toxic shock syndrome/toxic shock toxin - exfoliative toxin/scalded skin syndrome - α, β, γ and δ cytotoxins - leucocidin - lipase - hyaluronidase - protein A - coagulase (–) - Staphylococcus epidermidis - Staphylococcus saprophyticus KEYWORDS

  3. S. pneumoniae

  4. S. pneumoniae • leading cause of pneumonia • particularly young and old • member normal flora, nasopharynx • replication and spread after damage to upper respiratory tract (e.g. after the flu) • bacteremia • meningitis • middle ear infections (otitis media) - children

  5. S. pneumoniae • α hemolytic • pneumolysin • degrades red blood cells under aerobic conditions • grows well on sheep blood agar • no group antigen

  6. Diagnosis - spinal fluid • direct Gram staining • detection of capsular antigen

  7. Autolysis – identification after growth lipoteichoic acid autolysin Bile teichoic acid -choline peptidoglycan autolysin Cell membrane

  8. C polysaccharide • Teichoic acid (C polysaccharide) • precipitates in serum • binds C-reactive protein

  9. Identification optochin resistant optochin sensitive

  10. Capsule • prominent • virulent strains • anti-phagocytic • carbohydrate antigens • highly variable among strains • numerous serotypes

  11. Capsular vaccine • Immunity • serotype specific • to eradicate the organism in normal flora • Vaccine • a few major serotypes (polyvalent) • Vaccination or the susceptible population • young children • elderly • Immunization • major serotypes susceptible to change • population monitoring essential

  12. Quellung reaction • using antisera • capsule "fixed" • visible microscopically

  13. Pathogenesis • Teichoic acid • complement activation • large numbers of inflammatory cells at infection site

  14. Therapy • S. pneumoniae • most strains susceptible to penicillin • resistance is common

  15. STAPHYLOCOCCI • Gram positive • Facultative anaerobes • Grape like-clusters • Catalase positive • Major components of normal flora • skin • nares

  16. Staphylococcus aureus

  17. One of commonest opportunistic infections, both hospital and community acquired: • pneumonia • osteomyelitis • septic arthritis • bacteremia • endocarditis • abscesses/boils • other skin infections

  18. Antibiotic therapy • Resistance to penicillin • penicillinase • Resistance to methicillin • modified penicillin binding protein • methicillin resistant S. aureus (MRSA) • Vancomycin • current drug of choice • resistance observed but uncommon at this time

  19. Hospital infection control • MRSA now such a problem • monitoring by PCR of nasal swabs • eradication • antibiotics • whole body antisepsis

  20. Food poisoning • not an infection • food contaminated by humans • growth of bacteria • production of enterotoxin • onset and recovery both occur within few hours

  21. Food poisoning • Vomiting • nausea • diarrhea • abdominal pain

  22. Toxic shock syndrome.

  23. Toxic shock syndrome • fever • rash • desquamation • vomiting • diarrhea

  24. Toxic shock syndrome • Toxic shock toxin • Dissemination • Organism • no dissemination

  25. S. aureus • babies • scalded skin syndrome • exfoliatin

  26. Lytic exotoxins: • αtoxin • β toxin (sphingomyelinase C) • γtoxin • δtoxins • detergent-like • leucocidins

  27. Protein A inhibits phagocytosis PHAGOCYTE Fc receptor Protein A immunoglobulin BACTERIUM

  28. Spread • tissue-degrading enzymes • lipase • hyaluronidase

  29. Identification • Sheep blood agar • β hemolytic • yellow pigmented(aureus) • mannitolfermentation • coagulase-positive • phage-typing, rarely performed

  30. Staphylococcus epidermidis • major member, skin flora • opportunistic infection • - less common than S.aureus • nosomial infections • shunts, catheters • artificial heart valves/joints

  31. Identification • Sheep blood agar • non-hemolytic • Non-pigmented • Does not ferment mannitol • Coagulase negative

  32. Several other coagulase negative staphylococcal species • common on human skin • some species cause opportunistic infection

  33. Staphylococcus saprophyticus • urinary tract infections • this coagulase-negative species (and others) • not usually differentiated from S. epidermidis

  34. Summary Figure (Identification Scheme) Note: S. viridansis ALPHA hemolytic and negative for all the tests below GRAM POSITIVE COCCI Catalase - + Streptococcus (pairs & chains) Staphylococcus (Clusters) Hemolysis/Test Coagulase - + + BETA: Bacitracin S. pyogenes (group A) S. aureus S. epidermidis + CAMP/ Hippurate S. agalactiae (group B) Beta hemolytic Non-hemolytic + mannitol mannitol ALPHA: Optochin /Bile Solubility S. pneumoniae yellow white + + GAMMA OR ALPHA: Bile Esculin 6.5% NaCl Group D Enterococcus - + Bile Esculin 6.5% NaCl Group D Non- Enterococcus

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