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Staphylococcus

Staphylococcus. Dr. Jyotsna Agarwal Professor, Dept. of Microbiology K G Medical University, Lucknow. Family: Micrococcaceae Genus: Staphylococcus - derived from Greek “stapyle” (bunch of grapes) Include major human pathogen and skin commensals Micrococcus - skin commensal.

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Staphylococcus

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  1. Staphylococcus Dr. Jyotsna Agarwal Professor, Dept. of Microbiology K G Medical University, Lucknow

  2. Family: Micrococcaceae Genus: Staphylococcus- derived from Greek “stapyle” (bunch of grapes) Include major human pathogen and skin commensals Micrococcus- skin commensal

  3. Staphylococcus: General Characteristics Gram-positive spherical cells (0.5-1.5 mm) in singles, pairs, and clusters Appear as “bunches of grapes” Gram-stained smear of staphylococci from colony

  4. Non motile Non–spore-forming Nonencapsulated Catalase-producing Oxidase: negative Glucose fermenters Primarily aerobic, some facultatively anaerobic Staphylococcus: General Characteristics

  5. Approximately 33 species ~15 species associated with humans Staphylococcus divided into coagulase positive & coagulase negative categories Inhibited by high bile salt concentration Some are ß-hemolytic Colony morphology: buttery looking, cream or white colored Staphylococcus: General Characteristics

  6. S. aureus S. intermedius S. hyicus S. delphini S. schleiferi Coagulase Positive Staphylococci Human pathogens Veterinary pathogens Animal-associated species

  7. Primary pathogen Habitat: anterior nares (carriers) Colonization: axilla, perineum, pharynx Produce superficial to systemic infections Mode of transmission: Pus formation Staphylococcus aureus

  8. Natural history of disease • Usual sites - skin, nasopharynx, perineum • Breach in mucosal barriers - can enter underlying tissue • Characteristic abscesses with Pus • Bacteria liberates toxins-

  9. Due to direct effect of organism Local - skin Deep abscesses Systemic infections Toxin mediated Food poisoning toxic shock syndrome Scalded skin syndrome DISEASES

  10. Pathogen Factors ENZYMES Catalase (counters host defences) Coagulase Hyaluronidase Lipases B lactasamase (antibiotic resistance) TOXINS- enterotoxin, TSST, epidermolytic toxin Virulence Factors of S. aureus

  11. SKIN LESIONS- superficial • Boils • Styes • Furuncles • Carbancles • Wound infections

  12. DEEP ABSCESSSES • Direct / by blood • Can be single / multiple • Eg. - Breast abscess kidney, brain, Osteomyelitis, septic arthritis

  13. TOXIN MEDIATED DISEASES 1. Staphylococcal food poisoning • Due to production of enterotoxins • preformed toxin, heat stable • short incubation period • Milk & milk products

  14. 2. Toxic shock syndrome • High fever, diarrhoea, shock and erythematous skin rash which desquamate • Mediated via ‘toxic shock syndrome toxin’ • 10% mortality rate

  15. 3. Scalded skin syndrome • Disease of young children • Mediated through minor Staphylococcal infection by ‘epidermolytic toxin’ producing strains • Good prognosis

  16. Virulence Factors: Extracellular enzymes Cytolytic Toxins Alpha hemolysin: lyses rbcs, damages plts, causes severe tissue damage ß hemolysin: acts on sphingomyelin in the plasma membrane of rbcs

  17. Virulence Factors: Extracellular enzymes Hyaluronidase: Hydrolyzes hyaluronic acid in connective tissue allowing spread of infection Staphylokinase: fibrinolysin which allows spread of infection Coagulase: virulence marker Lipase: allows colonization

  18. Beta-lactamase or Penicillinase: confers resistance DNase: degrades DNA Protein A: in cell wall, it binds to Fc part of IgG toblock phagocytosis Virulence Factors: Extracellular enzymes

  19. Coagulase-Negative Staphylococci Habitat: skin and mucous membranes Common human isolates S. epidermidis S. saprophyticus

  20. Coagulase-Negative Staphylococci: Staphylococcus epidermidis Virulence factor: “slime” Mode of infection: colonization of medical implants Infections are acquired nosocomially Serious infections among immunosuppressed patients or neonates may occur

  21. Habitat: skin and mucosal membranes of the genitourinary tract Common cause of urinary tract infections in young, sexually active females Coagulase-Negative Staphylococci: Staphylococcus saprophyticus

  22. Microscopic Examination Gram-positive cocci pairs and clusters Numerous polymorphonuclear cells (PMNs) Laboratory Diagnosis: Direct Smear Examination

  23. Laboratory Diagnosis: Cultural Characteristics Colony morphology Smooth, butyrous, white to yellow, creamy Grow well in 18-24 hours S. aureus may produce hemolysis on blood agar S. aureus

  24. Principle: tests for enzyme catalase Drop H2O2 onto smear Bubbling = POS (Staph) No bubbling = Streptococci Identification Tests: Catalase

  25. Cell-bound “clumping factor” converts fibrinogen to fibrin which precipitates on cell causing agglutination Extracellular enzyme “free coagulase” Identification Tests: Coagulase Test • Two methods • Slide test: screens for “clumping factor” • Tube test

  26. Novobiocin Susceptibility Test Test to differentiate coagulase-negative staphylococci from S.saprophyticus from urine samples S. saprophyticus is resistant (top)

  27. Beta-lactam group of antibiotics- (penicillins, cloxacillins, ampicillin, amoxycillin) Beta-lactamase producers treatment of choice Amoxyclavulinic acid or ampicillinn sulbactam combo or methicillin/ oxacillin For methicillin -resistant S. aureus(MRSA) treatment of choice- Vancomycin Antimicrobial Susceptibility

  28. Summary • Characters of Staphylococcus aureus • Enzymes / Toxins • Infections / Diseases • Laboratory diagnosis • Treatment / Abx resistance

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