Staphylococcus

• Staphylococci are gram positive, spherical cells in grape like irregular clusters
• Pyogenic infection

  • Boils
  • Carbuncles
  • Wound infections
  • Abscess
  • Impetigo
  • Mastitis
  • Septicemia
  • Osteomyelitis
• Staphylococcus has at least 40 species
• Staphylococcus aureus, staphylococcus epidermidis, staphylococcus lugdunensis, staphylococcus saprophyticus are most frequently encountered species
• Staphylococcus aureus is coagulase positive and a major pathogen for humans
• Staphylococcus haemolyze blood, coagulate plasma and produce extracellular enzymes and toxins
• Coagulase negative staphylococci are normal human microbiota
• 75% of infection caused by coagulase negative are due to Staphylococcus epidermidis, Staphylococcus lugdunensis, Staphylococcus warneri, Staphylococcus hominis
• Pyogenic infections include:

  • Boils
  • Carbuncles
  • Wound infections
  • Abscesses
  • Impetigo
  • Mastitis
  • Septicemia
  • Osteomyelitis
• Toxin mediated infections consist of:

  • Scalded skin syndrome
  • Toxic shock syndrome
  • Food poisoning
• Systemic infections involve:

  • Pneumonia
  • Empyema
  • Meningitis
  • Endocarditis
• Staphylococci grow readily on most bacteriologic media under aerobic or microaerophilic conditions
• They grow most rapidly at 37°C but form pigment best at room temperature (20-25 °C)
• S. aureus usually forms gray to deep golden yellow colonies
• S. epidermidis colonies usually are gray to white on primary isolation
• No pigment is produced anaerobically or in broth
• Peptostreptococcus and Peptoniphilus species, which are anaerobic cocci, often resemble staphylococci in morphology
• Staphylococci produce catalase
• Staphylococci produce lactic acid but not gas
• Staphylococci are relatively resistant to drying and heat (they withstand 50°C for 30 minutes)
• β-lactamase production is common in Staphylococci, which makes them resistant to many penicillins
• Staphylococcus is resistant to nafcillin, methicillin, and oxacillin, and this resistance is independent of β-lactamase production
• Plasmid-mediated resistance in Staphylococci includes tetracyclines, erythromycins, and aminoglycosides
• "Tolerance" in Staphylococci means that they are inhibited by a drug but not killed by it
• Staphylococci are catalase positive
• S.aureus are resistant to many antibiotics

  • Penicillin ( PRSA ) *resistant
  • Metacillin ( MRSA )
  • Vancomycin ( VRSA )
  • Glycopeptide ( GISA ) *intermediate
• Clumping factor is responsible for adherence of organisms
• Clumping factor induce strong immunogenic response and is the focus of vaccine efforts
• Source of infection

  • Patient and carrier
• Staphylococci are found on clothing, bed linens, and other formites
• Staphylococci survive for several months in dried pus and sputum
• Mode of transmission

  • Contact transmission
  • Airborne transmission
  • Cross infection
• Non-pathogenic, non-invasive staphylococci are coagulase negative and non-haemolytic and not produce suppuration
• Toxic shock syndrome is caused by TSST-1
• Bullous exfoliation, the scalded skin syndrome is caused by the production of exfoliative toxins
• It is not possible to distinguish S.epidermidis and S.aureus on smear
• Coagulase negative strain is tested by DNase test
• Two coagulase test

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