Staphylococcus and Its Virulence Factors

Staphylococcus

• Spherical, non-motile bacteria that form grape-like clusters
• Gram-positive cocci
• Catalase positive
• Facultative anaerobes
• Normal inhabitants of skin and mucous membranes
• Can ferment glucose except S. saprophyticus

Staphylococcus aureus

• Primary pathogen of the genus
• Found in anterior nares of 20-30% of humans
• Produces superficial to systemic infections
• Can produce various virulence factors, including toxins and enzymes

Staphylococcus aureus Virulence Factors

• Enterotoxins: Heat-stable exotoxins that cause food poisoning and diarrhea
  • Toxins A-E and G-I (eight total)
  • Toxins A, B, and D are the most common causes of food poisoning
  • Toxins B, C, and sometimes G and I are associated with toxic shock
• TSST-1 (toxin F): A superantigen that causes toxic shock syndrome
  • Associated with tampon use
  • Produced by phage group 1
  • Majority of cases of menstruating-associated TSS are due to TSST-1
• Exfoliative toxins (epidermolytic toxins): Cause sloughing of the skin and are associated with:
  • Scalded skin syndrome (SSS) or Ritter’s disease
  • Bullous impetigo
• γ-Hemolysin (Leukocidins): Destroy leukocytes (white blood cells)

Coagulase Test

• Used to differentiate Staphylococcus species
• Enzyme coagulase produced by some Staphylococci
• Coagulase positive Staphylococci form clots in plasma
• Coagulase negative Staphylococci do not form clots

Coagulase Positive Staphylococci

• S. aureus: Human pathogen
• S. delphini, S. intermedius, S. hyicus, S. schleiferi: Animal pathogens

Coagulase Negative Staphylococci

• S. epidermidis: Hospital-acquired infections
• S. saprophyticus: UTIs in young, sexually active females
• S. haemolyticus: Infections in wounds, septicemia, UTIs, and native valve infections

Micrococcus

• Micrococcus luteus: Non-pathogenic
• Gram-positive
• Catalase positive
• Coagulase negative

General Characteristics of Staphylococci

• Morphology: Creamy, white, or light gold colonies. Some produce β-hemolysis
• Appearance: Buttery looking after incubation for 18-24 hours
• Other Characteristics: Non-motile, non-spore forming, non-encapsulated
• Aerobic or Facultative Anaerobic: One exception is S. saccharolyticus (obligate anaerobe)

Media for Growing Staphylococci

• Mannitol Salt agar (MSA): Golden yellow pigments produced by some Staphylococci
• K tellurite medium: Jet-black colonies
• Blood Agar Plate (BAP): Beta-hemolytic activity visible

Explore the fascinating world of Staphylococcus bacteria, focusing specifically on Staphylococcus aureus and its various virulence factors. This quiz covers key characteristics of these bacteria, their role as pathogens, and the toxins they produce. Test your knowledge on their impact on human health and associated infections.