STAPHYLOCOCCI

Definition: Staphylococci are a type of gram-positive bacteria that belong to the genus Staphylococcus.
Morphology:
- Cocci in clusters (grape-like clusters)
- Non-motile
- 0.5-1.5 μm in diameter
- Cell wall contains peptidoglycan and teichoic acids
- Spore-forming is not characteristic
Types:
- Staphylococcus aureus (golden colonies)
- Staphylococcus epidermidis (smaller colonies)
- Staphylococcus saprophyticus (coagulase-negative)
- Staphylococcus haemolyticus (coagulase-negative)
Virulence Factors:
- Coagulase (clumping factor)
- Protein A (inhibits phagocytosis)
- Toxic-Shedin (enterotoxins)
- Hemolysins (α, β, γ)
- Exfoliative toxins (epidermolytic toxins)
Pathogenesis:
- Entry through wounds or mucous membranes → Infection spreads to blood (sepsis) or other organs → Production of virulence factors → inflammation and tissue damage
Pathogenesis of Staphylococcus aureus infections:
- Nasal colonization → entry into body through wounds or mucous membranes → Infection spreads to skin, lungs, or other organs → Production of virulence factors → inflammation and tissue damage
Laboratory Diagnosis:
- Gram staining (gram-positive cocci in clusters)
- Biochemical tests (coagulase, catalase, etc.)
- API Staph (identification kit)
- Blood culture (for sepsis)
Clinical Features:
- Skin infections (boils, impetigo, folliculitis)
- Respiratory infections (pneumonia)
- Food poisoning (enterotoxins)
- Septicemia (bloodstream infection)
- Endocarditis (heart valve infection)
Complications:
- Sepsis (bloodstream infection)
- Meningitis (inflammation of meninges)
- Osteomyelitis (bone infection)
- Endocarditis (heart valve infection)
Management:
- Antibiotics (penicillin-resistant strains require alternative antibiotics)
- Drainage of abscesses or boils
- Treatment of underlying conditions (e.g., diabetes, immunodeficiency)
- Vaccination (against certain staphylococcal toxins)

Life Cycle