Microbiology Staphylococcus Overview

Gram Positive Cocci

• Gram-positive cocci are spherical bacteria arranged in clusters.
• They are non-spore forming, non-motile, and usually non-encapsulated.
• Key species include:
  • Staphylococcus aureus: Coagulase-positive, significant pathogen.
  • Coagulase-negative staphylococci (CNS): S. epidermidis and S. saprophyticus.
• Resistance:
  • S. aureus and other Micrococcaceae are highly resistant, often viable for 3-6 months.
  • Many strains can grow with 10% NaCl.

Staphylococcal Toxins and Enzymes

• Staphylococcus aureus virulence is due to various toxins and enzymes.
• Toxins:
  • Cytolytic toxins (e.g., alpha, beta, gamma, delta hemolysins, leukocidin).
  • Enterotoxins (cause food poisoning).
  • Toxic Shock Syndrome Toxin-1 (TSST-1).
  • Epidermolytic toxins (cause scalded skin syndrome).
• Enzymes:
  • Coagulase.
  • Catalase.
  • Hyaluronidase.
  • Fibrinolysin.
  • Lipases.
  • Nucleases.
  • Penicillinase.

Staphylococcal Diseases

• Cutaneous infections: Boils, furuncles, carbuncles, impetigo, wound infections.
• Deep infections: Osteomyelitis, periostitis, tonsillitis, pharyngitis, sinusitis, other organ abscesses, septicemia.
• Toxin-mediated diseases:
  • Food poisoning (faulty food with S. aureus containing toxin).
  • Toxic shock syndrome (TSS) (associated with tampon use).
  • Scalded skin syndrome

Coagulase-Negative Staphylococci

• S. epidermidis and S. saprophyticus are commonly found on human skin.
• Opportunistic pathogens, causing infections in immunocompromised individuals, often associated with foreign bodies.
• Urinary tract infections and other infections, such as endocarditis, are connected to these species.
• Resistance to novobiocin distinguishes S. saprophyticus from S. epidermidis.
• These organisms don't ferment glucose anaerobically.

Methicillin-Resistant Staphylococcus aureus (MRSA)

• MRSA isolates are resistant to methicillin and other beta-lactam antibiotics.
• Frequent in hospitals and community settings due to overuse of antibiotics.
• Important cause of infections in individuals with compromised immune systems.

Treatment and Control

• S. aureus: Benzylpenicillin (if sensitive), oxacillin, cloxacillin, Vancomycin, Glycopeptides (for severe infections).
• Control:
  • Drain abscesses, prevent infection spread (e.g via hand washing).

Streptococcus Species

• Major bacterial species include:
  • Streptococcus pyogenes (Group A).
  • Streptococcus agalactiae (Group B).
  • Streptococcus Pneumoniae
  • Viridans streptococci.
  • Enterococcus faecalis (Group D).

Streptococcal Diseases

• Streptococcus pyogenes illnesses: Sore throat, scarlet fever, rheumatic fever, acute poststreptococcal glomerulonephritis (AGN), skin and soft tissue infections.
• Streptococcus agalactiae (Group B Strep): Neonatal sepsis, pneumonia, meningitis.

Pneumococcal Diseases

• Streptococcus pneumoniae: Pneumonia (lobar, broncho), meningitis, bacteremia.