1. General microbiology and sterilization
2. Immunology and infection control
3. Bacteriology
4. Virology, mycology, and parasitology
5. Hospital-acquired infections and specimen collection
6. Physiotherapy-relevant infections, such as TB, wound infection, and hepatitis

1. General microbiology and sterilization
2. Immunology and infection control
3. Bacteriology
4. Virology, mycology, and parasitology
5. Hospital-acquired infections and specimen collection
6. Physiotherapy-relevant infections, such as TB, wound infection, and hepatitis

Staphylococcus - Short Note for BPT 2nd Year

Important species

Staphylococcus aureus

Morphology and culture

• Gram-positive cocci in clusters
• Catalase positive and coagulase positive
• Golden-yellow colonies on culture media due to pigment production
• Grows on mannitol salt agar and ferments mannitol, turning the medium yellow.
• Normal colonizer of skin and anterior nares.

Virulence factors

1. Protein A: Binds the Fc part of IgG and prevents opsonization and phagocytosis.
2. Coagulase: Produces fibrin clot around bacteria, helping them evade host defense.
3. Hemolysins and leukocidins: Cause tissue and leukocyte damage.
4. Hyaluronidase, staphylokinase, lipase, DNase: Help spread through tissues.
5. Exfoliative toxin: Causes scalded skin syndrome.
6. Enterotoxin: Causes food poisoning.
7. TSST-1: Causes toxic shock syndrome.

Diseases caused by S. aureus

• Folliculitis
• Furuncle (boil)
• Carbuncle
• Impetigo
• Cellulitis
• Abscesses
• Wound and postoperative infections
• Osteomyelitis
• Septic arthritis
• Pneumonia, especially following influenza
• Bacteremia and septicemia
• Acute infective endocarditis

• Food poisoning: Sudden nausea, vomiting, abdominal cramps, usually within 1 to 6 hours after eating contaminated food. It is caused by preformed enterotoxin.
• Toxic shock syndrome: Fever, hypotension, diffuse rash, and multiorgan involvement. Associated with TSST-1.
• Staphylococcal scalded skin syndrome: Mainly infants and young children; exfoliative toxin causes peeling of superficial skin.

Laboratory diagnosis

• Specimens: Pus, wound swab, blood, sputum, urine, or body fluid, depending on infection.
• Gram stain: Gram-positive cocci in grape-like clusters, often with pus cells.
• Culture: Blood agar, nutrient agar, and mannitol salt agar.
• Catalase test: Positive.
• Coagulase test: Positive in S. aureus.
• Antibiotic susceptibility testing: Essential, especially to identify MRSA.

Treatment and prevention

• Drainage is important for abscesses and localized pus collections.
• Antibiotics should be selected according to culture and sensitivity.
• Methicillin-sensitive S. aureus is treated with suitable anti-staphylococcal beta-lactam therapy where clinically appropriate.
• MRSA requires agents active against MRSA, chosen according to infection site, severity, and local susceptibility data.
• Prevent spread by hand hygiene, proper wound care, aseptic technique, cleaning shared equipment, and avoiding sharing towels or personal items.

Coagulase-negative staphylococci

Staphylococcus epidermidis

• Normal skin flora.
• Produces biofilm/slime layer, allowing adherence to foreign material.
• Causes infections of:
  • IV catheters
  • Prosthetic heart valves
  • Prosthetic joints
  • CSF shunts
• Important cause of hospital-acquired infection.

Staphylococcus saprophyticus

• Causes acute UTI, especially in young women.
• Coagulase negative.
• Novobiocin resistant, which helps differentiate it from S. epidermidis.

Key differentiating table

One-line exam conclusion