2. Epidemiology & Transmission
- Source: Colonize Nose (in 30% of people), Vagina (in 5% of women), Sheddding from human lesion and
fomites (towel, lothing)
- Predisposition: Diabetes, IVDU, chronic granulomatous disease
3. Virulence Factor
1. Enterotoxin
o causing food poisoning ( prominent vomiting and watery, non bloody diarrhea).
o Act as superantigen of GIT -> stimulate release of IL-1 and IL-2 from macrophage and helper T cell respectively.
o Fairly heat-resistant, not inactivated by brief cooking
o Resistant to stomach acid and enzyme in stomach and jejunum
2. Toxic shock syndrome toxin (TSST)
o Especially in tampon using menstruating women, individual with wound infection, using nasal packing (to stop
nose bleed)
o Toxin produced by staph aureus in vagina, nose or infected wound
o Toxin enter blood stream -> toxemia . Blood culture do not grow staph aureus
o A superantigen, stimulate release large amounts of IL1, IL2, TNF
4. 3. Exfoliatin
o Cause scalded skin syndrome in children
o Epidermolytic, Act as a protease that cleaves desmoglein in desmosomes -> Separation of epidermis at
granular cell layer
o Localized exfoliatin production -> bullous impetigo
4. Other exotoxins
o Alpha toxin: marked necrosis of skin and hemolysis by causing holes formation in cell membrane ->loss of
low-molecular weight substance from damaged cell.
o P-V leucocidin: pore-forming toxin that kills cell esp WBC by damaging cell membranes. Have role in severe
skin and soft tissue infection, severe necrotizing pneumonia
5. Other enzymes
o Coagulase, fibrinolysin, hyaluronidase, proteases, nucleases, lipases
6. Pyogenic Diseases
1) Skin and soft tissue infection
o Includes abscess, impetigo, furuncles, carbuncles, paronychia, cellulitis, folliculitis, NF, hidradenitis
suppurativa, conjunctiva, eyelid infection, lymphagenitis
2) Septicemia
o Originate from localized lesion (e.g. wound infection) or IV drug abuse
3) Endocarditis
o On normal or prosthetic valves, especially right sided endocarditis (tricuspid valve) in IVDU
4) Osteomyelitis and septic arthritis
o Hematogenous spread from a distant infected focusor introduced locally at a wound site
7. 5) Post surgery wound infection
6) Pneumonia
o In postoperative patients or following viral respiratory infection, especially
influenza
oOften leads to empyema or lung abscess
oMost common cause of nosocomial pneumonia esp in ventilator-associated
pneumonia
oCA-MRSA causing severe necrotizing pneumonia
7. Conjunctivitis
6. Abscess at any organ
oFollowing bacteremia
8. Toxin Mediated Diseases
1. Food poisoning
• Vomiting typically more prominent than diarrhea
2. Toxic shock syndrome
• Characterized by fever, hypotension, diffuse macular sunburn-like rash that goes
on to desquamate; involvement of >3 following organs: liver, kidney, GIT, CNS,
muscle or blood
3. Scalded skin syndrome
• Fever, large bullae, erythematous macular rash.
• Large areas of skin slough, serous fluid exudes, electrolyte imbalance can occur
• Hair and nails can be lost
4. Bullous impetigo
• Caused by localized production of exfoliatin
9. Lab Diagnosis
- Spherical gram-positive cocci arranged in irregular grapelike clusters
- Catalase positive – can survive killing effect of H2O2 within neutrophils
- Coagulase positive – enzyme causes plasma to clot by activate prothrombin to thrombin. Thrombin
catalyzes fibrinogen to form fibrin. Fibrin clot -> wall off bacteria and prevent neutrophils access at
infection site
- Staphyloxanthin pigment production – golden colonies. Inactivating microbicidal effect of superoxides and
other reactive o2 species in neutrophils
- Mannitol salt agar - Ferments mannitol turns agar to yellow
- Hemolyze RBC - by hemolysin. Iron required for growth.
10. Treatment
1. Incision & Drainage
• Sufficient in treating skin abscess (e.g. furuncle)
• Antibiotic only required if signs of systemic infection – Oral trimethoprim-sulfa, IV vancomycin
2. Antibiotics
• >90% strain resistant to penicillin G by producing B-lactamase
-> B-lactamase sensitive resistant penicillins (e.g. nafcillin or cloxacillin), some cephalosporin or vancomycin OR
-> B-lactamase-sensitive penicillin (e.g. amoxicillin) + B-lactamase inhibitor (e.g. clavunic acid) combination
• 20% strain resistant to methicillin or naficillin by virtue penicllin-binding protein
-> Vancomycin +/- Gentamicin OR
-> Daptomycin OR
-> Trimethoprim-sulfamethoxazole or clindamycin
• Strain with intermediate resistance to Vancomycin (VISA) strains and with complete resistance to Vancomycin (VRSA) strain
-> Daptomycin OR Quinupristin-dalfopristin
11. 3. Treatment of toxic shock syndrome
• Correction of shock : Fluids, pressor drugs, inotropic drugs
• Administration of B-lactamase-resistant penicillin e.g. nafcillin
• Removal of tampon or debridement of infection site
• Pooled serum globulin, contains antibodies against TSST maybe useful
4. Skin infection
• Mupirocin- topical abx
13. Epidemiology
• S. epidermidis
- found on human skin, can enter blood stream at site of IV
catheterization
- Infection almost always hospital acquired
• S. saprophyticus
- found on mucosa of genital tract of young women, can ascend into
urinary bladder causing UTI
- Infection almost always community acquired
14. Virulence factor
• Strains of S.epidermidis produce glycocalyx more likely to adhere to
prosthetic implant materials
15. Clinical Features
S.Epidermidis
- Commonly infects IV catheters and prosthetic implants (e.g.
prosthetic heart valves [endocarditis], vascular grafts and prosthetic
joint s [arthritis or osteomyelitis])
- Major source of sepsis in neonates and of peritonitis in pt with renal
failure who undergone PD through indwelling catheter
- Most common bacteria causing CSF shunt infection
16. S. Saprophyticus
- Cause UTI esp in sexually active young women
- 2nd infection after E. coli causing community acquired UTI in young
women
S. Lugdunensis
- Cause prothetic valve endocarditis and skin infection
17. Laboratory Diagnosis
• Gram Stain: Fram-positive cocci in grapelike clusters
• Culture: nonhemolytic white colonies
• Reaction to Novobiocin: S.epidermidis – sensitive, S.saprophyticus-
resistant
• Catalase positive
• Coagulase negative
• Do not ferment mannitol
18. Treatment
• Highly antibiotic resistant
• Methicillin –sensitive strains (MSSE) – Produce B-lactamase but are
sensitive to B-lactamase resistant drugs e.g. nafcillin
• Methicillin/nafcillin-resistant (MRSE)
– Due to altered penicillin-binding proteins
- Vancomycin + rifampin/aminoglycoside
