Staphylococci

Question 1

properties and mechanism of Staphylococcus aureus

Answer 1

• gram +
• beta hemolytic
• catalase +
• coagulase +
• cocci in clusters
• protein A (virulence factor) binds Fc-IgG–inhibits complement activation and phagocytosis
• commonly colonizes the nares

Question 2

what does Staphylococcus aureus cause?

Answer 2

• inflammatory disease
• toxin mediated disease
• MRSA (methicillin resistant S. aureus)

Question 3

Inflammatory disease

Answer 3

• caused by S. aureus
• causes:
  
  • skin infections
  • organ abcesses
  • pneumonia–often after influenza virus infection
  • endocarditis
  • septic arthritis
  • osteomyelitis

Question 4

Toxin mediated disease

Answer 4

• caused by S. aureus
• causes:
  
  • toxic shock syndrome (TSST-1)
  • scalded skin syndrome–exfoliatic toxin
  • rapid onset food poisoning–enterotoxins

Question 5

MRSA

Answer 5

• caused by S. aureus
• important cause of serious nosocomial and community acquired infections
• resistant to methicillin and nafcillin b/c of altered penicillin binding protein

Question 6

TSST-1 toxin

Answer 6

• superantigen that binds to MHC II and T cell receptor resulting in polyclonal T cell activation

Question 7

how does staphylococcal toxic shock syndrome (TSS) present? what is it associated with?

Answer 7

• presentation:
  
  • fever
  • vomiting
  • rash
  • desquamation
  • shock
  • end organ failure
  • inc AST
  • inc ALT
  • inc bilirubin
• associated with prolonged use of vaginal tampons or nasal packing

Question 8

Staphyloccal TSS vs. Streptococcus pyogenes TSS

Answer 8

• Streptococcal TSS is a toxic shock life syndrome associated with painful skin infection

Question 9

S. aureus food poisoning

Answer 9

• due to ingestion of preformed toxin –> short incubation period (2-6 hours) followed by nonbloody diarrhea and emesis
• enterotoxin is heat stable –> not destroyed by cooking

Question 10

Staphylococcus–catalase, coagulase, abscess

Answer 10

• catalase +
  
  • “Staph make catalase b/c they have more ‘staff’”
• coagulase +
  
  • bad staph (aureus) make coagulase and toxins
• forms fibrin clot around self –> abscess

Question 11

properties of Staphylococcus epidermidis

Answer 11

• gram +
• catalase +
• coagulase -
• urease + cocci in clusters
• novobiocin sensitive

Question 12

Staphylococcus epidermidis:

where is it normal? where does it contaminate?

what does it infect?

Answer 12

• normal flora of skin
• contaminates blood cultures
• infects by producing adherent biofilms
  
  • prosthetic devices–hip implant, heart valve
  • IV catheters

Question 13

properties of Staphylococcus saprophyticus

Answer 13

• gram +
• catalase +
• coagulase -
• urease + cocci in clusters
• novobiocin resistant

Question 14

Staphylococcus saprophyticus

where is it normal?

what kind of infection does it often cause?

Answer 14

• normal flora of female genital tract and perineum
• second most common cause of uncomplicated UTI in young women
  
  • most common cause is E. coli