Staph

Question 1

Characteristics:

Answer 1

• gram positive
• aerobic
• catalase positive
• nonmotile and facultative anaerobes
• highly variable among strains
• adaptive immunity ineffective so recurrent infection is common

**NO VACCINE

Question 2

Differentiating:

Answer 2

-coagulase test:

coagulase positive = s. aureus

negative = epidermidis

Question 3

Virulence factors:

Answer 3

• capsule
• protein A (spa)
• alpha toxin: exotoxin forms pores that causes water to rush in = tissue damage
• beta toxin: damages membrane
• exfolitative toxin: proteases that cleave cell-cell contact (cause EXFOLIATION)
• enterotoxin: food poisoning, function as superantigens to activate cytokine release
• TSS toxin: superantigen
• enzymes that help penetrate tissue/spread

Question 4

Protein A:

Answer 4

• expressed only by Aureus
• binds to Fc region of antibodies and prevents binding to antigens
• immune evasion

Question 5

S. Aureus:

Answer 5

• much more virulent than coagulase negative staph
• often leads to abscess formation
• often detected on the nares and places that you touch
• 20% of individuals are persistent carriers, some are intermediate or non-carriers

Question 6

S. epidermidis:

Answer 6

-on everyones skin

Question 7

S. Aureus epidemiology:

Answer 7

• successfully expand genetically related clones

- drives increased rate of methicillan resistant MRSA strains (currently USA 3000)

Question 8

Diseases caused by S. Aureus:

Answer 8

• Staph Scalded skin syndrome: young children, skin falls off, no scarring low mortality
• impetigo: localized form of scalded skin called bullous impetigo, infants with blisters
• pyogenic (pus forming): IF YOU SEE PUS THINK STAPH
• folliculitis: infection of hair follicle, called a stye if on eye
• carbuncles: furuncles (boils) coalesce, more systemic infection
• bacteremia/endocarditis: heart valve
• pneumonia/empyma: pus between lung and chest wall
• osteomyelitis/septic arthritis
• food poisoning: not from infection but ingestion of the enterotoxin (so even if you cook it right it wont go away)
• TSS

Question 9

TSS:

Answer 9

• localized growth of aureus
• produces TSS toxin in blood
• hypotension, diffuse macular rase (symptoms are rapid onset)
• must treat immediately

“sunburn” rash

Question 10

Coagulase negative staph diseases:

Answer 10

• endocarditis: of artificial heart valves
• catheter and shunt infections
• prosthetic joint infection
• UTI
• foreign body infection

Question 11

Staph treatment:

Answer 11

• resistance huge problem
• almost all strains resistant to penicillan due to penicillinases
• menthicillins used but also resistance by altered penicillin binding protein introduced by a phage, now resistant to all beta lactam antibiotics
• most MRSA multidrug resistant
• vancomycin remains effective when given through IV (using this drives resistance in other microbes such are VR resistant enterococcus)
• different patterns of resistance in community acquired and hospital acquired
• MRSA isolates encode altered penicillin binding proteins