Staph Aureus Flashcards
Staph Aureus
what % of people are colonized with s. aureus in their nose?
30%
Staph Aureus
what is folliculitis?
infected pilosebaceous unit; can also affect apocrine glands and causes sycosis barbae in facial hair
Staph Aureus
what is a furuncle?
folliculitis culminating in a deep nodule extending SQ (boil)
Staph Aureus
carbuncle
coalescing of neighboring furuncles
Staph Aureus
how do you treat folliculitis?
moist heat & drainage, can use antibiotics if there is surrounding cellulitis or it is on face (Clindamycin, TMP/SMX)
Staph Aureus
non-bolus impetigo
small, superficial, intraepidermal vesiculopustules that readily rupture, releasing honey-like golden crust; caused by GAS/S. aureus mixture; treat with oral erythromycin, mupirocin
Staph Aureus
bolus impetigo
intraepidermal vesicles that are flaccid bullae filled with yellow “pus”
Staph Aureus
Nikolsky’s sign
means that vesicle will go away/subside with pressure
Staph Aureus
what causes bolus impetigo?
S. aureus, phage group II with ETA or ETB serine protease toxins
Staph Aureus
how to treat bolus impetigo?
topical mupirocin, clindamycin, TMS, linezolid
Staph Aureus
staphylococcal scalded skin syndrome (SSSS)
Pemphigus neonatorum caused by ETA/ETB positive phage group II S. aureus; results from sepsis leading to systemic exposure to ETA/ETB
Staph Aureus
how to treat SSSS?
IV vancomycin
Staph Aureus
how do exfoliating toxins A and B work?
target Desmoglein-1 in desmosomal cadherins, leads to sloughing of squamous corneal layer in epidermis, muscle where desmosomes endure mechanical stress
Staph Aureus
what % of staph. aureus strains have exfoliating toxins?
~10%
Staph Aureus
erysipelas vs. cellulitis
ery: superficial, orange appearance; cellulitis: deeper, more painful
Staph Aureus
s. aureus food poisoning (enterotoxins)
caused by emetic superantigen toxin (SEA-SEU) that is heat stable, competes with salmonella for most common source of food poisoning in US
Staph Aureus
what is the course/rx for s. aureus food poisoning?
lasts 4-8 hours, no treatment
Staph Aureus
toxic shock syndrome
TSST-1 is a superantigen toxin that leads to T cell overactivation
Staph Aureus
s. aureus bacteremia
mortality as high as 50%; bacteria must have capsule, resistence, survival within neutrophils in order to survive in blood
Staph Aureus
infective endocarditis
10-40% of bacteremia cases progress to infective endocarditis, where one or more heart valves, walls, or septae are colonized by oral streptococci (secondary to prior damage) or staph. Aureus (can be spontaneous)
Staph Aureus
prosthetic valve endocarditis is caused by what organism?
staph epidermidis
Staph Aureus
staph aureus pneumonia frequently occurs secondary to what infection, and has what mortality rate?
bacterial superinfection post-influenza with about 50% mortality
Staph Aureus
patients with what genetic disorder are at especially high risk of staph aureus pneumonia?
Cystic Fibrosis: develop small colony variants (SVCs) from spontaneous mutation of chronic staph aureus colonization in their lungs (due to intense antiobiotic therapy that selects for resistant strains)
Staph Aureus
what are SVCs?
slow growing, non-pigmented, non-hemolytic staph aureus mutants that are difficult to detect and resistant to several antiobiotics
Staph Aureus
Osteomyelitis infects what bones in children? How about adults?
long bones in children, vertebrae in adults
Staph Aureus
why is osteomyelitis so difficult to treat?
persists inside osteoblasts; difficult to get antibiotics there
Staph Aureus
staph aureus is the most common cause of what joint disorder in children?
septic arthritis
Staph Aureus
what is the most common cause of septic arthritis in adults?
gonococcus (neisseria gonorrhea)
Staph Aureus
infective endocarditis is more serious and more difficult to treat when it is on what side of the heart?
left-sided (mitral valve): more oxygenated and so more bacteria
Staph Aureus
right-sided infective endocarditis is usually caused by what?
IV drug use (tricuspid valve)
Staph Aureus
staph aureus pneumonia is mostly associated with what strains?
PVL-positive
Staph Aureus
name three important characteristics of staph aureus hemolysin toxins?
1) pore-forming lytic toxins that kill blood cells, 2) avoid phagocytosis by separating biofilms from neutrophils, 3) nutrient release
Staph Aureus
what is one feature of the surface of staph aureus that prevents phagocytosis?
binds Ig in wrong direction so that Fc is hidden from host immune receptors
Staph Aureus
why is septic staph aureus 90% lethal pre-antibiotics?
it has developed mechanisms to evade all forms of innate immune response
Staph Aureus
what is sortase?
transpeptidase that attaches surface proteins to cell wall; play role in adhesion, virulence, infection, colonization
Staph Aureus
how is the staph aureus genome organized?
core structure + pathogenicity islands with resistance, virulence, etc on mobile elements
Staph Aureus
what is the most famous pathogenicity island on staph aureus?
mecA, came from chickens, provides beta-lactam resistance
Staph Aureus
what particular MRSA strain is now being found in both hospital and community acquired infections?
USA300
Staph Aureus
what type of test should be done to determine if a patient has inducible resistance to clindamycin (a lincosamide)?
D Test
Staph Aureus
which nephrotoxic drug is particularly effective in treating MRSA?
vancomycin
