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Staph Aureus Flashcards

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2
Q

Staph Aureus

what % of people are colonized with s. aureus in their nose?

A

30%

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3
Q

Staph Aureus

what is folliculitis?

A

infected pilosebaceous unit; can also affect apocrine glands and causes sycosis barbae in facial hair

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4
Q

Staph Aureus

what is a furuncle?

A

folliculitis culminating in a deep nodule extending SQ (boil)

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5
Q

Staph Aureus

carbuncle

A

coalescing of neighboring furuncles

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6
Q

Staph Aureus

how do you treat folliculitis?

A

moist heat & drainage, can use antibiotics if there is surrounding cellulitis or it is on face (Clindamycin, TMP/SMX)

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7
Q

Staph Aureus

non-bolus impetigo

A

small, superficial, intraepidermal vesiculopustules that readily rupture, releasing honey-like golden crust; caused by GAS/S. aureus mixture; treat with oral erythromycin, mupirocin

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8
Q

Staph Aureus

bolus impetigo

A

intraepidermal vesicles that are flaccid bullae filled with yellow “pus”

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9
Q

Staph Aureus

Nikolsky’s sign

A

means that vesicle will go away/subside with pressure

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10
Q

Staph Aureus

what causes bolus impetigo?

A

S. aureus, phage group II with ETA or ETB serine protease toxins

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11
Q

Staph Aureus

how to treat bolus impetigo?

A

topical mupirocin, clindamycin, TMS, linezolid

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12
Q

Staph Aureus

staphylococcal scalded skin syndrome (SSSS)

A

Pemphigus neonatorum caused by ETA/ETB positive phage group II S. aureus; results from sepsis leading to systemic exposure to ETA/ETB

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13
Q

Staph Aureus

how to treat SSSS?

A

IV vancomycin

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14
Q

Staph Aureus

how do exfoliating toxins A and B work?

A

target Desmoglein-1 in desmosomal cadherins, leads to sloughing of squamous corneal layer in epidermis, muscle where desmosomes endure mechanical stress

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15
Q

Staph Aureus

what % of staph. aureus strains have exfoliating toxins?

A

~10%

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16
Q

Staph Aureus

erysipelas vs. cellulitis

A

ery: superficial, orange appearance; cellulitis: deeper, more painful

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17
Q

Staph Aureus

s. aureus food poisoning (enterotoxins)

A

caused by emetic superantigen toxin (SEA-SEU) that is heat stable, competes with salmonella for most common source of food poisoning in US

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18
Q

Staph Aureus

what is the course/rx for s. aureus food poisoning?

A

lasts 4-8 hours, no treatment

19
Q

Staph Aureus

toxic shock syndrome

A

TSST-1 is a superantigen toxin that leads to T cell overactivation

20
Q

Staph Aureus

s. aureus bacteremia

A

mortality as high as 50%; bacteria must have capsule, resistence, survival within neutrophils in order to survive in blood

21
Q

Staph Aureus

infective endocarditis

A

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)

22
Q

Staph Aureus

prosthetic valve endocarditis is caused by what organism?

A

staph epidermidis

23
Q

Staph Aureus

staph aureus pneumonia frequently occurs secondary to what infection, and has what mortality rate?

A

bacterial superinfection post-influenza with about 50% mortality

24
Q

Staph Aureus

patients with what genetic disorder are at especially high risk of staph aureus pneumonia?

A

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)

25
Q

Staph Aureus

what are SVCs?

A

slow growing, non-pigmented, non-hemolytic staph aureus mutants that are difficult to detect and resistant to several antiobiotics

26
Q

Staph Aureus

Osteomyelitis infects what bones in children? How about adults?

A

long bones in children, vertebrae in adults

27
Q

Staph Aureus

why is osteomyelitis so difficult to treat?

A

persists inside osteoblasts; difficult to get antibiotics there

28
Q

Staph Aureus

staph aureus is the most common cause of what joint disorder in children?

A

septic arthritis

29
Q

Staph Aureus

what is the most common cause of septic arthritis in adults?

A

gonococcus (neisseria gonorrhea)

30
Q

Staph Aureus

infective endocarditis is more serious and more difficult to treat when it is on what side of the heart?

A

left-sided (mitral valve): more oxygenated and so more bacteria

31
Q

Staph Aureus

right-sided infective endocarditis is usually caused by what?

A

IV drug use (tricuspid valve)

32
Q

Staph Aureus

staph aureus pneumonia is mostly associated with what strains?

A

PVL-positive

33
Q

Staph Aureus

name three important characteristics of staph aureus hemolysin toxins?

A

1) pore-forming lytic toxins that kill blood cells, 2) avoid phagocytosis by separating biofilms from neutrophils, 3) nutrient release

34
Q

Staph Aureus

what is one feature of the surface of staph aureus that prevents phagocytosis?

A

binds Ig in wrong direction so that Fc is hidden from host immune receptors

35
Q

Staph Aureus

why is septic staph aureus 90% lethal pre-antibiotics?

A

it has developed mechanisms to evade all forms of innate immune response

36
Q

Staph Aureus

what is sortase?

A

transpeptidase that attaches surface proteins to cell wall; play role in adhesion, virulence, infection, colonization

37
Q

Staph Aureus

how is the staph aureus genome organized?

A

core structure + pathogenicity islands with resistance, virulence, etc on mobile elements

38
Q

Staph Aureus

what is the most famous pathogenicity island on staph aureus?

A

mecA, came from chickens, provides beta-lactam resistance

39
Q

Staph Aureus

what particular MRSA strain is now being found in both hospital and community acquired infections?

A

USA300

40
Q

Staph Aureus

what type of test should be done to determine if a patient has inducible resistance to clindamycin (a lincosamide)?

A

D Test

41
Q

Staph Aureus

which nephrotoxic drug is particularly effective in treating MRSA?

A

vancomycin

Host Defense & Microbiology (19 decks)

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