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HDID 2 > 35. Staphylococci > Flashcards

35. Staphylococci Flashcards

1
Q

staphylococci, streptococci, & enterococci - catalase+/-?

A

catalase +: staphylococci

catalase -: streptococci & enterococci

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2
Q

staphylococci & O2?

A

facultative anaerobes

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3
Q

most virulent strains of staphylococci have a _____ which inhibits phagocytosis

A

polysaccharide capsule

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4
Q

many staphylococci have an outer _____ that facilitates the adherence of the bacteria to surfaces like catheters, shunts, and implants.

A

slime layer

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5
Q

staphylococcal orgs - coagulase + or -?

A

S. aureus = coagulase +

S. epidermidis, S. saphrophyticus, & S. lygdenensis = coagulase -

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6
Q

color of S. aureus and S. epidermidis on blood culture?

A

S. aureus = gold/yellow

S. epidermidis = white

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7
Q

the virulence of S. aureus depends on what abilities (4)?

A

evade host immune response

adhere to host tissues

destroy host tissue

evade abx tx

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8
Q

how does S. aureus evade the host immune response?

A
  1. capsule (helps inhibit phagocytosis by compromising neutrophil access)
  2. Protein A = cell wall protein w/multiple Fc IgG receptors - so binds IgG in an incorrect orientation so that the neutrophil doesn’t recognize it and thus inhibits phagocytosis
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9
Q

how does S. aureus adhere to host?

A

surface adhesions:

many adhesion proteins = MSCRAMM (includes protein A, also fibrinogen, fibronectin, elastin, and collagen) to facilitate adherence to host

Protein A binds to vWF (adhesion re: endothelial damage)

binds to host proteins

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10
Q

how does S. aureus destroy host tissues?

A

ENZYMATIC

promotes bacterial spread/invasion through tissues (coagulase & microthrombus formation to dist to other tissues, hyaluronidase & hydrol of hyaluronic acid to get through cartilage)

improves bacterial survival (catalase removes H2O2)

tissue destruction (fibrinolysin & dissolves fibrin clots; lipases & hydrol of lipids; nucleases & hydrol of DNA)

TOXIN:

cytotoxins (hemolysins and leukocidin like PV lyse cell membranes & destroy leukocytes, erythrocytes, and macrophages)

cytolytic peptides (recruit then lyse neutrophils, overproduced in CA-MRSA )

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11
Q

S. aureus and PCN resistance?`

A

95% resistance thanks to penicillinases

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12
Q

PV leukocidin?

A

cytotoxin that causes leukocyte destruction and tissue necrosis. It is present in many strains (marker for particularly virulent strains) of CA-S.aureus (esp S/ST and PNA)

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13
Q

which staphylococci toxins are always produced?

A

hemolysins and leukocidin

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14
Q

which staphylococci toxins are associated w/specific syndromes?

A

exfoliative toxins = scalded skin syndrome

enterotoxin = food poisoning

toxic shock syndrome toxin I = sepsis

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15
Q

S. aureus and methicillin resistance?

A

50% thanks to MecA gene making new PBP = PBP2A.

so resistant to all semi-synthetic pcns: nafcillin (IV) and dicloxacillin (oral)

confers resistance to other B-lactam agents

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16
Q

S.aureus and vancomycin resistance?

A

rare: 1%

encoded by vanA gene (VRE)

alteration of binding site (so no longer D-ala-D-ala but D-ala-D-lac)

all pts colonized w/BOTH VRSA and MRSA (so many vanA gene is shared)

VISA still common but still rare-> thickened cell wall resulting in inability of abx to penetrate (excess D-ala-D-ala soaks up all of the vancomycin)

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17
Q

what % of people are colonized w/ S. aureus?

A

30%

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18
Q

pyogenic infections caused by S. aureus?

A

cutaneous: impetigo, folliculitis, furuncles, carbuncles, wound infections
systemic: pna, empyema, osteomyelitis, septic arthritis, endocarditis, bacteremia

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19
Q

toxin-mediated clinical syndromes caused by S. aureus?

A

scalded skin syndrome, food poisoning, toxic shock syndrome

20
Q

impretigo re: S. aureus?

A

children

contagious

infection of superficial skin layer (small flattened red macule, into pus-filled vescicle/pustule w/erythrematous base, to ruptures w/ YELLOW CRUSTING)

21
Q

S. aureus & folliculitis?

A

pyogenic infection of hair follicles - raised painful lesion on indurated base

stye if at base of eyelid

22
Q

furuncles and carbuncles & S. aureus?

A

furuncle = boil

  • extension of folliculitis
  • large, painful, pus-filled nodules

carbuncle
- coalesce involving multiple hair follicles and spread into deeper subQ tissues

23
Q

S. aureus and wound infectoins?

A

after trauma/surgery (can be small)

possible foreign body: splinter, suture, implant

greater morbidity than other cutaneous pyogenic infections

24
Q

the likelihood that S.aureus bacteremia will progress to pna, osteomyelitis, septic arthritis, or endocarditis increases w/what?

A

duration of infection

25
Q

HA-S.aureus occur as a result of what?

A

Rx (surgery, intervention, device, etc)

26
Q

CA-S.aureus occurs in what type of people?

A

those without other medical conditions

27
Q

clinical disease of CA-S.aureus?

A

furuncles, pna (rare)

28
Q

clinical disease of HA-S.aureus?

A

device associated or surgical site infections

29
Q

staphylococcal scalded skin syndrome?

A

toxinosis: infection usu in umbilical cord and the organism produces toxin which disseminates in the bloodstream

young children w/no Abs

epidermolytic toxins (exfoliative) - lysis of desmosomes in epidermal granular cell layer

cutaenous blisters w/no organisms or inflammatory cell s(toxin only)

no scarring

self-limiting

30
Q

bullous impetigo?

A

localized scalded skin syndrome

local spread of toxin around a colonized/infected wound in ppl w/ some immunity against the toxin

localized blistering occurs w/bacteria and inflammatory cell filled blisters (due to close proximity of infection/colonization)

31
Q

staphylococcal food poisoning?

A

acute onset, w/in 2-6 hours

N/V, diarrhea, and abd pain w/o fever

ingestion of pre-formed toxin

enterotoxins (SEA): heat and acid stable, superantigens (increase peristalsis, fluid loss, N/V/D), interacts w/vagal emetic receptors

treatment is supportive (IV fluids)

32
Q

staphylococcal toxic shock syndrome

A

acute onset

fever, hypotension

progression to sepsis/shock

diffuse erythematous rash (often desquamates)

***TSST-1 is MOST COMMON

tx of infection necessary - w/appropriate abx and CONTROL THE SOURCE

33
Q

cagulase negative staphylococci - virulence factors?

A

slime layer

many of the same enzymes as S.aureus (catalase, hyaluronidase, penicillinase) but no (few) toxins

antimicrobial resistance common

34
Q

S. epidermidis infection?

A

infections of prosthetic material (cental vascular catheters, prosthetic joint/heart valve, vascular or CNS shunts)…thnx to SLIME LAYER

35
Q

S. saprophyticus infections?

A

young women UTIs leads to pyelonephritis sometimes

36
Q

S. lygdenensis infections?

A

native valve endocarditis (virulent like S.aureus)

37
Q

diagnosis of S. aureus infection?

A

clinical syndrome and culture evidence from sterile site or other site of inflammation (blood, skin site like abscess wound)

38
Q

diagnosis of coagulase-negative Staphylococci infection?

A

clinical syndrome and culture evidence:

from blood requires multiple positive cultures to rule out skin contamination

from sterile site (like prosthetic material) - still need multiple positives

39
Q

empiric therapy for a systemic staphylococcal infection?

A

vancomycin (or daptomycin if NOT PNEUMONIA)

40
Q

empiric therapy for a localized staphylococcal infection?

A

clindamycin, TMP/SMX, doxycycline, linezolid

41
Q

first line definitive therapy for serious staphylococcal infection?

A

anti-staphylococcal PCNs (nafcilin or cefazolin)

42
Q

2nd line definitive therapy for serious staphylococcal infection?

A

vancomycin or daptomycin (if NOT PNA)

43
Q

1st line definitive tx for outpatient staphylococcal infection?

A

anti-staphylococcal PCNs (dicloxacillin, cephalexin)

44
Q

2nd line definitive tx for outpatient staphylococcal infection?

A

clindamycin, TMP/SMX, doxycycline (CA-MRSA), or linezolid

but *** TMP/SMX and doxycycline may not cover streptococcus (the other common cause of S/ST infections)

45
Q

S.aureus vs Strep skin infections?

A

S.aureus: abscess, cellulitis w/purulence, Rx as if MRSA

Strep: raised, upper dermis; clear demarcations; intensely red

HDID 2 (32 decks)

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