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MSK, rheum, derm > staph and strep > Flashcards

staph and strep Flashcards

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Dermatology Board Prep flashcards
1
Q

how do differentiate staph from other bacteria?

A

catalase positive

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2
Q

describe the hemolysis of the 3 staph

A

aureus: beta

epidermidis and saprophyticus: none

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3
Q

what bacteria ferments mannitol?

A

staph aureus

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4
Q

which bacteria have urease?

A

staph epidermidis and saprophyticus

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5
Q

how can you differentiate b/w staph epidermidis and saprophyticus on culture

A

epidermidis: novobiocin sensitive
saprophyticus: novobiocin resistant

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6
Q

how is coagulase positive shown in lab?

A

causes rabbit plasma to clot

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7
Q

what virulence factor of staph causes sudden onset of fever/chills and how?

A

peptidoglycan: stimualtes macros to produce cytokines, activates complement/coagulation cascades (like endotoxin)

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8
Q

what virulence factor is specific to MRSA and responsible for the severe skin/soft tissue infections and necrotizing PNA it causes?

A

PVL

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9
Q

what bacteria causes scalded skin syndrome? what toxin is responsible? how does it work?

A

staph aureus
exfoliatin/exfoliative toxins A and B
proteases that cleave desmoglein

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10
Q

what toxin is responsible for food poisoning by staph aureus? how does it work?

A

enterotoxin A

superantigen in GI tract: IL-1/2 release from macros, T cells

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11
Q

how is staph epi treated? why?

A

with vancomycin b/c infections caused by epi would only be due to MRSE

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12
Q

what’s the virulence factor for staph epi?

A

formation of biofilm

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13
Q

which strep hydrolize esculin in presence of bile?

A

GDS: enterococcus and strep. bovis

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14
Q

what is bacitracin used to differentiate b/w?

A

GAS: bacitracin sensitive
GBS: bacitracin resistant

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15
Q

which bacteria hydrolyzes hippurate?

A

GBS

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16
Q

how do you differentiate b/w the two species of GDS?

A

enterococcus: growth in hypertonic saline

strep. bovis: no growth in hypertonic saline

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17
Q

how do you differentiate b/w the alpha hemolytic species?

A

strep viridans: resistant to lysis by bile, optochin resistant
strep pneumo: lysis by bile, optochin sensitive

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18
Q

which species are alpha hemolytic? beta? gamma/non?

A

alpha: viridans and pneumo
beta: GAS, GBS, GCS, GGS (also staph aureus)
non: GDS (strep bovis and enterococcus)

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19
Q

antibodies to what antigen of GAS are tested for?

A

streptolysin O, not SLS b/c not antigenic

20
Q

what two virulence factors are responsible for the beta hemolysis of GAS?

A

Streptolysin O: oxygen labile so lower layers below surface of agar
SLS: oxygen stable so on surface of agar

21
Q

how can you clinically distinguish GAS pharyngitis from other causes?

A

GAS pharyngitis doesn’t show URT symptoms (cough, runny nose, etc)

22
Q

what is the difference between staph and strep impetigo

A

staph: bullous
strep: papules progress to pustules/vesicle and break down to form golden adherent crusts-also around mouth

23
Q

what two virulence factors are responsible for GAS necrotizing fasciitis? their action?

A

streptococcal trypsinlike protease: degrades IL-8, prevents PMN migration
pyrogenic exotoxin B: protease that degrades tissue

24
Q

what exotoxin is responsible for rash of scarlet fever? what bug?

A

GAS

erythrogenic toxin: acts as superantigen

25
Q

what exotoxin is responsible for strep TSS?

A

pyrogenic exotoxin A: superantigen

26
Q

what is characteristic of the rash of scarlet fever? what is another characteristic finding?

A

feels like sandpaper due to small papules

strawberry tongue

27
Q

describe the JONES criteria for diagnosing acute rheumatic fever

A

Joints: migratory polyarthritis
O: endocarditis
Nodules: subcutaneous, firm and painless
Erythema marginatum: evanescent, pink rash on trunk
Sydenham chorea: abrupt involuntary movements

28
Q

where is GBS found normally? what is the concern for CBS colonization and what is done in response?

A

colon, genital tract of women

neonatal infection from vertical transmission so screen all pregnant women at 35-37 weeks gestation

29
Q

what should be done if endocarditis is caused by GDS?

A

if it’s due to strep. bovis, look for colon cancer

30
Q

what bacteria is associated with infections following dental surgery or with poor dentition?

A

viridans group strep

-colonizes mouth and colon

31
Q

what’s the main cause of subacute endocarditis? what else does it cause?

A

viridans group strep

-abscesses in brain, liver, abdomen

32
Q

what bacteria is usually found in mixed/polymicrobial anaerobic infections/abscesses

A

poststreptococcus

33
Q

Dnase/streptodornase

A

GAS: degrades DNA, protecting from Neutrophil Extracellular Traps

34
Q

alpha toxin

A

staph aureus: hemolysin, forms holes in host cells, causes necrosis of skin and hemolysis

35
Q

Protein A

A

staph aureus: binds Fc portion of IgG and prevents complement activation, no C3b produced means phagocytosis reduced

36
Q

streptolysin O

A

GAS: cytotoxic, protects from phagocytic killing; oxygen labile hemolysin

37
Q

M toxin

A

GAS: anti-phagocytic, many types are reason for ability to cause multiple infections

38
Q

lipotechoic acid

A

staph aureus: induces IL-1 and TNF from macros

39
Q

coagulase

A

staph aureus: activates prothrombin to thrombin and fibrinogen to fibrin, serves to wall off infected site and delays migration of PMN’s by forming a clot

40
Q

streptokinase

A

GAS: activates plasminogen to plasmin, dissolves fibrin in clots

41
Q

Panton Valentine leukocidin

A

MRSA: pore-forming cytotoxin, causes leukocyte destruction and tissue necrosis

42
Q

teichoic acid

A

staph aureus: mediate adherence of staph to mucosal cells

43
Q

C5a peptidase

A

GAS: cleaves C5a, minimizes influx of PMNs in early infection

44
Q

staphyloxanthin (carotenoid)

A

staph aureus: inactivates superoxides and ROS within neutrophils, causes golden color of colonies on plates

45
Q

gamma toxin/leukotoxin

A

staph aureus: lyses phagocytes and RBCs

46
Q

hyaluronidase

A

GAS: spreading factor-important in spread of cellulitis, skin infections

47
Q

streptolysin S

A

GAS: cytotoxic, protects from phagocytic klling; oxygen stable hemolysin (weaker effects than SLO)

MSK, rheum, derm (6 decks)

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