Staphylococci

Question 1

staphylococci characteristics

Answer 1

gram +, clusters

single cell membrane, thick cell wall

non-motile, non-sporeforming, facultative anaerobe

polysac capsule differs among strains

catalase positive

Question 2

Staph aureus

Answer 2

catalase +

coagulase + (prothrombin to thrombin–>fibrinogen to fibrin–>clot)

beta-hemo, golden colonies

Question 3

normal flora of staph aureus

Answer 3

anterior nares; also vaginal, perirectal, inguinal areas

enter by beaks in skin, trauma, insect bites, catheters, etc

Question 4

What does this picture show?

Answer 4

pyrogenic disease–> cellulitis of skin with our without absecess (point to area of least resistance)

Question 5

What are other pyrogenic skin manifistation?

Answer 5

impetigo, folliculitis, furuncle, carbuncle

Question 6

Enterotoxin

Answer 6

pre-formed by bacteria in food before ingestion–>food poisoning

Question 7

TSST-1 produced locally (eg. cellulitis or vaginal tampon)–>blood systemic effects

Question 8

If staph aureus becomes bacteremic what can it cause?

Answer 8

endocarditis, osteomyelitis

Question 9

What is the mechanism of suprantigens?

Answer 9

cross link T cells R and class II MHC molecules–> stimulate T cells non specifically–> release of pro-inflammatory cytokines (TNFa)–>shock

Question 10

What caused this?

Answer 10

toxic shcok syndrome- may occurs with localized infection such as cellulities or with vaginal tampon or post surgical packing

manifistations- fever, erythema of the skin, followed by desquamation, conjuctivitis, strawberry, delirium, and shock

Question 11

What bacteria causes this?

Answer 11

staph aureus–>scalded-skin syndrome

infants/young children

fever and generalize desquamation with large bullae

exfoliant, a protease, caues separation of layers in the spidermins

Question 12

virulance factors: adhesion to host cells and substances:

Answer 12

teichoic acids- polymers of ribitol phosphate and lalow bacterial to stick to mucosal cells

lipoteochoic acid- pro-inflammatory

Question 13

virulance factors: enzymes

Answer 13

coagulase- clots that walls off abscss from leukocytes

staphylokinase- plasminogen activator, lyses fibrin, allow spread of infection

Question 14

virulance factor: PV-leucocidin-

Answer 14

post forming tocin that damages WBC, associated w/ severe skin/soft tissue infect and MRSA

Question 15

virulance factor: avoidance of host responses

Answer 15

proteins A binds to Fc fragment of IgG at site that complement binds, thereby preventing activation of complement

Question 16

virulance factors: carb capsule

Answer 16

poorly immunogenic

Question 17

Treatment for suppurative infections?

Answer 17

incision and surgical drainage may be enough, AB alone not enough

Question 18

tx for TSS- remove foreign body or drain the suppuration. support BP and cardiac fxn

Question 19

Diagnosis for s. aureus

Answer 19

gram stain smears show gram + cocci in clusters, but absence does not rule out!

in TSS- profound systemic effects, but blood cultures are often negative

no antigen, toxin, or ab test

Question 20

What does a positive blood culture for S. epidermidis tell us?

Answer 20

may be from contamination at phlebotomy site

Question 21

s. epidermidis characteristics

Answer 21

coagulase -

novobiocin sensitive

infect acquire through hospital or invasive med procedure, catheters, artificial heat valves, foreign body, etc.

lack toxins and invasion enzymes, no TSS

Question 22

Biofilms

Answer 22

bacteria attached to foregn body express exopolysaccharide

will help bacteria avoid immune defenses (eg. phagocytosis)

Biofilms also occur w/ S. aureus

Question 23

antibiotic resistance

Answer 23

penicillin–>methicillin/nafcillin/cephalosporins–>vancomysin–>daptomycin/quinupristin-daldopristin

Question 24

MRSA

Answer 24

90% strains have plasmid that encode a beta-actamase enzyme–>thus penicillin resistant

>50% of hospital strains and increased number of community acquired strains carry transferable mecA genes that encode altered penicillin-binding proteins–>met resistant (also to nafcillin, oxacillin, and cephalosporins

• may be resistance to fluroqinolones, and topical muprocin
• vanco resistant too, but less frequent.