staph and strep Flashcards
how do differentiate staph from other bacteria?
catalase positive
describe the hemolysis of the 3 staph
aureus: beta
epidermidis and saprophyticus: none
what bacteria ferments mannitol?
staph aureus
which bacteria have urease?
staph epidermidis and saprophyticus
how can you differentiate b/w staph epidermidis and saprophyticus on culture
epidermidis: novobiocin sensitive
saprophyticus: novobiocin resistant
how is coagulase positive shown in lab?
causes rabbit plasma to clot
what virulence factor of staph causes sudden onset of fever/chills and how?
peptidoglycan: stimualtes macros to produce cytokines, activates complement/coagulation cascades (like endotoxin)
what virulence factor is specific to MRSA and responsible for the severe skin/soft tissue infections and necrotizing PNA it causes?
PVL
what bacteria causes scalded skin syndrome? what toxin is responsible? how does it work?
staph aureus
exfoliatin/exfoliative toxins A and B
proteases that cleave desmoglein
what toxin is responsible for food poisoning by staph aureus? how does it work?
enterotoxin A
superantigen in GI tract: IL-1/2 release from macros, T cells
how is staph epi treated? why?
with vancomycin b/c infections caused by epi would only be due to MRSE
what’s the virulence factor for staph epi?
formation of biofilm
which strep hydrolize esculin in presence of bile?
GDS: enterococcus and strep. bovis
what is bacitracin used to differentiate b/w?
GAS: bacitracin sensitive
GBS: bacitracin resistant
which bacteria hydrolyzes hippurate?
GBS
how do you differentiate b/w the two species of GDS?
enterococcus: growth in hypertonic saline
strep. bovis: no growth in hypertonic saline
how do you differentiate b/w the alpha hemolytic species?
strep viridans: resistant to lysis by bile, optochin resistant
strep pneumo: lysis by bile, optochin sensitive
which species are alpha hemolytic? beta? gamma/non?
alpha: viridans and pneumo
beta: GAS, GBS, GCS, GGS (also staph aureus)
non: GDS (strep bovis and enterococcus)
antibodies to what antigen of GAS are tested for?
streptolysin O, not SLS b/c not antigenic
what two virulence factors are responsible for the beta hemolysis of GAS?
Streptolysin O: oxygen labile so lower layers below surface of agar
SLS: oxygen stable so on surface of agar
how can you clinically distinguish GAS pharyngitis from other causes?
GAS pharyngitis doesn’t show URT symptoms (cough, runny nose, etc)
what is the difference between staph and strep impetigo
staph: bullous
strep: papules progress to pustules/vesicle and break down to form golden adherent crusts-also around mouth
what two virulence factors are responsible for GAS necrotizing fasciitis? their action?
streptococcal trypsinlike protease: degrades IL-8, prevents PMN migration
pyrogenic exotoxin B: protease that degrades tissue
what exotoxin is responsible for rash of scarlet fever? what bug?
GAS
erythrogenic toxin: acts as superantigen
what exotoxin is responsible for strep TSS?
pyrogenic exotoxin A: superantigen
what is characteristic of the rash of scarlet fever? what is another characteristic finding?
feels like sandpaper due to small papules
strawberry tongue
describe the JONES criteria for diagnosing acute rheumatic fever
Joints: migratory polyarthritis
O: endocarditis
Nodules: subcutaneous, firm and painless
Erythema marginatum: evanescent, pink rash on trunk
Sydenham chorea: abrupt involuntary movements
where is GBS found normally? what is the concern for CBS colonization and what is done in response?
colon, genital tract of women
neonatal infection from vertical transmission so screen all pregnant women at 35-37 weeks gestation
what should be done if endocarditis is caused by GDS?
if it’s due to strep. bovis, look for colon cancer
what bacteria is associated with infections following dental surgery or with poor dentition?
viridans group strep
-colonizes mouth and colon
what’s the main cause of subacute endocarditis? what else does it cause?
viridans group strep
-abscesses in brain, liver, abdomen
what bacteria is usually found in mixed/polymicrobial anaerobic infections/abscesses
poststreptococcus
Dnase/streptodornase
GAS: degrades DNA, protecting from Neutrophil Extracellular Traps
alpha toxin
staph aureus: hemolysin, forms holes in host cells, causes necrosis of skin and hemolysis
Protein A
staph aureus: binds Fc portion of IgG and prevents complement activation, no C3b produced means phagocytosis reduced
streptolysin O
GAS: cytotoxic, protects from phagocytic killing; oxygen labile hemolysin
M toxin
GAS: anti-phagocytic, many types are reason for ability to cause multiple infections
lipotechoic acid
staph aureus: induces IL-1 and TNF from macros
coagulase
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
streptokinase
GAS: activates plasminogen to plasmin, dissolves fibrin in clots
Panton Valentine leukocidin
MRSA: pore-forming cytotoxin, causes leukocyte destruction and tissue necrosis
teichoic acid
staph aureus: mediate adherence of staph to mucosal cells
C5a peptidase
GAS: cleaves C5a, minimizes influx of PMNs in early infection
staphyloxanthin (carotenoid)
staph aureus: inactivates superoxides and ROS within neutrophils, causes golden color of colonies on plates
gamma toxin/leukotoxin
staph aureus: lyses phagocytes and RBCs
hyaluronidase
GAS: spreading factor-important in spread of cellulitis, skin infections
streptolysin S
GAS: cytotoxic, protects from phagocytic klling; oxygen stable hemolysin (weaker effects than SLO)
