5&6 - Microbio 1&2 Flashcards
selection vs screen in culture
selection - select against things you don’t want to grow
screen - looking for a specific pathogen based on an indicator or something like that
MacConkey agar
selects for gram negs - differentiates lactose fermenters vs non fermenters via color change
colistin naladixic acid (CNA) plate
selects for gram pos organisms
H flu needs to be grown on
chocolate agar
sputum acceptability criteria
do direct gram stain
>10 squamous epithelial cells per lpf - not ok
<10 squamous cells/lpf and likely have multiple PMNs - good sample
growth indicator for blood cultures
CO2 production
most important factor influencing sensitivity of blood cultures
volume of blood drawn (20-30 ml per vial - one aerobe one anaerobe - ideal for adults)
length of routine blood culture incubation and how soon do pos ones usually turn pos?
5 d
most pos ones are pos by 2 d
how many cultures are needed to detect most non-endocarditis blood stream infections?
2-3 (pre-abx!!)
common blood culture contaminants
coagulase neg staph
bacillus sp
viridans group strep
corynebacteria
quantitative urine culture specimens
clean catch - use 0.001 ml (mult # cols by 1000 for CFU/ml)
catheter - use 0.01 ml (mult by 100)
criteria for reporting urine culture results
> 10^4 CFU/ml and <10^4 CFU/ml - descriptive only
any quantity of group B strep in infants or gonorrhea/chlamydia in adolescents/adults
difference between target amplification and signal amplification in molecular diagnostics
target amp - ex pcr, make copies of the target itself
signal amp - make copies of something that binds to target
problem w/ serology
could indicate recent, but no longer current, infection unless you have multiple time points to show it rising
