Exercise 22 IMViC Tests Flashcards
used to separate what
coliforms
define coliforms
gram -ive, facultative anaerobic, non endospore forming, rod shaped bacteria that produce acid and gas from lactose within 48 hours at 37 C
indole test tests for
ability to produce trytophanase. hydrolyzes the aa tryptophn into indole, pyruvic acid and ammonia
what medium is used for indole test and reagent
1% tryptone in water, indole reagent, an acid solution of para-dimethylaminobenzaldehyde in alcohol
what is a positive rxn of indole
reagent combines with indole to form a red layer that floats on the surface of medium
what is a negative rxn of indole
no red colour
how to avoid false -ve of indole test and why it occurs
some bacteria degrade indole itself. trpytonr culture tets no more than 4 days after incubation
most significant ingredient of MR-VP is
dextrose
mixed acid fermentation leads to production of
fermentation acids
butanediol fermentation forms
butanediol, actoin, and fewer organic acids. pH does not fall
methyl red changes when and what colours
red below pH of 4.4, yellow at 6 and above
why is it important to incubate for at least 48 hours for MR-VP tests
false positive if still undergoing butanediol fermentation. tube will appear red
VP test identifies
bacteria that ferment glucose through butanediol fermentation leading to an accumulation of 2,3-butanediol
how is 2,3-butanediol tested
VP reagent easily detects acetoin, a precursor of 2,3-butanediol
what are the VP reagents
VP reagent A id alphanaphthol and VP reagent B is 40% KOH
what is a positive test for VP
reagents and acetoin will produce a cherry red colour at the air-broth interface unless shaken to supply sufficient oxygen
what does MR-VP positive for both mean
species has enzyme systems for both mixed acid fermentation and butanediol fermentation. medium is very acidic but also has acetoin accumulation
simmons citrate agar contains
mineral salts, only carbon source is citrate and sole nitrogen is ammonium ions, brom thymol blue pH
brom thymol blue changes when
green is neutral, abouve 7,6 is blue
simmon citrate agar tests for
bacteria able to transport citrate into the cell and use ammonium ions instead of aa as nitrogen soure
implication of simmons citrate
all coliforms metabolize citrate when generated inside cell. not all can bring citrate acrss cytoplamic membrane unless have transport enzyme called citrate permeases
growth but no colour change on simmons citrate agar is this postive
yes, to avoid confusion between growth and heavy inoculum, transfer with a needle
