Exercise 22 IMViC Tests

Question 1

used to separate what

Answer 1

coliforms

Question 2

define coliforms

Answer 2

gram -ive, facultative anaerobic, non endospore forming, rod shaped bacteria that produce acid and gas from lactose within 48 hours at 37 C

Question 3

indole test tests for

Answer 3

ability to produce trytophanase. hydrolyzes the aa tryptophn into indole, pyruvic acid and ammonia

Question 4

what medium is used for indole test and reagent

Answer 4

1% tryptone in water, indole reagent, an acid solution of para-dimethylaminobenzaldehyde in alcohol

Question 5

what is a positive rxn of indole

Answer 5

reagent combines with indole to form a red layer that floats on the surface of medium

Question 6

what is a negative rxn of indole

Answer 6

no red colour

Question 7

how to avoid false -ve of indole test and why it occurs

Answer 7

some bacteria degrade indole itself. trpytonr culture tets no more than 4 days after incubation

Question 8

most significant ingredient of MR-VP is

Answer 8

dextrose

Question 9

mixed acid fermentation leads to production of

Answer 9

fermentation acids

Question 10

butanediol fermentation forms

Answer 10

butanediol, actoin, and fewer organic acids. pH does not fall

Question 11

methyl red changes when and what colours

Answer 11

red below pH of 4.4, yellow at 6 and above

Question 12

why is it important to incubate for at least 48 hours for MR-VP tests

Answer 12

false positive if still undergoing butanediol fermentation. tube will appear red

Question 13

VP test identifies

Answer 13

bacteria that ferment glucose through butanediol fermentation leading to an accumulation of 2,3-butanediol

Question 14

how is 2,3-butanediol tested

Answer 14

VP reagent easily detects acetoin, a precursor of 2,3-butanediol

Question 15

what are the VP reagents

Answer 15

VP reagent A id alphanaphthol and VP reagent B is 40% KOH

Question 16

what is a positive test for VP

Answer 16

reagents and acetoin will produce a cherry red colour at the air-broth interface unless shaken to supply sufficient oxygen

Question 17

what does MR-VP positive for both mean

Answer 17

species has enzyme systems for both mixed acid fermentation and butanediol fermentation. medium is very acidic but also has acetoin accumulation

Question 18

simmons citrate agar contains

Answer 18

mineral salts, only carbon source is citrate and sole nitrogen is ammonium ions, brom thymol blue pH

Question 19

brom thymol blue changes when

Answer 19

green is neutral, abouve 7,6 is blue

Question 20

simmon citrate agar tests for

Answer 20

bacteria able to transport citrate into the cell and use ammonium ions instead of aa as nitrogen soure

Question 21

implication of simmons citrate

Answer 21

all coliforms metabolize citrate when generated inside cell. not all can bring citrate acrss cytoplamic membrane unless have transport enzyme called citrate permeases

Question 22

growth but no colour change on simmons citrate agar is this postive

Answer 22

yes, to avoid confusion between growth and heavy inoculum, transfer with a needle