microbiology lab days 5 and 6 part 2 (biochemical assay, fermentation, beta galactosidase, onpg, TSI
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what is tsi agar used to detect?
presence of sugar fermentation, gas production and H2S production.
what does saccharolytic mean?
the term saccharolytic can be used to describe those microorganisms that are capable of breaking the glycosidic bonds within carbohydrates
how do you interpret the results of the TSI agar test?
Red butt/slant indicates alkalinity, yellow butt/slant indicates acidity, black deposits indicate presence of H2S, bubble at the bottom indicates gas production
what is the aim of the IMViC test?
to identify enteric bacteria
what are the four parts of the IMViC test?
indole test, methyl red test, Voges-proskauer test, citrate test
bacteria produce enzyme tryptophanase to hydrolyse an amino acid called tryptophan to a metabolic product called _____
indole reacts with _____ _____ to give a color change
what does a positive indole test look like?
formation of red color layer on top
what is the principle of the methyl red test?
some microorganisms produce mixed acids which reduces pH to below 4 to cause a color change to red color (+ve test). other organisms produce less acids, not enough to produce color change, so appear yellow.
voges proskauer test detects which chemical?
During the voges proskauer test, which reagent is added to the medium?
barritt's reagent that contains 40% KOH and 5% α-naphthol
how do you interpret the results of a Voges proskauer test?
+VP test: red color development within 15 min of addition of reagent
-VP test: no color change
what agar is used in the citrate test?
simmons citrate agar slant containing sodium citrate, ammonia, and bromothymol blue
Citrate utilization in the citrate test causes the pH of the medium to ____ because...
pH increases because there is a buildup of alkaline product formation, which causes a color change.
how do you interpret the results of the citrate test?