u A brief introduction to IMViC tests: The IMViC tests are a group of individual tests used in microbiology lab testing to identify an organism in the coliform group. A coliform is a gram negative, aerobic or facultative aerobic rod which produces gas from lactose within 48 hours. The presence of some coliforms indicate fecal contamination. The IMViC Tests Enterics are Gram-negative bacteria that grow in the intestinal tract of humans and other animals. The IMViC tests is used to identify these microbes such as Klebsiella, Enterobacter, and Escherichia coli. IMViC tests is used to differentiate these three organisms. IMViC is an acronym that stands for indole , methyl red, Voges-Proskauer , and citrate . To obtain the results of these four tests, three test tubes are inoculated: tryptone broth (indole test), methyl red - Voges Proskauer broth (MR-VP broth), and citrate. The Indole Test Test organism is inoculated into tryptone broth, a rich source of the amino acid tryptophan. Indole positive bacteria such as Escherichia coli produce tryptophanase, which cleaves tryptophan, producing indole and other products. Kovac's reagent is then added to the broth. Postive results: Dark pink colour develops. *The indole test must be read by 48 hours of incubation The Methyl Red and Voges-Proskauer Tests The methyl red (MR) and Voges-Proskauer (VP) tests are read from a single inoculated tube of MR-VP broth. After 24-48 hours of incubation the MR-VP broth is split into two tubes. One tube is used for the MR test and the other for the VP test. MR-VP media contains glucose and peptone. All enterics oxidize glucose for energy, however the end products vary depending on bacterial enzymes. Methyl red is then added to the broth. Bacteria that produce acid causes pH to drop below 4.4. Positive MR Results: Broth turns cherry red Bacteria which cannot grow in neutral pH breaks down the peptone, causing the pH to rise above 6.2. Negative MR Results: Broth is yellow in colour. Reagents used for the VP test are alpha-napthol and potassium hydroxide. These reagents are added the broth. Positive VP Results: Reagents turn a pink-burgundy color (Acetyl methyl carbinol is present). *This may take 20 to 30 minutes to develop The Citrate Test The citrate test is used to determine if a bacterium can grow utilizing citrate as its sole carbon and energy source.Simmon's citrate media contains bromthymol blue, a pH indicator. -Yellow at acidic pH's (around 6) -Blue at more alkaline pH's (around 7.6) Simmon's citrate agar has an intermediate green color. Positive Results: Agar turns blue Enterobacter and Klebsiella are citrate positive while E.coli is negative. [posted by chocobo237 at 6:51 AM][website]

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