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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 anaerobic rod, which produces gas from lactose within 48 hours. The presence of some coliforms indicate fecal contamination.
The term "IMViC" is an acronym for each of these tests. "I" is for indole test; "M" is for methyl red test; "V" is for Voges-Proskauer test, and "C" is for citrate test. The lower case "i" is merely for "in" as the Citrate test requires coliform samples to be placed "in Citrate".
In this test, the organism under consideration is grown in peptone water broth. It contains tryptophan, which under the action of enzyme tryptophanase is converted to an Indole molecule, pyruvate and ammonium. The indole is then extracted from the broth by means of xylene. The broth is sterilized for 15 minutes at around 121°C. To test the broth for indole production, Kovac's reagent . Kovac's reagent consist of amyl alcohol and para-dimethylaminobenzaldehyde and concentrated hydrochloric acid. Kovac's reagent is actually used to determine ability of an organism to separate indole from amino acid tryptophan and it is added after incubation. A positive result is indicated by a pink/red layer forming on top of the liquid.
These tests both use the same broth for bacterial growth. The broth is called MR-VP broth. After growth, the broth is separated into two different tubes, one for the methyl red (MR) test and one for the Voges-Proskauer (VP) test.
The methyl red test detects production of acids formed during metabolism using mixed acid fermentation pathway using pyruvate as a substrate. The pH indicator Methyl Red is added to one tube and a red color appears at pH's lower than 4.2, indicating a positive test (mixed acid fermentation is used). The solution remaining yellow (pH = 6.2 or above) indicates a negative test, meaning the butanediol fermentation is used.
The VP test uses alpha-naphthol and potassium hydroxide to test for the presence of acetylmethylcarbinol (acetoin), an intermediate of the 2,3-butanediol fermentation pathway. After adding both reagents, the tube is shaken vigorously then allowed to sit for 5–10 minutes. A pinkish-red color indicates a positive test, meaning the 2,3-butanediol fermentation pathway is used.
In the 1930's, S.A. Koser conducted experiments that were used to study bacterial catabolism of organic acids.[1] Koser found that citrate metabolism could be an indicator for bacteria found in natural environments. Additionally, citrate could be used to distinguish bacterial coilforms found in soil, and aquatic environments, such as Enterobacteiacea , and coilforms with fecal contamination. It was found that coilforms without fecal contamination grew, while the coilforms with fecal contamination did not grow.
This test uses Simmon's citrate agar to determine the ability of a microorganism to use citrate as its sole carbon and energy source. The agar contains citrate and ammonium ions (nitrogen source) and bromothymol blue (BTB) as a pH indicator.[2] Bromothymol blue was added in order to reduce false positives. The citrate agar is green before inoculation, and turns blue, because of BTB as a positive test indicator, meaning citrate is utilized. The test is also prepared on a slant to maximize bacterial growth for an even better indication of the use of citrate.
Usageedit
These IMViC tests are useful for differentiating the family Enterobacteriaceae, especially when used alongside the Urease test.
The IMViC results of some important species are shown below.[3]
^Microbe Library . Archived from the original on 2013-01-19. Retrieved 2013-01-05.
April 11, 2024
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This article includes a list of general references but it lacks sufficient corresponding inline citations Please help to improve this article by introducing more precise citations January 2015 Learn how and when to remove this template message This article relies largely or entirely on a single source Relevant discussion may be found on the talk page Please help improve this article by introducing citations to additional sources Find sources IMViC news newspapers books scholar JSTOR January 2015 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 anaerobic rod which produces gas from lactose within 48 hours The presence of some coliforms indicate fecal contamination The term IMViC is an acronym for each of these tests I is for indole test M is for methyl red test V is for Voges Proskauer test and C is for citrate test The lower case i is merely for in as the Citrate test requires coliform samples to be placed in Citrate These tests are useful in distinguishing members of Enterobacteriaceae IMViC ResultsContents 1 Indole test 2 Methyl red and Voges Proskauer test 3 Citrate test 4 Usage 5 ReferencesIndole test editMain article Indole test In this test the organism under consideration is grown in peptone water broth It contains tryptophan which under the action of enzyme tryptophanase is converted to an Indole molecule pyruvate and ammonium The indole is then extracted from the broth by means of xylene The broth is sterilized for 15 minutes at around 121 C To test the broth for indole production Kovac s reagent Kovac s reagent consist of amyl alcohol and para dimethylaminobenzaldehyde and concentrated hydrochloric acid Kovac s reagent is actually used to determine ability of an organism to separate indole from amino acid tryptophan and it is added after incubation A positive result is indicated by a pink red layer forming on top of the liquid Methyl red and Voges Proskauer test editMain articles Methyl red and Voges Proskauer test These tests both use the same broth for bacterial growth The broth is called MR VP broth After growth the broth is separated into two different tubes one for the methyl red MR test and one for the Voges Proskauer VP test The methyl red test detects production of acids formed during metabolism using mixed acid fermentation pathway using pyruvate as a substrate The pH indicator Methyl Red is added to one tube and a red color appears at pH s lower than 4 2 indicating a positive test mixed acid fermentation is used The solution remaining yellow pH 6 2 or above indicates a negative test meaning the butanediol fermentation is used The VP test uses alpha naphthol and potassium hydroxide to test for the presence of acetylmethylcarbinol acetoin an intermediate of the 2 3 butanediol fermentation pathway After adding both reagents the tube is shaken vigorously then allowed to sit for 5 10 minutes A pinkish red color indicates a positive test meaning the 2 3 butanediol fermentation pathway is used Citrate test editMain article Citrate test In the 1930 s S A Koser conducted experiments that were used to study bacterial catabolism of organic acids 1 Koser found that citrate metabolism could be an indicator for bacteria found in natural environments Additionally citrate could be used to distinguish bacterial coilforms found in soil and aquatic environments such as Enterobacteiacea and coilforms with fecal contamination It was found that coilforms without fecal contamination grew while the coilforms with fecal contamination did not grow This test uses Simmon s citrate agar to determine the ability of a microorganism to use citrate as its sole carbon and energy source The agar contains citrate and ammonium ions nitrogen source and bromothymol blue BTB as a pH indicator 2 Bromothymol blue was added in order to reduce false positives The citrate agar is green before inoculation and turns blue because of BTB as a positive test indicator meaning citrate is utilized The test is also prepared on a slant to maximize bacterial growth for an even better indication of the use of citrate Usage editThese IMViC tests are useful for differentiating the family Enterobacteriaceae especially when used alongside the Urease test The IMViC results of some important species are shown below 3 Species Indole Methyl Red Voges Proskauer CitrateEscherichia coli Positive Positive Negative NegativeStaphylococcus aureus Negative Positive Positive NegativeShigella spp 4 Negative Positive Negative NegativeSalmonella spp Negative Positive Negative PositiveKlebsiella spp Negative Negative Positive PositiveProteus vulgaris 5 Positive Positive Negative NegativeProteus mirabilis Negative Positive Negative PositiveCitrobacter freundii Negative Positive Negative PositiveEnterobacter aerogenes Negative Negative Positive PositiveReferences edit MacWilliams Maria P December 8 2009 Citrate test Protocol PDF American Society for Microbiology Retrieved April 16 2023 Tankeshwar Acharya 2013 05 17 Citrate Utilization Test Principle Procedure Results Microbe Online Microbe Online Retrieved 2023 04 16 Ananthanarayan R Jayaram Paniker CK 2005 Ananthanarayan and Paniker s Textbook of Microbiology Chennai India Orient Longman ISBN 8125028080 Microbiology in pictures Microbe Library IMViC tests of Proteus vulgaris Library Archived from the original on 2013 01 19 Retrieved 2013 01 05 Retrieved from https en wikipedia org w index php title IMViC amp oldid 1199502192, wikipedia, wiki, book, books, library,
