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{{Short description|Microbiological and biochemical method for identification}}
{{More footnotes needed|date=January 2015}}
{{One source|date=January 2015}}

The '''IMViC''' tests are a group of individual tests used in microbiology lab testing to identify an organism in the [[Coliform bacteria|coliform group]]. A coliform is a [[Gram-negative bacteria|gram negative]], aerobic, or [[facultative anaerobic organism|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#Methyl red test|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]].

[[File:IMViC Results.jpg|thumb|IMViC Results]]

== Indole test ==
{{Main|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&nbsp;°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 ==
{{Main|Methyl red|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 test|methyl red (MR) test]] and one for the [[Voges–Proskauer test|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 ==
{{Main|Citrate test}}
In the 1930's, S.A. Koser conducted experiments that were used to study bacterial catabolism of organic acids.<ref>{{Cite web |last=MacWilliams |first=Maria P. |date=December 8, 2009 |title=Citrate test Protocol |url=https://asm.org/ASM/media/Protocol-Images/Citrate-Test-Protocol.pdf?ext=.pdf |access-date=April 16, 2023 |website=American Society for Microbiology}}</ref> Koser found that citrate metabolism could be an indicator for bacteria found in natural environments. Additionally, citrate could be used to distinguish bacterial coliforms 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.<ref>{{Cite web |last=Tankeshwar |first=Acharya |date=2013-05-17 |title=Citrate Utilization Test: Principle, Procedure, Results • Microbe Online |url=https://microbeonline.com/citrate-utilization-test/ |access-date=2023-04-16 |website=Microbe Online |language=en-us}}</ref> 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 ==

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.<ref>{{Cite book|last1=Ananthanarayan|first1=R|title=Ananthanarayan and Paniker's Textbook of Microbiology|last2=Jayaram Paniker|first2=CK|publisher=[[Orient Longman]]|year=2005|isbn=8125028080|location=[[Chennai]], [[India]]}}</ref>

{|class="wikitable" border="1"
!width="100"| Species
!width="100"| Indole
!width="100"| Methyl Red
!width="100"| Voges-Proskauer
!width="100"| Citrate
|-
| ''[[Escherichia coli]]''
| style="background:#98FB98" align="center"| Positive
| style="background:#98FB98" align="center"| Positive
| style="background:#ffa07a" align="center"| Negative
| style="background:#ffa07a" align="center"| Negative
|-
| ''[[Staphylococcus aureus]]''
| style="background:#ffa07a" align="center"| Negative
| style="background:#98FB98" align="center"| Positive
| style="background:#98FB98" align="center"| Positive
| style="background:#ffa07a" align="center"| Negative
|-
| ''[[Shigella]] spp.'' <ref>[http://www.microbiologyinpictures.com/shigella.html Microbiology in pictures]</ref>
| style="background:#ffa07a" align="center"| Negative
| style="background:#98FB98" align="center"| Positive
| style="background:#ffa07a" align="center"| Negative
| style="background:#ffa07a" align="center"| Negative
|-
| ''[[Salmonella]] spp.''
| style="background:#ffa07a" align="center"| Negative
| style="background:#98FB98" align="center"| Positive
| style="background:#ffa07a" align="center"| Negative
| style="background:#98FB98" align="center"| Positive
|-
| ''[[Klebsiella]] spp.''
| style="background:#ffa07a" align="center"| Negative
| style="background:#ffa07a" align="center"| Negative
| style="background:#98FB98" align="center"| Positive
| style="background:#98FB98" align="center"| Positive
|-
| ''[[Proteus vulgaris]]'' <ref>Microbe Library {{cite web |url=http://www.microbelibrary.org/library/2-associated-figure-resource/2553-imvic-tests-of-proteus-vulgaris |title=IMViC tests of Proteus vulgaris - Library |access-date=2013-01-05 |url-status=dead |archive-url=https://web.archive.org/web/20130119011528/http://www.microbelibrary.org/library/2-associated-figure-resource/2553-imvic-tests-of-proteus-vulgaris |archive-date=2013-01-19 }}</ref>
| style="background:#98FB98" align="center"| Positive
| style="background:#98FB98" align="center"| Positive
| style="background:#ffa07a" align="center"| Negative
| style="background:#ffa07a" align="center"| Negative
|-
| ''[[Proteus mirabilis]]''
| style="background:#ffa07a" align="center"| Negative
| style="background:#98FB98" align="center"| Positive
| style="background:#ffa07a" align="center"| Negative
| style="background:#98FB98" align="center"| Positive
|-
| ''[[Citrobacter freundii]]''
| style="background:#ffa07a" align="center"| Negative
| style="background:#98FB98" align="center"| Positive
| style="background:#ffa07a" align="center"| Negative
| style="background:#98FB98" align="center"| Positive
|-
| ''[[Enterobacter aerogenes]]''
| style="background:#ffa07a" align="center"| Negative
| style="background:#ffa07a" align="center"| Negative
| style="background:#98FB98" align="center"| Positive
| style="background:#98FB98" align="center"| Positive
|}

==References==
<references />
{{Clinical microbiology techniques}}

[[Category:Microbiology]]