Standard Plate Counts and IMViC Tests for Bacterial Contamination in Minced Chicken

This article discusses the use of standard plate counts and IMViC tests to identify bacterial contamination in minced chicken. The article also covers the results of the tests and their interpretation.

Running head: MICROBIOLOGY
Topic: MICROBIOLOGY
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Discussion
Standard plate counts are methods for quantification of bacteria though the calculation
of colony forming units (CFU) which gives an estimate of the number of cells through skilled
interpretation of the number of CFUs (Davis, 2014). Standard plate count was conducted to
calculate the number of plates present per gram of meat (Ahmad et al., 2013). From the
results of the standard plate counts performed on abused as well as fresh minced chicken, it
has been found that for all the serial dilutions from 10-1 to 10-4, more than 300 colonies have
been found showing increased chances of high infection rates. To identify the presence
of coliform group and gram negative contamination in the abused minced chicken sample,
IMViC tests were conducted (Chishimba et al., 2016).
ImViC tests have been performed on the abused chicken samples only. According to
Gomez Aldapa et al (2016), after counting of most probable number (MPN), ImViC tests are
used for the biochemical and generic characterisation of E.coli along with AP-20 tests. Indole
test was conducted where two samples were kept in the broth of peptone water containing
tryptophan. Enzyme tryptophanase react with tryptophan to produce pyruvate, ammonium
and indole molecule. Kovac’s reagent is added to Indole. Presence of the red layer is a
positive sign for the test. Red layer is seen on the top of liquid in case of abused minced
chicken and hence Indole test have been positive for the sample.
MRVP broth is used in methyl red test which detects acid production using pyruvate.
Methyl Red is used as a pH indicator. Red colour appeared in abused minced chicken and
gave positive result for bacterial contamination. MRVP broth is also used in Voges-Proskauer
test. Alpha-naphthol and potassium hydroxide is used to identify the presence of
acetylmethylcarbinol. Negative result was reflected in abused chicken as pinkish red colour
was not seen. Simmon's citrate agar is used in citrate test. Agar contains ammonium ions,

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citrate and Bromothymol blue. After the abused chicken was added, the citrate agar became
blue thus confirming citrate test for the abused sample. The change in colour from green to
blue is a sign of positive result and thus, the citrate test have been positive for E.coli. From
the Imvic profile it has been found that E.coli has given Indole methyl red and Citrate tests
positive results. However the VP test have been negative.

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References
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