Biochemical Tests For Escherichia coli (E. coli) | Bacteriology Notes

BIOCHEMICAL TESTS FOR ESCHERICHIA COLI (E.COLI)

In this Article, we’re gonna discuss so many biochemical reactions for the well known causative agent of UTI (Urinary Tract Infections), Diarrhea & Pyogenic Infections i.e. the Escherichia coli abbreviated as E. coli, but a few reactions are most commonly used and are medically important for distinguishing pathogenic strains of E. coli from other non- pathogenic strains as well as from other species of Escherichia which are as follows:



Indole Positive

Methyl red Positive

Citrate Negative

Urease Negative

Voges – Proskauer Negative

LF colonies on MacConkey agar medium

Unable to produce H2S

Check out the Biochemical tests for Streptococcus pneumoniae

Besides that of various biochemical reactions and Sugar fermentation tests, certain enzymatic reactions are also medically important to distinguish Escherichia coli from other Escherichia sp.

IMViC test for Escherichia coli - biochemical test for e coli - imvic for e coli
A.) Indole: Positive B.) Methyl-Red: Positive C.) Voges-Proskauer test: Negative D.) Citrate test: Negative Image Source: ASM MicrobeLibrary

Below is the list of these Enzymatic Reactions and various other biochemical tests for  Escherichia coli which have great importance in research and for knowledge but are not routinely employed:

TESTSRESULTS
Acetate Utilization+VE (POSITIVE)
Alkaline Phosphatase+VE (POSITIVE)
Indole+VE (POSITIVE)
Methyl Red+VE (POSITIVE)
Nitrate Reduction+VE (POSITIVE)
ONPG+VE (POSITIVE)
Catalase-VE (NEGATIVE)
Citrate-VE (NEGATIVE)
Coagulase-VE (NEGATIVE)
DNase-VE (NEGATIVE)
Oxidase-VE (NEGATIVE)
Urease-VE (NEGATIVE)
VP (Voges Proskauer)-VE (NEGATIVE)
Arginine DehydrolaseVARIABLE (As per the Strain)




Escherichia coli and other species of Escherichia ferment various sugars producing acid with gas.

But these sugar fermentation tests are of no diagnostic value in routine laboratory tests except sucrose fermentation test, However, that is also not well understood and some strains are able to ferment sucrose as well, but it can be used in differentiating Escherichia coli, from other Pathogenic & non-pathogenic Escherichia species and Coliform bacteria.

The other sugar fermentation tests which are described below are of great importance in research work.

SUGARSRESULTS
Arabinose+VE (POSITIVE)
Dextrose+VE (POSITIVE)
Fructose+VE (POSITIVE)
Galactose+VE (POSITIVE)
Glucose+VE (POSITIVE)
Lactose+VE (POSITIVE)
Maltose+VE (POSITIVE)
Mannitol+VE (POSITIVE)
Mannose+VE (POSITIVE)
Melibiose+VE (POSITIVE)
Rhamnose+VE (POSITIVE)
Sorbitol+VE (POSITIVE)
Xylose+VE (POSITIVE)
Adonitol-VE (NEGATIVE)
Dulcitol-VE (NEGATIVE)
Cellobiose-VE (NEGATIVE)
Raffinose-VE (NEGATIVE)
Salicin-VE (NEGATIVE)
Sucrose-VE (NEGATIVE)
TrehaloseVARIABLE (depends on strain)

That’s all about the Biochemical tests for Escherichia coli




Further Reading:
Differentiation of Escherichia coli from coliforms Merck

IMViC Tests: Principle, Procedure, and results Microbeonline

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