#bacterial identification

Demonstration of Carbohydrate metabolism (oxidation and fermentation of glucose) by microorganisms by Hugh-Leifson’s test

The microorganisms such as fungi, bacteria, actinomycetes, etc. Utilize carbohydrate as a source of carbon and energy through catabolism (enzymatic breakdown) and show growth and biomass production. However, utilization of carbohydrate is carried out aerobically (using molecular oxygen as electron acceptor for oxidation) and anaerobically (using inorganic ions, other than molecular oxygen as…

Catalase activity test for bacterial identification

Most of aerobes and facultative anaerobes have the characteristic of showing catalase activity. Actually, these organisms utilize oxygen to produce hydrogen peroxide. The hydrogen peroxide is toxic to their enzyme system. Hence, these organisms produce an enzyme catalase, which converts the hydrogen peroxide to water and oxygen. It is also that the reason of not surviving anaerobes in the…

Citric acid (citrate) utilization by bacteria: Requirement, Procedure and Result

This test is used for differentiation of E. coli with Enterobacter aerogenes. It is a widely acceptable test for testing the presence of E. coli, a fecal organism in water which cannot utilize citrate as carbon source while E. aerogenes can use it. Secondly, citric acid is an intermediate of metabolic product of Kreb’s cycle which oxidizes pyruvate to CO2. The bacterium must have an ability to…

Methyl Red (MR) and Voges-Proskauer (VP) test: Principle, Requirement and Result

The enteric bacteria fall under two groups (the mixed acid fermenters and 2,3-butanediol) as far as fermentation of glucose and production of products are concerned. The mixed fermenters produce large amount of acids and the butanediol fermenters produces the neutral end products called acetoin (acetyl methyl carbinol). Since both the tests are preformed simultaneously and on the same medium (MR…

Indole production from tryptophan test: principle, procedure and result

There are some enteric bacteria that produce indole during the hydrolysis of tryptophan. Not all bacteria hydrolyze tryptophan through the production of tryptophanase. However, there are few bacteria that do not produce indole. Indole production can be detected using Kuvac’s reagent that gives cherry-red a layer of reagent. 

So, indole production can be considered as characteristic property of…

When a broth culture is inoculated with a small bacterial inoculum, the population size of the bacteria increases showing a classical pattern. The bacterial growth curve shows the following four distinct phases. 

1. Lag phase:

Bacterial Growth Curve

After a liquid culture broth is inoculated, the multiplication of bacteria does not start immediately. It takes some time to multiply or to adjust in…