Wednesday, 18 February 2015

HOW TO IDENTIFY BACTERIA


About Test For Bacteria

Staining Reactions:

 Staining is a simple basic technique that is used to identify microorganisms. Simple staining is used to study the morphology of all microorganisms (Fig 1).
The simple stain uses the basic dyes such as Methylene blue or basic fuschin. The strong negative charge of the bacterial cell will strongly bind with the positive charged basic dyes and will impart its colour to all bacteria.
 Gram staining is a differential staining technique that imparts different colours to different bacteria or bacterial structures. Usually it differentiates bacteria into two groups; gram positive and gram negative. The primary stain Crystal violet and mordent Iodine form a strong CVI complex all bacteria. Gram positive cells due to their thick peptidoglycan layer will retain the CVI complex even after it is subjected to decolourization with acetone or alcohol. Hence the counter stain Safranin has no action on gram positive cells. But in the case of gram negative, the thin peptidoglycan layer and more lipid contents in the cell wall will easily make them susceptible to the action of decolorizer and hence CVI complex is easily washed out and hence the gram negative cells will the colour of counter stain Safranin.  Hence after the gram staining, the gram positive cells appear as purple and gram negative cells appear as pink (Fig 2). The study of morphological features  and staining characteristics help in the preliminary identification of the isolate.

Biochemical reactions:


About Test For Bacteria
Gram negative enteric bacilli play an important role in the contamination of food. Hence they are the main causative agents of intestinal infection. Gram negative family includes Shigella, Salmonella, Proteus, Klebsiella,Escherichia,Enterobacter etc. Usually four tests are used for differentiation of the various members of Enterobactericeae. They are Indole test,Methyl red test, Voges proskauer test and Citrate test; collectively known as IMViC series of reactions.


 Indole test:

Indole tests looks for the presence or absence of tryptophanase enzyme production of the bacteria. If the enzyme is present, it will degrade the aminoacid tryptophan in the media and will produce Indole, ammonia and pyruvic acid. Indole will react with Kovac's reagent to produce a cherry red complex, which indicates a positive indole test. The absence of red color is indicative of tryptophan hydrolysis due to the lack of tryptophanse enzyme.

Methyl Red Test

This test detects the ability of microorganism to ferment glucose and to produce acidic end products. Enteric organism produces pyruvic acid from glucose metabolism. Some enteric will then use the mixed acid pathway to metabolize pyruvic acid to other acidic products such as lactic acid, acetic acid and formic acids. This will reduce the pH of the media. Methyl red is a pH indicator which is red at the acidic pH (below 4.4) and yellow at alkaline pH (above 7). The formation of red color after the addition of Methyl red reagent indicates the accumulation of acidic end products in the medium and is an indicative of positive test

No comments:

Post a Comment

I HOPE THIS HAVE BEEN VERY INFORMATIVE,

Get the Full Material delivered to your Email, . Call us on 07034538881

Follow Us On Twitter,
Like Us On Facebook,
Join Our Cycle On Google+

we can keep u updated by subscribing for free using your email
For more clarification, Please Leave a comment.

Related Posts Plugin for WordPress, Blogger...