2-5 questions please RESULTS AND INTERPRETATIONS-Lab Topic 9 Procedures 1-9 1. W

Question

2-5 questions please

RESULTS AND INTERPRETATIONS-Lab Topic 9 Procedures 1-9 1. Were your results as expected? If not, explairn hat test(s) is/are used in order to distinguish lactose fermenters from non-lactose fermenters? 3. Why are so many tests needed for the identification of the Enterobacteriaceae? 4. Why are selective and/or differential media so important for isolation and identification? 5. Why are these tests so important in the microbiology labi? 6. Where the results as expected? If not, explain. Literature Cited

Explanation / Answer

Answer:

2) Lactose fermenters are microorganisms which upon fermentation of lactose produce acid and gas as products.

Bacteria under the Enterobacteriaceae can be categorised as lactose and non-lactose fermenters. Examples of lactose fermenters being Escherichia coli, Klebsiella and non-lactose fermenters are salmonella and shigella.

Tests to distinguish between lactose and non- lactose fermenters.

Initially, lactose fermenting ability was based on fermentation on MacConkey's medium which is a differential medium that can distinguish lactose fermenters and non-fermenters on inoculation.

Lactose broth test: In this test, lactose broth containing beef extract, gelatin, peptone and lactose are used. Phenol red is the indicator.

A positive test shows a change from red/pink to yellow colour upon fermentation and reddish or no colour change points to non-lactose fermenters.

3) The family Enterobacteriaceae are the most most predominant bacteriae in our large intestines. The coliform bacteria are generally commensals in us although salmonella which is another member is known to cause enteric fever.

But within the family itself, they exhibit wide biochemical and antigenic heterogeneity. So hence there are various tests which can be helpful in clssifying and distinguishing them:

The indole, methyl red, Vogus-Proskauer, citrate utilization etc.

4)Selective and differential media such as MacConkey media is useful in differentiating lactose fermenters from non-lactose fermenters :

Result : an appearance of bright pink colonies due to lactose fermentation.

triple sugar iron agar(TSI) can distinguish sucrose, lactose and glucose fermenters from each other. Other media used are Eosin Methylene Blue(EMB) Agar; Ecoli gives a black precipitate on EMB.

Salmonella shigella agar(SS) agar.

The use of differential media gives a more confirmatory support on the identification as to which specific organism is causing the disease so that prompt treatment can be immediately initiated.

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