You are given a mixed culture of 3 bacteria - Methicillin- resistant Staphylococ

Question

You are given a mixed culture of 3 bacteria - Methicillin- resistant Staphylococcus aureus (MRSA), Escherichia coli and Enterobacter aerogenes. Assume that Escherichia coli can ferment glucose, maltose, sucrose and lactose and also produce carbon dioxide gas on fermenting these. Assume that Enterobacter aerogenes can ferment only sucrose and cannot ferment glucose, maltose and lactose fermenting sucrose it produces hydrogen sulphide g ferment any of these 4 sugars but forms endospores and is sensitive to penicilin. Also they all give similar looking white-colored colonies on an agar plate. Also on as. Assume that MRSA does not Question: Generate pure cultures of these 3 bacteria using the following tools that you learned in the lab. Use any (some or all) of these tools to generate pure cultures as well as confirm them. A) Any of Staining methods B) Special media plates (McConkey Agar or Blood Agar or Mannitol Agar plates) C) Fermentation media tubes (Triple Sugar Iron (TSI) or Durham tubes) D) Any of the disc diffusion test Assume for your answers the use of Agar plates or burners or boiling water bath allowed and any reagent can be supplied. Points included for correctly writing the names of bacteria using the rules of nomenclature

Explanation / Answer

Answer:

when using the 3 different strains Staphylococcus aureus, Escherichia coli, Enterobacter aerogenes. the following tests give subsequent reactions:

A) Staining methods: staining methods will reveal some differentiation among this three groups

Staphylococcus aureus - Gram positive cocci

Escherichia coli - Gram negative cocci

Enterobacter aerogenes - Gram negative cocci

here we can differentiate S.aureus with this test.

B) Special media plates: selective media can be used to differentiate these bacteria.

but as per the principle of this confirmation tests, the bacteria should capable of utilising the sugar/ sustrate provided in the medium. (eexample: S.aureus will produce yellow colonies on mannitol salt agar plates. but it has to ferment mannitol in this case)

C) Fermentation media tubes: This is the right way for differentiating these bacteria. because fermentation methods are clearly mentioned in the above statement. so by inoculating the selective strains into the medium, we can differentiate the bacteria.

D) Disk diffusion test: Entero bacteriace is generally oxidase negative. so by using this method we can differentiate E.coli.

conclusion:

First use gram staing method to differentiate the gram positive cocci form the remaining colonies. aftert that using a selective medium, we can differtiate the enterobacter species from the other. finally with sugar fermentation test, we can confirm the pure cultures.

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