Isolation of Pure Cultures

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. Also on fermenting sucrose it produces hydrogen sulphide gas. Assume that MRSA does not ferment any of these 4 sugars but forms endospores and is sensitive to penicillin. Also they all give similar looking white-colored colonies on an agar plate.

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

Sample Solution