Question

Selective and Differential media used in the laboratory: • Define selective media and use a particular medium as the example to explain how it works – Lecture 2 – slides 13, 14 and notes • Define differential media and use a particular medium as the example to explain how it works

Answer 1

A selective media is the one which is used for the growth and isolation of a specific (selected) group of microbes. A selective media allows the growth of certain type of bacteria whereas prevents the growth of some other type of bacteria. For example, eosin methylene blue is a selective media used for the growth of Gram Negative bacteria. The dyes present in this media act against the growth of Gram Positive Bacteria. Mannitol salt Agar is the media used for the growth of Gram Positive Bacteria.

A differential media is the one which is used to differentiate between closely related species of bacteria. For example, macconkey Agar is used for the differentiation of lactose fermenting bacteria. Blood Agar is used for the differentiation of various hemolytic bacteria on the basis of their ability to lyse red blood cells differently.

Some media like you seen methylene blue are both selective and differential. It selects Gram Negative bacteria out of Gram positive bacteria. And it is differential in the sense that it differentiates between various coliform bacteria.

Please rate.