Chapter 20, Problem 2VI

Summary Introduction

To describe:

The Gram reaction and lactose fermentation of the two different types of bacteria shown in the MacConkey agar plate.

Introduction:

MacConkey agar plate is the growth medium that is both selective in nature and is also differential. It facilitates the growth of Gram-negative bacteria, that is., E. Coli, in the dark pink portion of the plate; and it stops the growth of Gram-positive bacteria, that is., Salmonella enterica, which is identified by the yellow region on the plate. The E. Coli strain takes up its pink color after fermenting lactose, whereas, the other bacteria that does not ferment lactose remain unchanged, which in this case is S. enterica, present in the yellow region of the shown plate.