MACCONKEY BROTH (PURPLE) (CM5a) 500g - Oxoid CM0505

MACCONKEY BROTH (PURPLE)
Code: CM0505
Description
MacConkey Broth has long been used as a presumptive medium for the detection of the coli-aerogenes organisms. In the original medium, litmus was employed as the indicator of acid production but, in later publications, MacConkey suggested neutral red as a more satisfactory alternative. Childs & Allen1 showed that some samples of neutral red exerted an inhibitory effect on the growth of Escherichia coli in this medium.
Bromocresol purple is less inhibitory, and the colour change from purple to yellow provides a more sensitive and definite indication of acid formation; therefore this indicator is used in Oxoid MacConkey Broth (Purple), which corresponds to the alternative formulations recommended in `The Bacteriological Examination of Water Supplies’2 and `International Standards for Drinking Water’3.
Technique
The presumptive coliform examination consists of the inoculation of measured volumes of water into tubes of MacConkey Broth (Purple) which are incubated at 35°C for 48 hours. Choice of volumes for inoculation will depend on the bacteriological grade of the water being tested; for `medium’ waters the Public Health Laboratory Service Water Committee (1961) recommend one 50ml, five 10ml and five 1ml quantities of water - 50ml and 10ml amounts being added to their own volume of double-strength MacConkey Broth while the 1ml amounts are each added to 5ml of single-strength MacConkey Broth.