pH indicator in agar plates

[ilovebiology77]

Hi there, I'm about to conduct an experiment where I look at the effect of sugar on the shelf life of yoghurt. I plan to measure this by quantifying the number of lactic acid bacteria in each sample by using bromocresol purple pH indicator.

However, before I do the experiment, I was wondering what kinds of problems I can expect using bromocresol purple indicator in the MRS agar in terms of errors and practicality so I can minimise these problems??

I plan to use 0.025ml per litre.

Also, I've never used this indicator before so what can I expect in terms of the colour the agar will be when I add it to the plates? Will it be initially all purple and after incubation, there will be some yellow colonies signifying lactic acid bacteria?

Really really appreciate the help!

Many thanks!

A