Science Buddies: "Ask an Expert"

I am attempting to measure the effect of B. thuringiensis on the growth and treatment of Candida albicans. In the beginning, we tried to measure the growth using ImageJ and then differentiating the C. albicans from other colonies by looking at the color difference. Now, I can't do that because Candida has the same color as Bacillus, so we cannot differentiate between the 2 colors. I tried to use a chromogenic agar such as CHROMagar candida, but those types of agar contain an antibiotic, which makes acillus impossible to grow. Is there any way to stain the Candida colonies without affecting anything else on the petri dish (B. thuringiensis)? Thanks.

You are examining the activity of an insecticidal bacillus, Bacillus thuringiensis (Bt), on a a human pathogenic yeast, Candida albicans (Ca). What is the rationale for this?

You said you had agar that was specific for Candida so why don't you simply mix Bt and Ca, let them incubate together for some time (hours?), do serial dilutions and count the number of Ca colonies on the special agar compared to the number of colonies without Bt treatment. You don't need colonies of Bt since your read-out is colony numbers of Ca, or am I misunderstanding your experiment.

Sybee