Sean Clarke/Lab technique notes

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MacConkey is a pH sensitive dye, and (indirectly) measures the ability of a strain to metabolize the sugar source on the plate (in our experiments, either arabinose or lactose). Strains that can metabolize the sugar are RED on the plate (sugar metabolism produces acid), whereas strains that cannot metabolize the sugar are WHITE (as these strains use amino acids for carbon◊high pH).

Xgal is a substrate for the enzyme B-galactosidase (Bgal), the protein product of the lacZ gene. Strains that are producing Bgal are BLUE on plates containing Xgal, whereas strains that cannot produce Bgal are WHITE on these plates.

Kan and Cm are abbreviations for Kanamycin and Chloramphenicol, respectively. These are both antibiotics. Strains that are “resistant” to these antibiotics (e.g. KanR) will grow on plates containing the antibiotic; strains that are “sensitive” (KanS) will not grow on these plates.