milk products. lactose is milk sugar.

Digest or process lactose, a consituent of milk.

Organic milk is less likely to contain pesticides, hormones, and antibiotic residues. The fact that these things are not found in organic milk may be the reason that there was not any issues when drinking the organic milk. To be completely free from any issues due to lactose intolerance it would be best to get a lactose free milk such as Lactaid brand milk.

milk

MacConkey agar is yellow (due to the lactose in the agar). When an organism consumes the lactose, the agar turns purple. Purple indicates a positive test.

If the organism doesn't use the agar, the agar stays yellow.