We want to make two plasmids:
Plasmid #1 - A constitutive promoter with LacZ and LacY.
Plasmid #2 - A lactose inducible promoter with lysozyme and holin.
The general idea is to overexpress LacY (Lactose transporter) with LacZ (Beta-Galactosidase). When lactose is present, the cell will uptake lactose and will flip on the Lac promoter repressed by lacI when enough lactose is present. We then express lysozyme and holin which will lyse the cell releasing beta-gal cleaving lactose into glucose and galactose. Glucose and galactose will then be taken up by the host in the colon.