Selective growth media

A method of selectively inhibiting the growth of non-target bacteria cells in a mixed population of target and non-target bacteria cells, the method comprising the steps of:

• (a) contacting the mixed population with a growth medium containing a selective agent comprising a carrier moiety linked to a toxic moiety;
• wherein the carrier moiety comprises an amino acid residue and is linked by a scissile peptide bond linkage to a toxic moiety comprising a 1-aminoalkyl phosphonic acid or a salt thereof;
• wherein the selective agent is able to enter non-target cells in which the scissile linkage is cleaved, releasing the toxic moiety to exert a toxic effect on the non-target cells causing inhibition of the growth of the non-target cells, whereas the scissile linkage is not cleaved in target cells or the toxic moiety, if released from the selective agent, does not exert a toxic effect on the target cell;
• and
• (b) culturing the bacteria cells in conditions which allow for growth of target cells.