INCREASING PHAGE RESISTANCE OF CHEESE STARTERS - A CASE-STUDY USING LACTOCOCCUS-LACTIS DPC4268

This study serves as an example of strategies used to increase the pha ge resistance of an important Irish Cheddar cheese starter, Lactococcu s lactis DPC4268. It describes the emergence and persistence of a lyri c bacteriophage, 4268, that has a relatively large burst size and exhi bits no homology to the most common phage types encountered in Irish c heese plants. Inherent difficulties were encountered that prevented th e effective introduction of conjugative phage-resistance plasmids pNP4 0 and pMRC01 to strain DPC4268. In fact, pNP40-associated Abi systems were naturally present in six of 19 starters. Control of phage 4268 wa s eventually achieved by generating a mutant of DPC4268, which was sub sequently used for cheese manufacture.