Phage resistance in Streptococcus lactis ssp. diacetylactis transconjugant SLA3.2501 and its derivatives.

Phage 18-16, which was virulent for Streptococcus lactis ssp. diacetylactis SLA3.25 was used to study phage-resistant characteristics of mucoid S. lactis ssp. diacetylactis transconjugant SLA3.2501 obtained through conjugative cotransfer of pSRQ2201 (Lac-plasmid) and pSRQ2202 (Muc-plasmid) to SLA3.25 (15). Interaction of phage 18-16 with SLA3.2501 and its derivatives showed that phage resistance was not related to either the lack of phage adsorption or restriction-modification. Suppression of phage replication in SLA3.2501 and its derivatives was not completely relieved by curing of either pSRQ2201 or pSRQ2202 or both.