Conjugally Transferable Phage Resistance Activities from Lactococcus lactis DRC1

Lactococcus lactis ssp. lactis strain HID600 is a phage-resistant transconjugant produced by mating HID113 (an antibiotic-resistant variant of plasmid-free strain LM0230) with L. lactis ssp. lactis strain DRC1. Analysis of HID600 revealed that it had conjugally acquired phage resistance, bacteriocin production, proteolytic activity, and a 131-kb plasmid. The interaction of phages c2 and sk1 with HID113 and HID600 was studied. Plaque assays indicated that only about 12.5% of c2 infections of HID600 produced infective centers and that c2 infections of HID600 had a longer latent period and smaller average burst size than did infections of HID113. Less than .2% of sk1 infections of HID600 were apparently productive; no burst was detected. The resistance to phage infection involved restriction-modification and abortive infection effects. Such resistance might be useful in the construction of cheese starter strains with reduced susceptibility to phage infection, although phage variants able to infect HID600 with increased efficiency were observed. © 1992, American Dairy Science Association. All rights reserved.