Isolation and characterization of lactococcal bacteriophages from cultured buttermilk plants in the United States

From July 1993 and June 1994, 27 different lactococcal bacteriophages were isolated from 27 US cultured buttermilk plants located in 23 states. Phages were characterized by DNA homology, electron microscopy, restriction patterns, genome size, host range, and serology. Over 80% (22 of 27) of the phages were classified into the 936 species, and the remaining phages were divided almost equally between the P335 species (3 of 27) and the c2 species (2 of 27). The 936 and c2-type phages had the same basic morphological and genetic characteristics as other phages from the same species isolated in other countries. Very closely related 936 phages were isolated from widely separated areas in the US. The P335 phages had a very narrow host range and showed noticeable genetic and immunological diversity. None of the phages could propagate on the two exopolysaccharide-producing Lactococcus Lactis strains tested. Novel mechanisms for phage resistance should be tested for efficiency against members of the lactococcal phage species 936, c2, and P335. To our knowledge, this study is the first thorough examination of industrial lactococcal phages isolated from buttermilk plants.