Psychrotrophic Brocothrix thermosphacta bacteriophages isolated from beef.

A total of 15 wild-type Brocothrix thermosphacta strains isolated from beef and the type strain, B. thermosphacta ATCC 11509, were used as hosts for the isolation of bacteriophages under psychrotrophic conditions (7 degrees C). A total of 21 virulent, psychrotrophic phages were successfully isolated and purified from aqueous extracts of spoiled rib steaks. Phage plaque size and plating efficiency significantly increased as incubation temperature was reduced from 25 to 1 degree C. Electron microscopy of two homologous B. thermosphacta phages showed the virions to consist of hexagonal heads and tails, with terminal appendages clearly visible on one of the phages. On the basis of culture and biochemical data, the wild-type B. thermosphacta strains had characteristics identical to those of strain ATCC 11509. However, specific differences in the pattern of susceptibilities to the phages revealed the presence of 14 distinct phage lysotypes. Phage typing may provide a rapid and sensitive means of differentiating B. thermosphacta strains.