Psychrotrophic Bacteriophages for Beef Spoilage Pseudomonads ¹

A total of 40 beef spoilage pseudomonads was used as bacterial hosts for the isolation of psychrotrophic bacteriophages (phages) from spoiled rib steaks. Thirty-eight homologous phages, lytic for 25 of these hosts, were isolated and purified. An additional 12 bacterial isolates were susceptible to heterologous phage lysis and only three of the bacteria examined were resistant to lysis by any of the phage tested. On the basis of heterologous cross-sensitivity to phages, the meatborne Pseudomonas strains and 4 identified ATCC Pseudomonas hosts were differentiated into 37 distinct phage lysotypes. In addition, Pseudomonas phages were found to inhibit bacterial growth in tryptic soy broth by significantly extending the lag phase under psychrotrophic conditions (7°C). However, the incubation of bacteria with phages resulted in the selection of phage resistant bacterial mutants.