Escherichia coli O157:H7 is an endemic pathogen causing a variety of human diseases including mild diarrhea, hemorrhagic colitis, hemolytic-uremic syndrome, and thrombotic thrombocytopenic purpura. This study concerns the exploitation of bacteriophages as biocontrol agents to eliminate the pathogen E. coli O157:H7. Two distinct lytic phages (e11/2 and e4/1c) isolated against a human strain of E. coli O157:H7, a previously isolated lytic phage (pp01), and a cocktail of all three phages were evaluated for their ability to lyse the bacterium in vivo and in vitro. Phage e11/2, pp01, and the cocktail of all three virulent phages resulted in a 5-log-unit reduction of pathogen numbers in 1 h at 37°C. However, bacteriophage-insensitive mutants (BIMs) emerged following the challenge. All tested BIMs had a growth rate which approximated that of the parental O157 strain, although many of these BIMs had a smaller, more coccoid cellular morphology. The frequency of BIM formation (10 ؊6 CFU) was similar for e11/2, pp01, and the phage cocktail, while BIMs insensitive to e4/1c occurred at the higher frequency (10 ؊4 CFU). In addition, BIMs commonly reverted to phage sensitivity within 50 generations. In an initial meat trial experiment, the phage cocktail completely eliminated E. coli O157:H7 from the beef meat surface in seven of nine cases. Given that the frequency of BIM formation is low (10 ؊6 CFU) for two of the phages, allied to the propensity of these mutants to revert to phage sensitivity, we expect that BIM formation should not hinder the use of these phages as biocontrol agents, particularly since low levels of the pathogen are typically encountered in the environment.

A truncated derivative of the phage endolysin LysK containing only the CHAP (cysteine-and histidinedependent amidohydrolase/peptidase) domain exhibited lytic activity against live clinical staphylococcal isolates, including methicillin-resistant Staphylococcus aureus. This is the first known report of a truncated phage lysin which retains high lytic activity against live staphylococcal cells.

Aims:  To screen Irish faecal samples from a variety of sources with a view to isolating novel anti‐Salmonella phages and to subsequently evaluate their lytic capability. Methods and Results:  Two novel anti‐Salmonella phages st104a and st104b were isolated from a screening programme based on their lytic capability. The phages produced significantly larger plaques (2 mm) on the chosen indicator Salmonella enterica strain, DPC6046, when compared with the well‐known control phage, Felix 01 (0·5 mm). Both phages st104a and st104b were found to have a broad host range within the Salm. enterica species. During in vitro trials, both phages (st104a and st104b) reduced Salm. enterica numbers more than 99% within 1 h. In vivo studies, involving the addition of the phage to porcine gastric juice (pH 2·5) demonstrated that phage st104a and phage Felix 01 were capable of surviving (10 and 30% survival respectively) the acidic conditions, unlike st104b, which was undetectable after 2 h exposure. Conclusions:  Two novel lytic anti‐Salmonella phages were isolated and characterized. Significance and Impact of the Study:  With the exception of phage Felix 01, there has been relatively little phage therapy work performed using lytic Salmonella phage. In this study, the lytic phages st104a and st104b were isolated as a result of a faecal screening programme. Subsequently, phage st104a was found to have potential for biocontrol of Salm. enterica numbers if administered orally to pigs given their survival in porcine gastric juice, whereas, phage st104b may have potential in reducing cell numbers if applied by alternative approaches.