Salmonella Host Range of Bacteriophages That Infect Multiple Genera

Abstract

Conventionally, bacteriophages are considered viruses capable of amplification only in a narrow range of closely related bacteria. Presently, we selected bacteriophages with the ability to infect more than 1 bacterial genus. Initially, wild-type bacteriophages were selected for ability to form plaques in Salmonella enteritidis agar overlays. For determination of host specificity, a pool of 44 bacteriophages was combined with each bacterial isolate in tryptic soy broth. This mixture was incubated with fresh bacterial culture and media for 4 sequential passes, and the resulting bacteriophage titer was determined using S. enteritidis. One Klebsiella and 3 different Escherichia isolates successfully amplified some bacteriophage(s) from the S. enteritidis-selected bacteriophage pool (experiment 1). Amplification of bacteriophages in each species was confirmed by the formation of increased plaque forming units in a tryptic soy agar overlay with the enteric (alternative host) bacteria, Klebsiella or Escherichia (experiment 2). Two selected bacteriophages, confirmed to amplify in Escherichia or Klebsiella, were further evaluated for ability to amplify in 10 different Salmonella serovars by amplification in broth culture (experiment 3). One had the ability to amplify in 6 different Salmonella serovars, and the other had the ability to amplify in 2 different Salmonella serovars. These experiments suggest that bacteriophage host range is not always genera-restricted and that selection of subpopulations of bacteriophages capable of amplification in alternative genera may provide a tool for selection of broad host-range bacteriophages for the pathogen of interest. Selection of non-pathogenic host isolates to support replication of Salmonella bacteriophages may allow improved safety for bacteriophage application to poultry because this would reduce the necessity for 100% purification of the bacteriophages(s) from resistant host bacteria.