Purpose: The goals of this investigation were to characterize the bacteriophages and evaluatate the use of individual and mixed bacteriophages for control of Salmonella in a cattle hide model.
Methods: Bacteriophages targeting various Salmonella serovars were isolated from three cattle feedlots located in south Texas and waste water in Texas. Bacteriophage genomes were sequenced and morphology was observed via TEM. The phage host range was tested against a panel of 20 Salmonella isolates by spot dilution tests. The ability of phages to inhibit bacterial growth was assessed in a 96-well microtiter plate assay. Cattle hides obtained at harvest were inoculated with a cattle feedlot isolated Salmonella strain and treated with single and mixed bacteriophages. The treated cattle hides were homogenized and plated to observe bacterial reduction.
Results: Bacteriophages were determined to be members of the virulent Chi-like, 9NA-like, and T5-like groups of Siphoviridae; with one phage belonging to a novel jumbo Myoviridae phage type. The host ranges of phages were highly variable, with the broadest host range phage infecting 16 of the 20 Salmonella strains tested. Certain phage combinations were found to be able to suppress the regrowth of phage-resistant bacteria in the microtiter plate assays. Salmonella was significantly reduced by some single and mixed phage treatments (n=3, P<0.05), with reductions up to 1.7 log CFU/cm2.
Significance: In this study, the ability of phages to reduce Salmonella on cattle hides suggested a novel means of suppressing transmission of Salmonella into the lymph nodes of cattle; and, thus, may be a use for controlling Salmonella in ground beef.