Purpose: The objective of this study was to determine if application of lytic bacteriophages reduced the loads of O157 and nonO157 STEC on inoculated cattle hides under conditions simulating live animal intervention application.
Methods: Hide pieces (65.6±6.5 cm2) were inoculated with a gelatin-based slurry containing a cocktail (9.7±0.1 log CFU/ml) of E. coli serotypes O157:H7, O26:H11, O45:H2, O111, O121:H19, and O145. After a 30 min attachment, excess slurry was removed by scraping gelatin off the surface, and hides were treated with a water or phage intervention by a hand-held trigger spray bottle applying treatment. A commercial phage intervention containing 108 PFU/ml phages was diluted to 107 PFU/ml and compared to an untreated controls and sterile distilled water. The intervention was allowed to dwell for 60 min at 37°C, after which surviving STEC were enumerated from hide pieces on tryptic soy agar supplemented with rifampicin and cycloheximide (100 mg/ml each). Plating of STEC survivors was completed following centrifugation and suspension of STEC in fresh diluent to separate nonadsorbed lytic phages from noninfected STEC.
Results: The mean number of STEC attaching to inoculated hides was 6.8±0.1 log CFU/cm2 prior to intervention application across two replications (n=6); mean phage titer was 8.4±0.8 log PFU/ml. Mean counts of STEC posttreatment were 6.8±0.1 log for H2O and phage treatments, respectively (P>0.05); no effective reduction in STEC by either treatment was observed compared with the control.
Significance: Although no differences were detected between positive control hide samples compared to treated hide samples, phages may enhance beef safety, though further optimization of phage interventions is still required.