Effect of the MS Bacteriophage on STEC O157:H7 Populations in Beef

Objectives: This research was conducted to evaluate the killing efficiency of the Mello-Shebs (MS) O157:H7 bacteriophage against three strains of STEC O157:H7 in vitro and on beef surface under aerobic conditions. Materials and Methods: Killing efficiency of bacteriophage MS O157:H7 (University of Nevada, Reno - Meat Science library) was tested against three strains including ATCC® 43895TM (stx1 and stx2 positive), ATCC® 43894TM (stx1 and stx2 positive), and Micreos 128. To determine the efficiency of the phage in vitro, each strain of STEC O157:H7 was incubated at 37°C overnight and then diluted to achieve 1500 CFU/mL. Subsequently, 0.1 ml of this dilution was plated in quadruplicate onto 1.6% LB agar plates. The experimental plates received 0.1 ml of phage solution at 108 PFU/ml. The plates were incubated at 37°C for 24 h and the resulting colonies were counted and compared to controls to determine killing efficiency of the phage against each STEC strain. In order to evaluate the effect of bacteriophage application on beef, m. cutaneous trunci (rose meat, IMPS 194) were sourced from a USDA inspected facility, fabricated into 100 cm2 and randomly assigned to either control or treatment groups. Samples were inoculated with a STEC cocktail to result in a contamination level of approximately 3 log CFU/cm2 on meat surfaces after swabbing. After bacterial attachment for 30 min at 7°C, control samples were treated with BPW and experimental samples were treated with the phage solution at 108 PFU/ml. After dwelling for 1 hour at 7°C, samples were swabbed and the resulting 1 mL was thoroughly vortexed, serial diluted, and plated onto LB plates. The plates were incubated at 37°C for 24 h and the resulting colonies were counted. Data was analyzed by SAS whereas means were separated by LSMEANS and differences were indicated using DIFF functions. Results: In vitro killing efficiency of bacteriophage MS O157:H7 was determined to be 85%, 98.89%, and 97.16% for ATCC® 43894TM, ATC