Bio-control of Shiga Toxin-producing Escherichia coli (STEC) O157:H7 Contaminated in Raw Beef by Using a Lytic Bacteriophage

Introduction: Shiga Toxin-producing Escherichia coli (STEC) are dangerous foodborne pathogens usually transmitted to humans through raw or undercooked meats. Lytic bacteriophages or phages have recently emerged as the natural agents for controlling of STEC contamination in meats.

Purpose: The objectives of this study are to isolate lytic bacteriophages for STEC O157:H7 and to use them as the means for the decontamination of these bacteria in raw beef.

Methods: The lytic phages were isolated from bovine intestine samples by using the double layer technique with E. coli O157 as the hosts for propagation. The phage with widest lytic range was selected and used for the inactivation of STEC O157:H7 bacteria artificially inoculated in raw beef at 5 x 10⁵ CFU/piece at 8°C and 25°C. The survival viable cells were then enumerated after 2, 4, 6 and 24 h incubation for comparing the differences between control and phage-treated samples. The significant differences were inferred by using t-test.

Results: The phage PE37 belonging to the non-stx gene member of the Myoviridae family was successfully isolated. The lytic range tests revealed that the PE37 lysed all 37/37 (100%) tested STEC O157:H7 strains isolated from human illness. At 8°C, after 24 h incubation, the treatment of raw beef pieces (n = 10) with the PE37 at Multiplicity of Infection (MOI) = 100 reduced the concentration of STEC O157:H7 by 0.82 log CFU/piece compared to phage-free control (P < 0.05). Likewise, the reduction of STEC O157:H7 viable count was approximately 3.1 log CFU/piece in the samples treated with the phage compared to non-treatment at 25°C after 24 h (P < 0.05).

Significance: The results from present study implicate that phage PE37 has potential characteristics applicable to controlling of STEC O157:H7 contamination in raw meats.