Characterization and application of phages isolated from sewage for reduction of Escherichia coli O157:H7 in biofilm

Two phages of Escherichia coli O157:H7 from a sewage sample were isolated and characterized to control E. coli O157:H7 in foods. The isolated phages, BECP2 and BECP6, belonged to the Myoviridae and Podoviridae, respectively. Their burst sizes were 33 PFU/cell for BECP2 and 51 PFU/cell for BECP6 after a latent period of 25 min. Shiga toxin genes were not detected on either the BECP2 or BECP6 phage. The two phages were susceptible to 70% ethanol. To determine the utility of the two phage mixture for biocontrol of E. coli O157:H7, we analyzed the reduction of E. coli O157:H7 in commercial milk and in biofilms. The mixture reduced the growth of E. coli O157:H7 from 6 log CFU/mL to 1 log CFU/mL after 5-h incubation at 37 °C in commercial milk. The mixture was applied to E. coli O157:H7 in a biofilm formed on glass wool, microtiter plate, and stainless steel coupon. The density of E. coli O157:H7 in the biofilm reduced from OD600 1.1 to 0.6 on the plate and from 6 log CFU/coupon to 2 log CFU/coupon on the coupon. Therefore, the BECP2 and BECP6 phages might be efficient sanitizing agents for reducing E. coli O157:H7 in a biofilm environment.