Bacteriophage biocontrol of Shiga toxigenic Escherichia coli (STEC) O145 biofilms on stainless steel reduces the contamination of beef

Abstract

Shiga toxigenic Escherichia coli (STEC) can form biofilms and frequently cause serious foodborne illnesses. A strain of STEC O145:H25 (EC19990166) known to be a strong biofilm former was used to evaluate the efficacy of bacteriophage AZO145A against biofilms formed on stainless steel (SS) coupons. Exposure of STEC O145:H25 to phage AZO145A (1010PFU/mL) for 2h resulted in a 4.0 log10 reduction (P<0.01) of planktonic cells grown in M9 broth at 24°C for 24h, while reductions were 2.0 log10CFU/mL if these cells were grown for 48h or 72h prior to phage treatment. STEC O145 biofilms formed on SS coupons for 24, 48 and 72h were reduced (P<0.01) 2.9, 1.9 and 1.9 log10CFU/coupon by phages. STEC O145cells in biofilms were readily transferred from the surface of the SS coupon to beef (3.6 log10CFU/coupon) even with as little as 10s of contact with the meat surface. However, transfer of STEC O145cells from biofilms that formed on SS coupons for 48h to beef was reduced (P<0.01) by 3.1 log10CFU by phage (2×1010PFU/mL) at 24°C. Scanning electron microscopy revealed that bacterial cells within indentations on the surface of SS coupons were reduced by phage. These results suggest that bacteriophage AZO145A could be effective in reducing the viability of biofilm-adherent STEC O145 on stainless steel in food industry environments.