Phage biocontrol of enteropathogenic and S higa toxin‐producing Escherichia coli during milk fermentation

Two bacteriophages, isolated from faeces, were assayed as biocontrol agents of pathogenic E scherichia coli during milk fermentation. Phage DT 1 was tested on the strain E . coli DH 5α, one enteropathogenic E . coli ( EPEC ) strain and one S higa toxigenic E . coli O 157: H 7 ( STEC ) strain. Phage DT 6 was tested on two STEC strains ( O157 : H 7 and non‐ O 157). One additional assay was performed by using a cocktail of both phages against the O 157: H 7 STEC strain. S treptococcus thermophilus 10‐ C , the strain used as lactic starter, reached 10 9  CFU ml −1 after 4 h, while pH values fell to 4·5 after 8 h, regardless of the presence of E . coli strains and/or phages. In absence of phages, E . coli strains reached 4–6 log CFU ml −1 at 5–6 h. Escherichia coli DH5 α and O 157: H 7 STEC strains were rapidly and completely inactivated by phage DT 1 and phage cocktail, respectively, while O 157: H 7 STEC was completely inactivated either by DT 1 or by DT 6, after 8 h. The EPEC strain was not detected at 1 h (<10 CFU ml −1 ) but grew afterwards, though at lower rates than without phage. For non‐ O 157: H 7 STEC , reductions lower than 1 log CFU ml −1 were observed for all sampling times. Phages DT 1 and DT 6, either individually or as a cocktail, effectively reduce O 157: H 7 STEC counts during milk fermentation, without compromising the starter culture performance. Significance and Impact of the Study Coliphages DT 1 and DT 6, isolated from faeces and selected on the basis of their host range, showed to be valuable tools for the control of pathogenic E scherichia coli during milk fermentation, without compromising the starter culture performance. Both phages, either individually or as a cocktail, may function as an extra safety barrier beyond traditional pasteurization, effectively reducing O 157: H 7 Shiga toxin‐producing Escherichia coli ( STEC ) counts during early growth, thus avoiding Shiga toxin production and accumulation.