Resistance of phages lytic to pathogenic Escherichia coli to sanitisers used by the food industry and in home settings

Summary Phages are potentially useful as antimicrobial agents in food‐processing environments, provided they can remain active upon extended storage and in the presence of sanitisers. Survival of six phages lytic against enteropathogenic (EPEC) and shiga‐toxigenic (STEC) Escherichia coli strains was assessed upon storage at 4 °C, −20 °C and −70 °C in phosphate‐buffered‐saline (PBS) and Tris‐magnesium‐gelatine buffer (TMG) for up to 1 year. The phages were also exposed to ethanol, sodium hypochlorite, peracetic acid, quaternary ammonium chloride (biocide A), hydrogen peroxide/peracetic acid/peroctanoic acid (biocide B), p‐toluensulfonchloroamide (biocide D) and alkaline chloride foam (biocide C). Plaque‐forming units remained unchanged when the phages were stored at 4 °C in both buffers tested, but decreased by 3.5 and 5.7 log10 PFU when stored in PBS at −20 and −70 °C, respectively. Moreover, TMG seems to be the most protective suspension medium with decreasing temperature because a 1−log10 PFU reduction was observed at −20 and −70 °C. Incubation in 100% ethanol for 24 h reduced plaque counts only by 2.5 log10 PFU. In 10 ppm of sodium hypochlorite and in biocide B (0.13%), the counts decreased by ~5 and ~6 log10 PFU after 15 min. Finally, biocide A and D reduced counts by 4 and 2–4 log10 PFU after 30 min and 8 h of incubation, respectively. Phages were completely inactivated only by peracetic acid and biocides C and E. Therefore, the phages evaluated might be potentially applied together with classical sanitisers such as ethanol and industrial biocides A, B and D, in disinfection programs against pathogenic STEC and EPEC strains. Resistance of coliphages to sanitisers.