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

Abstract

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.