Prevalence and control of Shiga toxin-producing E. coli: from diversity in dairy cattle to phage therapy

Abstract

Shiga toxin-producing E. coli (STEC) strains are important foodborne pathogens worldwide, transmitted from ruminant to humans through contaminated food. Their control is still a challenge as most E. coli in nature are commensal and, thus, controlling strategies should target only pathogenic strains/serotypes. Bacteriophages (bacterial viruses) can cope with this challenge by allowing a tailored intervention. We performed an epidemiological study of STEC at 21 milk farms across the Northern region of Portugal and evaluated the potential of bacteriophage therapy to control the well-known O157 STEC serotype. From 409 dairy cattle analyzed, STEC strains were more prevalent in heifers (45 %) than in lactating cows (16 %). STEC isolates with several stx1 and stx2 subtypes were identified and they belonged to 73 different O:H serotypes. Regarding bacteriophage therapy evaluation, an O157-specific phage (CBA120), was tested in vitro and in vivo. The bacteriophage reduced STEC in contaminated ruminant fluids of rumen and intestine (>4 logs) as well as STEC biofilms adhered with intestinal mucosa (>2 logs). Moreover, bacteriophage treatments significantly reduced E. coli O157:H7 numbers (1 log) in artificially contaminated sheep, comparatively with the mockedtreated group. Overall, results suggest the potential use of bacteriophages to control STEC in vivo.