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

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.This study was supported by project PhageSTEC (POCI-01-0145-FEDER-029628) funded by FEDER through COMPETE2020 (Programa Operacional Competitividade e Internacionalização) and by National Funds thought FCT (Fundação para a Ciência e a Tecnologia).