Characterisation, antimicrobial resistance and diversity of atypical EPEC and STEC isolated from cow's milk, cheese and dairy cattle farm environments

This study was carried out to determine the occurrence and characteristics of enteropathogenic Escherichia coli (EPEC) and Shiga toxin-producing E. coli (STEC) strains in cow's milk, cheese and dairy cattle farm environments, and to estimate distribution of antimicrobial resistance. A collection of 18 atypical EPEC -aEPEC, 14 STEC, and one E. albertii was obtained and characterized from 502 samples. Occurrence of aEPEC in cow's milk was high (>6%) whereas non-O157 STEC was isolated in ca. 2% of milk samples. Detection of these diarrheagenic E. coli was absent in more than 100 cheese samples obtained from raw milk. This is the first report identifying E. albertii (O69:HNM) in a dairy cattle farm. Nearly one-third of aEPEC strains showed antimicrobial resistance, mostly presenting a multidrug resistance pattern. One clonal complex (ST20 Cplx) containing aEPEC strains from milk and faecal samples was determined. Two STEC strains belonged to serotypes with importance in human disease (O91:H21 and O55:H8) and were isolated from air samples which suggests a high dissemination potential. Spanish bulk tank cow's milk can constitute an important source of aEPEC strains besides STEC, bearing multiple antimicrobial resistance and with high diversity of both serotypes and genetic features linked to potential human infection.