Low-Density Macroarray Targeting Non-Locus of Enterocyte Effacement Effectors ( nle Genes) and Major Virulence Factors of Shiga Toxin-Producing Escherichia coli (STEC): a New Approach for Molecular Risk Assessment of STEC Isolates

Rapid and specific detection of Shiga toxin-producingEscherichia coli (STEC) strains with a high level of virulence for humans has become a priority for public health authorities. This study reports on the development of a low-density macroarray for simultaneously testing the genesstx 1 ,stx 2 ,eae , andehxA and six differentnle genes issued from genomic islands OI-122 (ent ,nleB , andnleE ) and OI-71 (nleF ,nleH1 -2 , andnleA ). Various strains ofE. coli isolated from the environment, food, animals, and healthy children have been compared with clinical isolates of various seropathotypes. Theeae gene was detected in all enteropathogenicE. coli (EPEC) strains as well as in enterohemorrhagicE. coli (EHEC) strains, except in EHEC O91:H21 and EHEC O113:H21. The geneehxA was more prevalent in EHEC (90%) than in STEC (42.66%) strains, in which it was unequally distributed. Thenle genes were detected only in some EPEC and EHEC strains but with various distributions, showing thatnle genes are strain and/or serotype specific, probably reflecting adaptation of the strains to different hosts or environmental niches. One characteristicnle gene distribution in EHEC O157:[H7], O111:[H8], O26:[H11], O103:H25, O118:[H16], O121:[H19], O5:H−, O55:H7, O123:H11, O172:H25, and O165:H25 wasent/espL2 ,nleB ,nleE ,nleF ,nleH1 -2 ,nleA . (Brackets indicate genotyping of theflic orrfb genes.) A secondnle pattern (ent/espL2 ,nleB ,nleE ,nleH1 -2 ) was characteristic of EHEC O103:H2, O145:[H28], O45:H2, and O15:H2. The presence ofeae ,ent/espL2 ,nleB ,nleE , andnleH1 -2 genes is a clear signature of STEC strains with high virulence for humans.