Comparative analysis of virulence genes, genetic diversity, and phylogeny of Shiga toxin 2g and heat-stable enterotoxin STIa encoding Escherichia coli isolates from humans, animals, and environmental sources.

Abstract An analysis for stx 2 variants among the 2010 human stx 2 -positive Shiga toxin-producing Escherichia coli (STEC) strains from Germany collected at the National Reference Centre 1999–2008 revealed 0.6% to possess the recently described stx 2g gene. Sequencing of the whole stx 2g operons showed new alleles and pseudogenes. The further molecular, phenotypic, and phylogenetic comparison of 12 human stx 2g -harbouring isolates with 12 stx 2g -harbouring isolates from animals or environmental sources demonstrated that both groups are closely related, indicating the human infections as a potential zoonotic disease. Although originating from various different sources, the stx 2g -containing strains belong to only 3 phylogenetic lineages, represented by 4 serovars belonging to 4 sequence types. In view of the huge diversity among other STEC, this suggests the emergence of the stx 2g variant as a rather recent microevolutionary event. Interestingly, in the strains under investigation, Stx2g was not expressed. However, all of them contained the estIa gene which typically is associated with enterotoxin-producing E. coli and did express STIa. By this combination of virulence genes of different pathotypes of intestinal pathogenic E. coli , these strains represent a new, intermediate pathotype and emerging pathogens. Given a rising number of intermediate pathotypes becoming described among E. coli , a wider range of virulence markers should be included in the regular pathotype diagnostics.