Scientific Publications by FDA Staff

J Clin Microbiol 2015 Nov;53(11):3466-73

Simultaneous presence of insertion sequence-excision enhancer (IEE) and insertion sequence IS629 correlates with increased diversity and virulence in Shiga-toxin producing Escherichia coli (STEC).

Toro M, Rump LV, Cao G, Meng J, Brown EW, Gonzalez-Escalona N

Although new serotypes of enterohemmorrhagic Escherichia coli (EHEC) emerge constantly, the mechanisms by which these new pathogens arise and why emerging serotypes tend to carry more virulence genes than other E. coli are not understood. An insertion sequence (IS) excision enhancer (IEE) was discovered in EHEC O157:H7, promoting the excision of IS3 family members, and generating various genomic deletions. One IS3 family member, IS629, actively transposes and proliferates in EHEC O157:H7 and enterotoxigenic E. coli (ETEC) O139 and O149. The simultaneous presence of IEE/IS629 (and other IS3 family members) could be part of a system promoting not only adaptation and genome diversification in E. coli O157:H7, but also contributing to the development of pathogenicity among predominant serotypes. Prevalence comparisons of these elements in 461 strains, representing 72 different serotypes and 5 pre-assigned seropathotypes (SPT) A-E, showed that presence of both elements simultaneously was serotype-specific and associated with highly pathogenic serotypes (O157 and top non-O157 STEC) implicated in both outbreaks and sporadic cases of human illness (SPT A and B). Serotypes lacking one or both elements were less likely to have been isolated from clinical cases. Our comparisons of IEE sequences showed sequence variations that could be divided into at least three clusters. Interestingly, the IEE sequences from O157 and top 10 non-O157 STEC serotypes fell into Clusters I and II, while less commonly isolated serotypes O5 and O174 fell into Cluster III. These results suggest that IS629 and IEE elements could be acting synergistically to promote genome plasticity and genetic diversity among STEC, enhancing their abilities to adapt to hostile environments and rapidly take up virulence factors.