Scientific Publications by FDA Staff

Appl Environ Microbiol 2015 Jan 15;81(2):569-77

Genomic diversity and virulence characterization of historical Escherichia coli O157 strains isolated from clinical and environmental sources.

Rump LV, Gonzalez-Escalona N, Ju W, Wang F, Cao G, Meng S, Meng J

Escherichia coli O157:H7 is, to date, the major E. coli serotype causing food-borne human disease worldwide. Strains of O157 with other H antigens have also been recovered. We analyzed a collection of historic O157 strains (N=400) isolated in the late 1980's - early 1990's in the United States. Strains were predominantly serotype O157:H7 (55%), and various O157:non-H7 (41%) not previously reported regarding their pathogenic potential. Although lacking Shiga-toxin (stx) and eae genes, serotypes O157:H1, H2, H11, H42, and H43 carried several virulence factors (iha, terD, hlyA) also found in virulent serotype E. coli O157:H7. Pulse field gel electrophoresis (PFGE) showed the O157 serogroup was diverse, with strains with the same H-type clustering together closely. Among non-H7 isolates, Serotype O157:H43 was highly prevalent (65%) and carried important enterohemorrhagic E. coli (EHEC) virulence markers (iha, terD, hlyA, espP). Isolates from two particular H-types, H2 and H11, among the most commonly found non-O157 EHEC (O26:H11, O111:H11, O103:H2/H11, O45:H2), unexpectedly clustered more closely with O157:H7 than other H-types, and carried several virulence genes. This suggests an early divergence of the O157 serogroup to clades with different pathogenic potential. Appearance of important EHEC virulence markers in closely related H-types suggests their virulence potential and suggests further monitoring of those serotypes not implicated in severe illness thus far.