Association of Virulence Genotype with Phylogenetic Background in Comparison to Different Seropathotypes of Shiga Toxin-Producing Escherichia coli Isolates

The distribution of virulent factors (VFs) in 287 Shiga toxin-producingEscherichia coli (STEC) strains that were classified according to Karmali et al. into five seropathotypes (M. A. Karmali, M. Mascarenhas, S. Shen, K. Ziebell, S. Johnson, R. Reid-Smith, J. Isaac-Renton, C. Clark, K. Rahn, and J. B. Kaper, J. Clin. Microbiol. 41:4930-4940, 2003) wasinvestigated. The associations of VFs with phylogenetic background wereassessed among the strains in comparison with the differentseropathotypes. The phylogenetic analysis showed that STEC strainssegregated mainly in phylogenetic group B1 (70%) and revealed thesubstantial prevalence (19%) of STEC belonging to phylogenetic group A(designated STEC-A). The presence of virulent clonal groups inseropathotypes that are associated with disease and their absence fromseropathotypes that are not associated with disease support the conceptof seropathotype classification. Although certain VFs (eae ,stx 2-EDL933 ,stx 2-vha , andstx 2-vhb ) were concentrated in seropathotypesassociated with disease, others (astA , HPI,stx 1c , andstx 2-NV206 )were concentrated in seropathotypes that are not associated withdisease. Taken together with the observation that the STEC-A group wasexclusively composed of strains lackingeae recovered fromseropathotypes that are not associated with disease, the“atypical” virulence pattern suggests that STEC-Astrains comprise a distinct category of STEC strains. A practicalbenefit of our phylogenetic analysis of STEC strains is thatphylogenetic group A status appears to be highly predictive of“nonvirulent”seropathotypes.