Insight into Shiga toxin genes encoded by XXXX O157 from whole genome sequencing.

@entity1 @entity5555 @entity221 @entity526
The ability of Shiga toxin-producing @entity526 (STEC) to cause severe @entity221 in @entity1 is determined by multiple host factors and bacterial characteristics, including Shiga toxin (Stx) subtype. Given the link between Stx2a subtype and disease severity, we sought to identify the stx subtypes present in @entity5555 ( @entity5555 ) of 444 isolates of STEC O157. Difficulties in assembling the stx genes in some strains were overcome by using two complementary bioinformatics methods: mapping and de novo assembly. We compared the @entity5555 analysis with the results obtained using a PCR approach and investigated the diversity within and between the subtypes. All strains of STEC O157 in this study had stx1a, stx2a or stx2c or a combination of these three genes. There was over 99% (442/444) concordance between PCR and @entity5555 . When common source strains were excluded, 236/349 strains of STEC O157 had multiple copies of different Stx subtypes and 54 had multiple copies of the same Stx subtype. Of those strains harbouring multiple copies of the same Stx subtype, 33 had variants between the alleles while 21 had identical copies. Strains harbouring Stx2a only were most commonly found to have multiple alleles of the same subtype (42%). Both the PCR and @entity5555 approach to stx subtyping provided a good level of sensitivity and specificity. In addition, the @entity5555 data also showed there were a significant proportion of strains harbouring multiple alleles of the same Stx subtype associated with clinical disease in England.
