Variation in virulence among clades of Escherichia coli O157:H7 associated with disease outbreaks

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Fig. 1.

Genetic relatedness of E. coli O157 among 403 O157 and closely related O55:H7 strains based on 96 SNPs. (A) The location of 83 genes within 96 SNP loci on the E. coli O157:H7 genomic map of the Sakai strain. Real-time PCR assays detected 52 loci with nonsynonymous polymorphisms (black circles), 43 loci with synonymous polymorphisms (white circles), and one locus (uidA-686) with a GG insertion (open triangle). (B) The distribution of nucleotide diversity (π) across 96 SNP loci. Diversity ranges from 0 for two monomorphic SNP loci to a maximum between 0.45 and 0.50 for 26 loci. The average π for the 96 loci is 0.212 ± 0.199. (C) Phylogenetic relationships among SNP genotypes (SGs) using the minimum evolution algorithm based on the distance matrix of pairwise differences between SGs. The consensus tree is shown with the percentages at the nodes of the >70% bootstrap confidence values based on 1,000 replicates. Both the GUD⁺ and Sor⁺, which occur in clade 9, are negative (GUD⁻ and Sor⁻) in the derived clades 1–8.