Multivariate Analyses Revealed Distinctive Features Differentiating Human and Cattle Isolates of Shiga Toxin-Producing Escherichia coli O157 in Japan

Genotypes of Shiga toxin-producingEscherichia coli (STEC) O157 isolated from humans and cattle were analyzed by uni- and multivariable logistic regression, and population structure methods, to gain insight into transmission and the nature of human infection. Eleven genotyping assays, including PCR typing of five virulence factors (stx 1 ,stx 2 ,stx 2c ,eae , andehxA ) and a lineage-specific polymorphism assay using six markers (LSPA6), were considered in the analyses. The prevalence of thestx 1 ,stx 2 , andstx 2c virulence factors was significantly different between human and cattle isolates. However, multivariable regression revealed that the presence of only thestx 2 gene was significantly associated with human isolates after controlling for confounding effects. LSPA6 typing demonstrated an apparent difference in the distribution of LSPA6 lineages between human and cattle isolates and a strong association betweenstx genotypes and LSPA6 genotypes. Population genetics tools identified three genetically distinct clusters of STEC O157. Each cluster was characterized bystx genotypes and LSPA6 genotypes. The human isolates typically comprised LSPA6 lineage I withstx 1 stx 2 strains and LSPA6 lineage I/II withstx 2 orstx 2 stx 2c strains. In contrast, the cattle isolates comprised LSPA6 lineage II strains withstx 2c orstx 2 stx 2c strains in addition to the clusters identified for the human isolates. Our analyses provide new evidence that thestx 2 gene is the most distinctive feature in human isolates compared to cattle isolates in Japan, and only a subset of the genetically diverse population isolated from cattle is involved in human illnesses. Our results may contribute to international comparisons and risk assessments of STEC O157.