Variation in Stress Resistance Patterns among stx Genotypes and Genetic Lineages of Shiga Toxin-Producing Escherichia coli O157

To evaluate the relationship between bacterial genotypes and stress resistance patterns, we exposed 57 strains of Shiga toxin-producingEscherichia coli (STEC) O157 to acid, freeze-thaw, heat, osmotic, oxidative, and starvation stresses. Inactivation rates were calculated in each assay and subjected to univariate and multivariate analyses, including principal component analysis (PCA) and cluster analysis. Thestx genotype was determined for each strain as was the lineage-specific polymorphism assay (LSPA6) genotype. In univariate analyses, strains of thestx 1 stx 2 genotype showed greater resistance to heat than strains of thestx 1 stx 2c genotype; moreover, strains of thestx 1 stx 2 genotype showed greater resistance to starvation than strains of thestx 2 orstx 2c genotypes. LSPA6 lineage I (LI) strains showed greater resistance to heat and starvation than LSPA6 lineage II (LII) strains. PCA revealed a general trend that a strain with greater resistance to one type of stress tended to have greater resistance to other types of stresses. In cluster analysis, STEC O157 strains were grouped into stress-resistant, stress-sensitive, and intermediate clusters. Instx genotypes, all strains of thestx 1 stx 2 genotype were grouped with the stress-resistant cluster, whereas 72.7% (8/11) of strains of thestx 1 stx 2c genotype grouped with the stress-sensitive cluster. In LI strains, 77.8% (14/18) of the strains were grouped with the stress-resistant cluster, whereas 64.7% (11/17) of LII strains were grouped with the stress-sensitive cluster. These results indicate that the genotypes of STEC O157 that are frequently associated with human illness, i.e., LI or thestx 1 stx 2 genotype, have greater multiple stress resistance than do strains of other genotypes.