CT production profiles of single-SNP strains and double-, triple-, and quadruple-SNP combination strains. CT production profiles of single-SNP strains and double-, triple-, and quadruple-SNP combination strains. SNPs and SNP combinations were introduced into the WT strain N16961, and average fold changes in CT production levels relative to the CT production in WT N16961 were calculated. Other controls included MQ1795 (hypervirulent clinical isolate) and O395ΔtoxT (negative control). Strains containing the different SNPs and SNP combinations introduced into WT N16961 are indicated by the numbers beginning with “MS” found in Table 2. The presence of SNPs identified in genes in the indicated clinical isolates is denoted by a “+,” whereas the WT N16961 version of a SNP is denoted by a “−.” A two-tailed Student t test yielded P values of ≤0.05 (*), <0.005 (**), and <0.0005 (***). Bailey M. Carignan et al. mSphere 2016; doi:10.1128/mSphere.00253-16