Figure 3. Relative expression of genes involved in stress response on E. coli K-12 AG100 strain in the presence of 25 μg/ml of PMZ at pH 5 and pH 7 at different time points (1-18 h). At the beginning of the culturing period most of the studied genes showed a decreased expression pattern. Increase in gene expression level was detected in the cases of the acrA and B, marR, soxS, sdiA genes after the 18th hour at pH 5. Significant gene expression could be observed in the expression levels of acrA, acrB, and marA genes in the 18th hour, of marB in the 1st hour and of ftsI after 4 h. Initially the efflux pump genes acrA and acrB were down-regulated, but at the end of the culturing period (18th hour) both genes were up-regulated at pH 7. The significant correlation is: p≤0.05.