Figure 3.

Quantification of the relative mRNA expression levels of a panel of efflux pump genes. Strains were grown in MGIT tubes for the MGIT 960 system in the presence of half MIC of each antibiotic as follows: MtbPT3 was exposed to isoniazid; MtbPT5 was exposed to rifampicin; MtbBR1 was exposed to ofloxacin; H37Rv, MtbPT7, and MtbPT11 were exposed to isoniazid or rifampicin. The relative expression of the efflux pump genes was assessed by comparison of the relative quantity of the respective mRNA in the presence of an antibiotic to the non-exposed strain. A level of relative expression equal to 1 indicates that the expression level was identical to the strain that was being compared (gray dashed line in the graphs). Genes showing expression levels above 1 were considered to be expressed; genes showing expression levels above two were considered to be significant overexpressed. The results were considered significant when ^*P < 0.05; and highly significant when ^**P < 0.01 and ^***P < 0.001.