FIG 1.

Generation of persisters and analysis of dnaE2 expression in persister cells. (A) Survival of M. smegmatis cultures upon treatment with 10 μg/mL of ciprofloxacin (Cip) or 50 μg/mL of rifampicin (Rif) for 48 h. Viable counts were determined by serial dilution and plating. The mean survival rates ± standard deviations (SD) from five independent replicates were plotted using GraphPad Prism software. Percent survival is calculated as the ratio of viable cells at 48 h to those at 0 h and is depicted above each treatment. (B) M. smegmatis with a dual reporter was treated with Cip or Rif. After 72 h of incubation, an aliquot of the culture was subjected to confocal microscopy along with the untreated control. The experiment was repeated at least three times. (C) The intensity profile of dnaE2 expression was plotted by estimating the signal intensity of mCherry from ∼30 individual cells from 3 different fields. A.U, arbitrary units. (D) Triplicate cultures of wild-type M. smegmatis were treated with Cip and Rif for 6 h, along with the untreated control. Total RNA was isolated, followed by cDNA synthesis and qRT-PCR analysis of the recA and dnaE2 transcripts. Variations in gene expression in comparison with the untreated controls are represented as fold changes (2^−ΔΔCT) on the graph (*, P value of <0.05; **, P value of <0.01).