FIG 1.

Relative expression levels of pbp5 and vanB ligase in the naive TC-A transconjugant (TCA P0) or in the resulting selected ones (TCA-A P9, which was continuously passaged in the presence of ampicillin for ∼400 generations, and TCA-V P13, which was continuously passaged in the presence of vancomycin for ∼400 generations). The parental strains (D344RRF and C68) were included for comparison. The parents and the three versions of TC-A were grown with either ampicillin or vancomycin, and relative expression was calculated using the levels of expression for the corresponding group without antibiotic treatment. Expression levels of 16S rRNA were used to normalize the data. Error bars indicate the standard errors of the means for biological triplicates. (A) pbp5 expression is not modified with respect to that for the control (untreated cells) in the presence of half the MIC of ampicillin. pbp5 expression was induced in C68 and the three different TC-A groups in the presence of vancomycin. (B) vanB ligase expression was very low in the absence of vancomycin. In the presence of the antibiotic, there was a significant induction of vanB ligase expression. Unpassaged TC-A (P0) had lower vanB ligase expression levels than C68 and the passaged groups, which correlates with a lower vancomycin MIC. White bars, BHI-grown cells (calibrator); gray bars, ampicillin-grown cells; black bars, vancomycin-grown cells. ****, P < 0.0001; ***, P < 0.0002; *, P < 0.05.