FIG 5.

Role of MexXY on tobramycin resistance of ΔlasR and fusA1 G61A mutants. (A) mexX transcript levels were determined by droplet digital PCR and normalized to the housekeeping control gene proC. Strains were wild-type PA14 or PA14 with the fusA1 G61A substitution. Each strain had either an intact lasR (LasR⁺, filled circles) or ΔlasR (LasR⁻, open circles). Each point represents in independent experiment; horizontal lines represent the geometric mean, and the vertical lines represent the geometric standard deviation. Statistical analysis by two-way ANOVA showed a significant interaction between the effects of strain and lasR allele on mexX transcripts (P < 0.005, F_1,8 = 15.67). An additional Sidak’s post hoc test comparing PA14 and fusA1 G61A of the LasR⁺ strains revealed no significance (P > 0.6). (B and C) The MIC of tobramycin was determined for each strain carrying intact lasR (LasR⁺, black bars) or ΔlasR (LasR⁻, white bars). Results are the average of three independent experiments and the vertical bars show standard deviation. In pairwise comparisons with the LasR^+/− PA14 strains, there was a significant interaction between the effects of strain and lasR allele for T1 (P < 0.01 and F_(1,8) = 29.01 for panel B and P < 0.005 and F_(1,8) = 17.99 for panel C) but not for the other strains. In panels A to C, pairwise comparisons of LasR⁺ and LasR⁻ of each strain were determined using Sidak’s post hoc test with P-values adjusted for multiple comparisons. *, P < 0.05; ***, P < 0.001; ****, P < 0.0001; ns, not significant.