Figure 2: Influence of active efflux on temocillin activity.
(a) Cumulative MIC distribution of temocillin in a subset of the collection (n = 124) selected to cover the whole range of MICs and influence of the efflux pump inhibitor PAβN (20 mg/L). (b) Fold reduction (log2 scale) in temocillin MIC in the presence of PAβN, according to temocillin MICs for the same isolates. The graph shows the box and whiskers plot with 10-90 percentiles, with the red line connecting the medians. (c) Kinetics of NPN efflux from PAO1 or PAO1mexAB in the absence (control) or presence of temocillin (TMO) at the indicated concentrations. Vmax are expressed in reduction in the fluorescence signal per second. (d) Kinetics of efflux of NPN as a function of temocillin MIC for the 32 isolates for which mexA and mexB were sequenced (Table 1). The ordinate is expressed as the Vmax (arbitrary fluorescence units). R2 for a one-phase association: 0.9043. Node splitting value for slower efflux: MIC of 256 mg/L or lower (LogWorth statistic: 29.5157 [p < 0.001]). (e,f) MIC and rate of NPN efflux in sequenced isolates classified according to the type of mutations observed in mexA and mexB (Table 1). ‘Truncated/aberrant’ refer to deletions of more than 3 consecutive nucleotides in the sequence, nonstop mutations, insertion of minisatellites or aberrant signal peptides. ‘Missense mutations’ refer to mutations leading to the replacement of at least one amino acid in the corresponding protein. The graphs shows individual values together with means and SD. Statistical analysis (1-way ANOVA; Tuckey post-hoc test): data series with different letters are different from one another (p < 0.05).
