Fig. 1. Overexpression of AcrAB increases the spontaneous mutation frequency.

(A) Schematic showing an increase in spontaneous mutations in cells with higher efflux pump expression. (B) Rifampicin mutation frequency in E. coli wild-type and ΔacrB strains with and without acrAB overexpression. n ≥ 8 biological replicates. (C) Rifampicin mutation frequency in S. Typhimurium (S. Tm) LT2. n ≥ 12 biological replicates. (D) Ciprofloxacin, tetracycline, and chloramphenicol mutation frequencies in E. coli ΔacrB. n ≥ 5 biological replicates. The ΔacrB strain in (D) did not produce any mutants in the presence of any of the antibiotics; mutants were observed for all antibiotics in the acrAB overexpression strain. For (B) to (D), blue bars show the median values, gray boxes indicate the interquartile range, and whiskers show the maximum and minimum values. Box plot raw data are shown in fig. S9A. Strains without acrAB overexpression contained an equivalent plasmid expressing cfp in place of acrAB. *P < 0.05; **P < 0.01;***P < 0.001, Mann-Whitney rank sum test.