Table 1

Activity of various substrates of the AcrAB efflux system

AgentAcrAB-mediated resistance*ChargepKaIC50 for fluorescent lipid extrusion, μMt1/2 for ΔpH dissipation in AcrB vesicles, mint1/2 for transmembrane diffusion,§ sec
Novobiocin324.3ND2.3<2
Fusidic acid325.4NDND<2
Cloxacillin2562.71151.28.5
Erythromycin32+8.81102.66
Chloramphenicol8No charge1.9ND
GlycochenodeoxycholateND4.250ND23
GlycocholateND4.01051.5>1,200
Taurocholate>161.9151.0>1,200
  • * Figures represent the ratio between the minimal inhibitory concentration of acrAb+ parent strain and that of the ΔacrAB mutant strain (7, 8, 13, 14). ND, not determined. 

  • From Fig. 3

  • Not determined because stock solutions at high concentrations could not be prepared at pH 6.0. 

  • No activity detected in the range tested. 

  • From Fig. 4

  • § Measured as described in text, by adding drugs (up to 0.2 mM) to AcrB-free vesicles at pH 7.0 and ΔpH = 0.