Role of the acrAB locus in organic solvent tolerance mediated by expression of marA, soxS, or robA in Escherichia coli

Abstract

Escherichia coli K-12 strains are normally tolerant to n-hexane and susceptible to cyclohexane. Constitutive expression of marA of the multiple antibiotic resistance (mar) locus or of the soxS or robA gene product produced tolerance to cyclohexane. Inactivation of the mar locus or the robA locus, but not the soxRS locus, increased organic solvent susceptibility in the wild type and Mar mutants (to both n-hexane and cyclohexane). The organic solvent hypersusceptibility is a newly described phenotype for a robA-inactivated strain. Multicopy expression of mar, soxS, or robA induced cyclohexane tolerance in strains with a deleted or inactivated chromosomal mar, soxRS, or robA locus; thus, each transcriptional activator acts independently of the others. However, in a strain with 39 kb of chromosomal DNA, including the mar locus, deleted, only the multicopy complete mar locus, consisting of its two operons, produced cyclohexane tolerance. Deletion of acrAB from either wild-type E. coli K-12 or a Mar mutant resulted in loss of tolerance to both n-hexane and cyclohexane. Organic solvent tolerance mediated by mar, soxS, or robA was not restored in strains with acrAB deleted. These findings strongly suggest that active efflux specified by the acrAB locus is linked to intrinsic organic solvent tolerance and to tolerance mediated by the marA, soxS, or robA gene product in E. coli.

Commonality among Fluoroquinolone-Resistant Sequence Type ST131 Extraintestinal Escherichia coli Isolates from Humans and Companion Animals in Australia

“…The plates were sealed with petroleum jelly and laboratory film, followed by incubation at 30°C for 48 h. Growth was then recorded for each spot as confluent, visible, or absent. Controls included the E. coli strain pairs AG100-AG102 and WT-MIII (16,49). Organic solvent tolerance was scored as no growth inhibition in the presence of 100% hexane (ϩ), 3:1 hexane-cyclohexane (ϩϩ), 1:1 hexane-cyclohexane (ϩϩϩ), 1:3 hexane-cyclohexane (ϩϩϩϩ), or 100% cyclohexane (ϩϩϩϩϩ).…”

Multidrug binding properties of the AcrB efflux pump characterized by molecular dynamics simulations

“…1). These features fit with the extreme variety of substrates recognized by AcrB (6), ranging from basic dyes to most antibiotics, detergents, and even solvents (26,27). It is of crucial importance, therefore, to understand the molecular mechanism by which such a diverse range of substrates are recognized by AcrB; this can help in the design of antimicrobial agents that would not be pumped out quickly, and of better inhibitors of these pumps.…”

Susceptibilities to Antimicrobials and Disinfectants in Salmonella Isolates Obtained from Poultry and Swine in Thailand

“…those in the major facilitator (MF) superfamily, the resistance-nodulation-division (RND) family and the small multidrug resistance (SMR) family have been commonly found in Gram-negative bacteria, the RND type efflux pumps are predominant [21]. In Salmonella, the RND family AcrAB-TolC system has been shown to confer resistance to multiple antibiotics and disinfectants resulting in multiple antibiotic resistance (MAR) phenotypes [16,25]. Such MAR phenotype has been shown to be associated with cyclohexane tolerance [22].…”