Characterization and regulation of AcrABR, a RND-type multidrug efflux system, in Agrobacterium tumefaciens C58

Abstract

Agrobacterium tumefaciens AcrR is the transcriptional repressor of the acrABR operon. The AcrAB efflux pump confers resistance to various toxic compounds, including antibiotics [ciprofloxacin (CIP), nalidixic acid (NAL), novobiocin (NOV) and tetracycline (TET)], a detergent [sodium dodecyl sulfate (SDS)] and a biocide [triclosan (TRI)]. The sequence to which AcrR specifically binds in the acrA promoter region was determined by EMSA and DNase I footprinting. The AcrR-DNA interaction was abolished by adding NAL, SDS and TRI. Quantitative real time-PCR analysis showed that induction of the acrA transcript occurred when wild-type cells were exposed to NAL, SDS and TRI. Indole is a signaling molecule that increases the antibiotic resistance of bacteria, at least in part, through activation of efflux pumps. Expression of the A. tumefaciens acrA transcript was also inducible by indole in a dose-dependent manner. Indole induced protection against CIP, NAL and SDS but enhanced susceptibility to NOV and TRI. Additionally, the TET resistance of A. tumefaciens was not apparently modulated by indole. A. tumefaciens AcrAB played a dominant role and was required for tolerance to high levels of the toxic compounds. Understanding the regulation of multidrug efflux pumps and bacterial adaptive responses to intracellular and extracellular signaling molecules for antibiotic resistance is essential. This information will be useful for the rational design of effective treatments for bacterial infection to overcome possible multidrug-resistant pathogens.

Triclosan: An Update on Biochemical and Molecular Mechanisms

“…These findings complement an earlier report describing enhanced resistance to TCS due to overexpressed acrAB multidrug efflux pump [58]. It was recently suggested that TCS binds to the transcriptional repressor AcrR, causing conformational changes and preventing its binding to the efflux pump AcrA promoter in Agrobacterium tumefaciens [59].…”

Biocidal Agents Used for Disinfection Can Enhance Antibiotic Resistance in Gram-Negative Species

“…Resistance in Salmonella caused by increasing concentrations of triclosan is associated with an overexpression of the AcrAB efflux pump [23]. A possible mechanism was shown with Agrobacterium tumefaciens where triclosan abolishes the interaction between the transcriptional repressor of the acrABR operon (acrR) and the DNA to which acrR specifically binds in the acrA promoter region [55]. A correlation between a decreased triclosan susceptibility and multidrug-resistance was shown in 428 Salmonella enterica isolates.…”

Coming from the Wild: Multidrug Resistant Opportunistic Pathogens Presenting a Primary, Not Human-Linked, Environmental Habitat

“…Further, A. radiobacter has been recently described to cause ocular infections, and it was identified in polymicrobial keratitis cases [ 338 ]. Although there is not much information about the intrinsic AR of these bacteria, the presence of RND efflux pumps in the genus Agrobacterium [ 339 , 340 ] suggests that these bacteria may present low susceptibility to different drugs. Further, the finding of an A. radiobacter clinical isolates carrying different antibiotic-inactivating enzymes [ 341 ] indicate that this microorganism may possess a wide set of AR determinants.…”