The local repressor AcrR plays a modulating role in the regulation of <i>acrAB genes of Escherichia coli</i> by global stress signals

Ma, Dzwokai; Alberti, Marie; Lynch, C; Nikaido, Hiroshi; Hearst, John E.

doi:10.1046/j.1365-2958.1996.357881.x

Cited by 358 publications

(312 citation statements)

References 39 publications

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“…Recently, Nakajima et al (20) showed that overexpression of RobA in E. coli produced multiple resistance to antibiotics and heavy metals, including Ag. Since RobA activates the transcription of acrAB efflux pump genes (13), it may also increase the expression of a similar efflux system that is capable of pumping out heavy metal ions.…”

Section: Discussionmentioning

confidence: 99%

Silver-resistant mutants of Escherichia coli display active efflux of Ag+ and are deficient in porins

1997

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Silver-resistant mutants were selected by stepwise exposure of silver-susceptible clinical strains of Escherichia coli, two of which did not contain any plasmids, to either silver nitrate or silver sulfadiazine. These mutants showed complete cross-resistance to both compounds. They showed low-level cross-resistance to cephalosporins and HgCl 2 but not to other heavy metals. The Ag-resistant mutants had decreased outer membrane (OM) permeability to cephalosporins, and all five resistant mutants tested were deficient in major porins, either OmpF or OmpF plus OmpC. However, the well-studied OmpF-and/or OmpC-deficient mutants of laboratory strains K-12 and B/r were not resistant to either silver compound. Resistant strains accumulated up to fourfold less 110m AgNO 3 than the parental strains. The treatment of cells with carbonyl cyanide m-chlorophenylhydrazone increased Ag accumulation in Ag-susceptible and -resistant strains, suggesting that even the wild-type Ag-susceptible strains had an endogenous Ag efflux activity, which occurred at higher levels in Ag-resistant mutants. The addition of glucose as an energy source to starved cells activated the efflux of Ag. The results suggest that active efflux, presumably coded by a chromosomal gene(s), may play a major role in silver resistance, which is likely to be enhanced synergistically by decreases in OM permeability.Silver (Ag) is a biologically nonessential metal which is used widely in photographic emulsions. The toxicity of Ag has also led to clinical applications, including the topical treatment of bacterial infections with silver nitrate (AgNO 3 ) and silver sulfadiazine (AgSD). The action of AgNO 3 and AgSD is assumed to be dependent on the Ag ϩ ions, which strongly inhibit bacterial growth through poisoning of respiratory enzymes and electron transport components and through interference with DNA functions (3, 18).Ag-resistant bacterial strains have been isolated from both clinical and environmental sources. Examples include strains of Acinetobacter baumannii (4), Escherichia coli (7), Enterobacter cloacae (7), Klebsiella pneumoniae (7), Pseudomonas aeruginosa (19), Pseudomonas stutzeri (5), and Salmonella typhimurium (15). In some cases the resistance was shown to be encoded by plasmids (4,5,15,27,31).Mechanisms of resistance to other metals such as arsenic, cadmium, copper, and mercury have been elucidated at the molecular level (for reviews, see references 3, 27, and 28). Resistance is sometimes due to enzymatic detoxification as in the case of mercury and organomercurials (28). But in a majority of cases energy-dependent ion efflux seems to be responsible, as exemplified by bacterial resistance to many oxyanions (such as arsenite, antimonite, and chromate) as well as to the cations zinc, cobalt, cadmium, and nickel (3, 27, 28). Solioz and Odermatt (30) have shown recently that a P-type copper efflux ATPase from a gram-positive bacterium, Enterococcus hirae, can also pump out, perhaps fortuitously, Ag ϩ . Little is known, however, about the mechanism of Ag...

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Section: Discussionmentioning

confidence: 99%

Silver-resistant mutants of Escherichia coli display active efflux of Ag+ and are deficient in porins

1997

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“…Therefore, we investigated the induction pathway of acrAB in Salmonella in response to paraquat. In addition to RamA, AcrAB is regulated by three activators, MarA, SoxS and Rob, Salmonella AcrAB regulation by indole and paraquat and one repressor, AcrR (Ma et al, 1996;Randall & Woodward, 2002;Rosenberg et al, 2003). We used deletion mutants of these regulators to investigate whether they were required for acrAB induction in response to paraquat.…”

Section: Paraquat Induces Acrab Via the Soxs Regulator And Not Via Thmentioning

confidence: 99%

“…The acrAB regulation mechanism must be examined to understand the physiological role of AcrAB. In Escherichia coli, AcrAB is regulated by three activators, MarA, SoxS and Rob, and one repressor, AcrR (Ma et al, 1996;Randall & Woodward, 2002;Rosenberg et al, 2003). In Salmonella, RamA is involved in inducing acrAB in addition to the (Bailey et al,2008 ;Schneiders et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Regulation of the AcrAB multidrug efflux pump in Salmonella enterica serovar Typhimurium in response to indole and paraquat

et al. 2011

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Salmonella enterica serovar Typhimurium has at least nine multidrug efflux pumps. Among these, AcrAB is constitutively expressed and is the most efficient, playing a role in both drug resistance and virulence. The acrAB locus is induced by indole, Escherichia coli-conditioned medium, and bile salts. This induction is dependent on RamA through the binding sequence in the upstream region of acrA that binds RamA. In the present study, we made a detailed investigation of the ramA and acrAB induction mechanisms in Salmonella in response to indole, a biological oxidant for bacteria. We found that acrAB and ramA induction in response to indole is dependent on RamR. However, the cysteine residues of RamR do not play a role in the induction of ramA in response to indole, and the oxidative effect of indole is therefore not related to ramA induction via RamR. Furthermore, we showed that paraquat, a superoxide generator, induces acrAB but not ramA. We further discovered that the mechanism of acrAB induction in response to paraquat is dependent on SoxS. The data indicate that there are at least two independent induction pathways for acrAB in response to extracellular signals such as indole and paraquat. We propose that Salmonella utilizes these regulators for acrAB induction in response to extracellular signals in order to adapt itself to environmental conditions.

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“…The proteins in this family bind in the vicinity of the promoters of their respective target genes (8,14). To examine whether MphR(A) is the repressor protein that controls expression of mph(A), we constructed an mphR(A) expression system and purified MphR(A).…”

Section: Specific Binding Of Mphr(a) To the Promoter Region Of Mph(a)mentioning

confidence: 99%

Regulation of Transcription of themph(A) Gene for Macrolide 2′-Phosphotransferase I inEscherichia coli: Characterization of the Regulatory GenemphR(A)

et al. 2000

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The local repressor AcrR plays a modulating role in the regulation of acrAB genes of Escherichia coli by global stress signals

Cited by 358 publications

References 39 publications

Silver-resistant mutants of Escherichia coli display active efflux of Ag+ and are deficient in porins

Silver-resistant mutants of Escherichia coli display active efflux of Ag+ and are deficient in porins

Regulation of the AcrAB multidrug efflux pump in Salmonella enterica serovar Typhimurium in response to indole and paraquat

Regulation of Transcription of themph(A) Gene for Macrolide 2′-Phosphotransferase I inEscherichia coli: Characterization of the Regulatory GenemphR(A)

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