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AcrAB multidrug efflux pump regulation in Salmonella enterica serovar Typhimurium by RamA in response to environmental signals.

Nikaido E, Yamaguchi A, Nishino K - J. Biol. Chem. (2008)

Bottom Line: Among these pumps, AcrAB is effective in generating drug resistance and has wide substrate specificity.Other regulators of acrAB such as MarA, SoxS, Rob, SdiA, and AcrR did not contribute to acrAB induction by indole in Salmonella.Our results suggest that RamA controls the Salmonella AcrAB-TolC multidrug efflux system through dual regulatory modes in response to environmental signals.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Membrane Biology, Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.

ABSTRACT
Salmonella enterica serovar Typhimurium has at least nine multidrug efflux pumps. Among these pumps, AcrAB is effective in generating drug resistance and has wide substrate specificity. Here we report that indole, bile, and an Escherichia coli conditioned medium induced the AcrAB pump in Salmonella through a specific regulator, RamA. The RamA-binding sites were located in the upstream regions of acrAB and tolC. RamA was required for indole induction of acrAB. Other regulators of acrAB such as MarA, SoxS, Rob, SdiA, and AcrR did not contribute to acrAB induction by indole in Salmonella. Indole activated ramA transcription, and overproduction of RamA caused increased acrAB expression. In contrast, induction of ramA was not required for induction of acrAB by bile. Cholic acid binds to RamA, and we suggest that bile acts by altering pre-existing RamA. This points to two different AcrAB regulatory modes through RamA. Our results suggest that RamA controls the Salmonella AcrAB-TolC multidrug efflux system through dual regulatory modes in response to environmental signals.

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Multidrug efflux genes in Salmonella enterica serovar Typhimurium induced by an E. coli conditioned medium. The tolC-lac (EG15109), acrAB-lac (NKS505), acrEF-lac (EG15114), acrD-lac (EG15120), mdtABC-lac (EG15124), mdsABC-lac (NKS517), emrAB-lac (NKS522), mdfA-lac (NKS524), mdtK-lac (EG15132), and macAB-lac (NKS530) strains were grown in conditioned medium prepared from E. coli culture. Expression levels of multidrug efflux genes were determined by β-galactosidase assay. The data correspond to mean values of three independent experiments. Error bars correspond to the standard deviation. Asterisks indicate statistically significant differences (*, p < 0.01) in the paired Student's t test.
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fig4: Multidrug efflux genes in Salmonella enterica serovar Typhimurium induced by an E. coli conditioned medium. The tolC-lac (EG15109), acrAB-lac (NKS505), acrEF-lac (EG15114), acrD-lac (EG15120), mdtABC-lac (EG15124), mdsABC-lac (NKS517), emrAB-lac (NKS522), mdfA-lac (NKS524), mdtK-lac (EG15132), and macAB-lac (NKS530) strains were grown in conditioned medium prepared from E. coli culture. Expression levels of multidrug efflux genes were determined by β-galactosidase assay. The data correspond to mean values of three independent experiments. Error bars correspond to the standard deviation. Asterisks indicate statistically significant differences (*, p < 0.01) in the paired Student's t test.

Mentions: Conditioned Medium from E. coli Induces Salmonella acrAB and tolC Genes via the RamA Regulator—Indole accumulates and MdtEF is induced in stationary phase cultures of E. coli, but experiments with a tnaAB mutant showed that indole partially contributes to this induction (48). These results indicate that E. coli produces indole as well as other efflux pump inducers. Therefore, we investigated whether an E. coli conditioned medium would induce multidrug efflux pumps in Salmonella. Conditioned medium, prepared from E. coli MG1655, significantly induced eight Salmonella multidrug efflux pumps, including acrAB and the outer membrane protein gene tolC (Fig. 4). Inductions of acrAB and tolC were significantly decreased in ΔramA (Fig. 5, A and B), indicating that the E. coli conditioned medium induced acrAB and tolC via the RamA regulator.


AcrAB multidrug efflux pump regulation in Salmonella enterica serovar Typhimurium by RamA in response to environmental signals.

Nikaido E, Yamaguchi A, Nishino K - J. Biol. Chem. (2008)

Multidrug efflux genes in Salmonella enterica serovar Typhimurium induced by an E. coli conditioned medium. The tolC-lac (EG15109), acrAB-lac (NKS505), acrEF-lac (EG15114), acrD-lac (EG15120), mdtABC-lac (EG15124), mdsABC-lac (NKS517), emrAB-lac (NKS522), mdfA-lac (NKS524), mdtK-lac (EG15132), and macAB-lac (NKS530) strains were grown in conditioned medium prepared from E. coli culture. Expression levels of multidrug efflux genes were determined by β-galactosidase assay. The data correspond to mean values of three independent experiments. Error bars correspond to the standard deviation. Asterisks indicate statistically significant differences (*, p < 0.01) in the paired Student's t test.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2527123&req=5

fig4: Multidrug efflux genes in Salmonella enterica serovar Typhimurium induced by an E. coli conditioned medium. The tolC-lac (EG15109), acrAB-lac (NKS505), acrEF-lac (EG15114), acrD-lac (EG15120), mdtABC-lac (EG15124), mdsABC-lac (NKS517), emrAB-lac (NKS522), mdfA-lac (NKS524), mdtK-lac (EG15132), and macAB-lac (NKS530) strains were grown in conditioned medium prepared from E. coli culture. Expression levels of multidrug efflux genes were determined by β-galactosidase assay. The data correspond to mean values of three independent experiments. Error bars correspond to the standard deviation. Asterisks indicate statistically significant differences (*, p < 0.01) in the paired Student's t test.
Mentions: Conditioned Medium from E. coli Induces Salmonella acrAB and tolC Genes via the RamA Regulator—Indole accumulates and MdtEF is induced in stationary phase cultures of E. coli, but experiments with a tnaAB mutant showed that indole partially contributes to this induction (48). These results indicate that E. coli produces indole as well as other efflux pump inducers. Therefore, we investigated whether an E. coli conditioned medium would induce multidrug efflux pumps in Salmonella. Conditioned medium, prepared from E. coli MG1655, significantly induced eight Salmonella multidrug efflux pumps, including acrAB and the outer membrane protein gene tolC (Fig. 4). Inductions of acrAB and tolC were significantly decreased in ΔramA (Fig. 5, A and B), indicating that the E. coli conditioned medium induced acrAB and tolC via the RamA regulator.

Bottom Line: Among these pumps, AcrAB is effective in generating drug resistance and has wide substrate specificity.Other regulators of acrAB such as MarA, SoxS, Rob, SdiA, and AcrR did not contribute to acrAB induction by indole in Salmonella.Our results suggest that RamA controls the Salmonella AcrAB-TolC multidrug efflux system through dual regulatory modes in response to environmental signals.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Membrane Biology, Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.

ABSTRACT
Salmonella enterica serovar Typhimurium has at least nine multidrug efflux pumps. Among these pumps, AcrAB is effective in generating drug resistance and has wide substrate specificity. Here we report that indole, bile, and an Escherichia coli conditioned medium induced the AcrAB pump in Salmonella through a specific regulator, RamA. The RamA-binding sites were located in the upstream regions of acrAB and tolC. RamA was required for indole induction of acrAB. Other regulators of acrAB such as MarA, SoxS, Rob, SdiA, and AcrR did not contribute to acrAB induction by indole in Salmonella. Indole activated ramA transcription, and overproduction of RamA caused increased acrAB expression. In contrast, induction of ramA was not required for induction of acrAB by bile. Cholic acid binds to RamA, and we suggest that bile acts by altering pre-existing RamA. This points to two different AcrAB regulatory modes through RamA. Our results suggest that RamA controls the Salmonella AcrAB-TolC multidrug efflux system through dual regulatory modes in response to environmental signals.

Show MeSH
Related in: MedlinePlus