RamA Confers Multidrug Resistance in Salmonella enterica via Increased Expression of acrB , Which Is Inhibited by Chlorpromazine

Abstract

Salmonella enterica serovar Typhimurium SL1344, in which efflux pump genes (acrB, acrD, acrF, tolC) or regulatory genes thereof (marA, soxS, ramA) were inactivated, was grown in the presence of 240 antimicrobial and nonantimicrobial agents in the Biolog Phenotype MicroArray. Mutants lacking tolC, acrB, and ramA grew significantly worse than other mutants in the presence of 48 agents (some of which have not previously been identified as substrates of AcrAB-TolC) and particularly poorly in the presence of phenothiazines, which are human antipsychotics. MIC testing revealed that the phenothiazine chlorpromazine had antimicrobial activity and synergized with common antibiotics against different Salmonella serovars and SL1344. Chlorpromazine increased the intracellular accumulation of ethidium bromide, which was ablated in mutants lacking acrB, suggesting an interaction with AcrB. High-level but not low-level overexpression of ramA increased the expression of acrB; conferred resistance to chloramphenicol, tetracycline, nalidixic acid, and triclosan and organic solvent tolerance; and increased the amount of ethidium bromide accumulated. Chlorpromazine induced the modest overproduction of ramA but repressed acrB. These data suggest that phenothiazines are not efflux pump inhibitors but influence gene expression, including that of acrB, which confers the synergy with antimicrobials observed.

AraC/XylS Family Stress Response Regulators Rob, SoxS, PliA, and OpiA in the Fire Blight Pathogen Erwinia amylovora

“…The regulation of the acrAB genes has been studied extensively in human-pathogenic enterobacteria. Several members of the AraC/XylS family, including MarA, RamA, Rob, and SoxS, have been identified as positive transcriptional regulators of this efflux system (10,13,14,21,54,58). In this study, we identified four regulators from the plant pathogen E. amylovora that are closely related to the MarA/Rob/ SoxS group of AraC/XylS transcriptional activators from E. coli (see Fig.…”

“…Previous studies have shown that high-level expression of AraC/XylS regulators is required to induce antibiotic resistance in enteric bacteria (52)(53)(54). Therefore, we generated high-copynumber plasmids overexpressing the pliA, rob, soxS, and opiA genes from their native promoters.…”

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

“…Several investigators have studied the important roles of AcrAB in bacterial drug resistance and virulence; however, the regulation mechanism of acrAB in Salmonella in response to extracellular signals has not been well characterized. AcrAB regulation is mediated by five regulators: MarA, SoxS, Rob, AcrR and RamA (Bailey et al, 2008;Ma et al, 1996;Randall & Woodward, 2002;Rosenberg et al, 2003;Schneiders et al, 2003). In Salmonella, AcrAB regulation in response to indole, bile salts and E. coli metabolites depends on RamA (Nikaido et al, 2008).…”

“…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).…”

Evaluation of different lignocellulosic biomass pretreatments by phenotypic microarray-based metabolic analysis of fermenting yeast

“…However, the presence of furan compounds (such as furfural) is an unavoidable consequence of the use of relatively high temperatures (>140ºC) to break LCM into fermentable sugars (Tomás-Pejó et al, 2010). Additionally, the higher temperature steam explosion methods (220ºC) may generate up to 8 mM furfural (Bailey et al, 2008). This can significantly reduce the ethanol yields achieved or reduce the volumetric productivity (the ethanol output per unit time) thus reducing the process efficiency.…”