Beyond Antimicrobial Resistance: Evidence for a Distinct Role of the AcrD Efflux Pump in <italic toggle="yes">Salmonella</italic> Biology

ABSTRACT For over 20 years, bacterial multidrug resistance (MDR) efflux pumps have been studied because of their impact on resistance to antimicrobials. However, critical questions remain, including why produce efflux pumps under non-antimicrobial treatment conditions, and why have multiple pumps if...

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Autores principales:	Michelle M. C. Buckner, Jessica M. A. Blair, Roberto M. La Ragione, Jane Newcombe, Daniel J. Dwyer, Alasdair Ivens, Laura J. V. Piddock
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Lenguaje:	EN
Publicado:	American Society for Microbiology 2016
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/c418bdbe44684db7a3104372910a266e
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spelling	oai:doaj.org-article:c418bdbe44684db7a3104372910a266e2021-11-15T15:50:16ZBeyond Antimicrobial Resistance: Evidence for a Distinct Role of the AcrD Efflux Pump in <italic toggle="yes">Salmonella</italic> Biology10.1128/mBio.01916-162150-7511https://doaj.org/article/c418bdbe44684db7a3104372910a266e2016-12-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01916-16https://doaj.org/toc/2150-7511ABSTRACT For over 20 years, bacterial multidrug resistance (MDR) efflux pumps have been studied because of their impact on resistance to antimicrobials. However, critical questions remain, including why produce efflux pumps under non-antimicrobial treatment conditions, and why have multiple pumps if their only purpose is antimicrobial efflux? Salmonella spp. possess five efflux pump families, including the resistance-nodulation-division (RND) efflux pumps. Notably, the RND efflux pump AcrD has a unique substrate profile, distinct from other Salmonella efflux pumps. Here we show that inactivation of acrD results in a profoundly altered transcriptome and modulation of pathways integral to Salmonella biology. The most significant transcriptome changes were central metabolism related, with additional changes observed in pathogenicity, environmental sensing, and stress response pathway expression. The extent of tricarboxylic acid cycle and fumarate metabolism expression changes led us to hypothesize that acrD inactivation may result in motility defects due to perturbation of metabolite concentrations, such as fumarate, for which a role in motility has been established. Despite minimal detectable changes in flagellar gene expression, we found that an acrD mutant Salmonella enterica serovar Typhimurium isolate was significantly impaired for swarming motility, which was restored by addition of fumarate. The acrD mutant outcompeted the wild type in fitness experiments. The results of these diverse experiments provide strong evidence that the AcrD efflux pump is not simply a redundant system providing response resilience, but also has distinct physiological functions. Together, these data indicate that the AcrD efflux pump has a significant and previously underappreciated impact on bacterial biology, despite only minor perturbations of antibiotic resistance profiles. IMPORTANCE Efflux pumps in Gram-negative bacteria are studied because of their important contributions to antimicrobial resistance. However, the role of these pumps in bacterial biology has remained surprisingly elusive. Here, we provide evidence that loss of the AcrD efflux pump significantly impacts the physiology of Salmonella enterica serovar Typhimurium. Inactivation of acrD led to changes in the expression of 403 genes involved in fundamental processes, including basic metabolism, virulence, and stress responses. Pathways such as these allow Salmonella to grow, survive in the environment, and cause disease. Indeed, our data show that the acrD mutant is more fit than wild-type Salmonella under standard lab conditions. We hypothesized that inactivation of acrD would alter levels of bacterial metabolites, impacting traits such as swarming motility. We demonstrated this by exogenous addition of the metabolite fumarate, which partially restored the acrD mutant’s swarming defect. This work extends our understanding of the role of bacterial efflux pumps.Michelle M. C. BucknerJessica M. A. BlairRoberto M. La RagioneJane NewcombeDaniel J. DwyerAlasdair IvensLaura J. V. PiddockAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 7, Iss 6 (2016)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Michelle M. C. Buckner Jessica M. A. Blair Roberto M. La Ragione Jane Newcombe Daniel J. Dwyer Alasdair Ivens Laura J. V. Piddock Beyond Antimicrobial Resistance: Evidence for a Distinct Role of the AcrD Efflux Pump in <italic toggle="yes">Salmonella</italic> Biology
description	ABSTRACT For over 20 years, bacterial multidrug resistance (MDR) efflux pumps have been studied because of their impact on resistance to antimicrobials. However, critical questions remain, including why produce efflux pumps under non-antimicrobial treatment conditions, and why have multiple pumps if their only purpose is antimicrobial efflux? Salmonella spp. possess five efflux pump families, including the resistance-nodulation-division (RND) efflux pumps. Notably, the RND efflux pump AcrD has a unique substrate profile, distinct from other Salmonella efflux pumps. Here we show that inactivation of acrD results in a profoundly altered transcriptome and modulation of pathways integral to Salmonella biology. The most significant transcriptome changes were central metabolism related, with additional changes observed in pathogenicity, environmental sensing, and stress response pathway expression. The extent of tricarboxylic acid cycle and fumarate metabolism expression changes led us to hypothesize that acrD inactivation may result in motility defects due to perturbation of metabolite concentrations, such as fumarate, for which a role in motility has been established. Despite minimal detectable changes in flagellar gene expression, we found that an acrD mutant Salmonella enterica serovar Typhimurium isolate was significantly impaired for swarming motility, which was restored by addition of fumarate. The acrD mutant outcompeted the wild type in fitness experiments. The results of these diverse experiments provide strong evidence that the AcrD efflux pump is not simply a redundant system providing response resilience, but also has distinct physiological functions. Together, these data indicate that the AcrD efflux pump has a significant and previously underappreciated impact on bacterial biology, despite only minor perturbations of antibiotic resistance profiles. IMPORTANCE Efflux pumps in Gram-negative bacteria are studied because of their important contributions to antimicrobial resistance. However, the role of these pumps in bacterial biology has remained surprisingly elusive. Here, we provide evidence that loss of the AcrD efflux pump significantly impacts the physiology of Salmonella enterica serovar Typhimurium. Inactivation of acrD led to changes in the expression of 403 genes involved in fundamental processes, including basic metabolism, virulence, and stress responses. Pathways such as these allow Salmonella to grow, survive in the environment, and cause disease. Indeed, our data show that the acrD mutant is more fit than wild-type Salmonella under standard lab conditions. We hypothesized that inactivation of acrD would alter levels of bacterial metabolites, impacting traits such as swarming motility. We demonstrated this by exogenous addition of the metabolite fumarate, which partially restored the acrD mutant’s swarming defect. This work extends our understanding of the role of bacterial efflux pumps.
format	article
author	Michelle M. C. Buckner Jessica M. A. Blair Roberto M. La Ragione Jane Newcombe Daniel J. Dwyer Alasdair Ivens Laura J. V. Piddock
author_facet	Michelle M. C. Buckner Jessica M. A. Blair Roberto M. La Ragione Jane Newcombe Daniel J. Dwyer Alasdair Ivens Laura J. V. Piddock
author_sort	Michelle M. C. Buckner
title	Beyond Antimicrobial Resistance: Evidence for a Distinct Role of the AcrD Efflux Pump in <italic toggle="yes">Salmonella</italic> Biology
title_short	Beyond Antimicrobial Resistance: Evidence for a Distinct Role of the AcrD Efflux Pump in <italic toggle="yes">Salmonella</italic> Biology
title_full	Beyond Antimicrobial Resistance: Evidence for a Distinct Role of the AcrD Efflux Pump in <italic toggle="yes">Salmonella</italic> Biology
title_fullStr	Beyond Antimicrobial Resistance: Evidence for a Distinct Role of the AcrD Efflux Pump in <italic toggle="yes">Salmonella</italic> Biology
title_full_unstemmed	Beyond Antimicrobial Resistance: Evidence for a Distinct Role of the AcrD Efflux Pump in <italic toggle="yes">Salmonella</italic> Biology
title_sort	beyond antimicrobial resistance: evidence for a distinct role of the acrd efflux pump in <italic toggle="yes">salmonella</italic> biology
publisher	American Society for Microbiology
publishDate	2016
url	https://doaj.org/article/c418bdbe44684db7a3104372910a266e
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Beyond Antimicrobial Resistance: Evidence for a Distinct Role of the AcrD Efflux Pump in <italic toggle="yes">Salmonella</italic> Biology

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