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RamAp, an efflux pump regulator carried by an IncHI2 plasmid. Antimicrob Agents Chemother 2021; 66:e0115221. [PMID: 34694885 DOI: 10.1128/aac.01152-21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
In investigating the epidemiological trends of Salmonella enterica serovar Goldcoast, we have previously identified several closely related strains with different MICs to azithromycin and quinolones. Genome sequencing and comparison of two very similar MDR strains, R18.0877 and R18.1656, has led to the identification of an extra plasmid-borne ramA gene, ramAp, on the large IncHI2 plasmid carried by R18.0877. The ramAp is located in a 953-bp region on the plasmid, which is identical to that of the Klebsiella quasipneumoniae chromosomal ramA loci. A truncated ISEcp1 located at the adjacent upstream of the putative regulatory region of the ramAp may likely contribute to its mobilization and expression. Introducing the ramAp and the truncated ISEcp1 into E. coli have resulted in elevated expression of efflux pump genes and elevated MICs to chloramphenicol, azithromycin, nalidixic acid, ciprofloxacin, sulfamethoxazole, trimethoprim, tetracycline, and tigecycline. The ramAp is an extra efflux pump activator gene that potentially could be transmitted with the IncHI2 plasmid among bacteria. It is plausible that, with high interspecific conservation, the plasmid-encoded regulator reduces drug susceptibility by activating existing efflux pump systems of the host and thus can be regarded as a new type of auxiliary antimicrobial resistance determinant. Sequences of similar plasmids were found worldwide. Its impact on the emergence of antimicrobial resistance among bacterial pathogens is worrisome.
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Abstract
The transport of small molecules across membranes is essential for the import of nutrients and other energy sources into the cell and, for the export of waste and other potentially harmful byproducts out of the cell. While hydrophobic molecules are permeable to membranes, ions and other small polar molecules require transport via specialized membrane transport proteins . The two major classes of membrane transport proteins are transporters and channels. With our focus here on porins-major class of non-specific diffusion channel proteins , we will highlight some recent structural biology reports and functional assays that have substantially contributed to our understanding of the mechanism that mediates uptake of small molecules, including antibiotics, across the outer membrane of Enterobacteriaceae . We will also review advances in the regulation of porin expression and porin biogenesis and discuss these pathways as new therapeutic targets.
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Affiliation(s)
- Muriel Masi
- UMR_MD1, Inserm U1261, IRBA, Membranes et Cibles Thérapeutiques, Facultés de Médecine et de Pharmacie, Aix-Marseille Université, Marseille, France
| | | | - Jean-Marie Pagès
- UMR_MD1, Inserm U1261, IRBA, Membranes et Cibles Thérapeutiques, Facultés de Médecine et de Pharmacie, Aix-Marseille Université, Marseille, France.
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Fàbrega A, Ballesté-Delpierre C, Vila J. Differential impact of ramRA mutations on both ramA transcription and decreased antimicrobial susceptibility in Salmonella Typhimurium. J Antimicrob Chemother 2015; 71:617-24. [PMID: 26679248 DOI: 10.1093/jac/dkv410] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 11/03/2015] [Indexed: 11/14/2022] Open
Abstract
OBJECTIVES This study was focused on analysing the heterogeneity of mutations occurring in the regulators of efflux-mediated MDR in Salmonella Typhimurium. Moreover, the impact of such mutations on impairing the transcription of ramA, acrB, tolC and acrF was also assessed as was the impact on the resistance or decreased susceptibility phenotype. METHODS Strains were selected in vitro under increasing ciprofloxacin concentrations. Etest and broth microdilution tests were used to determine the MICs of several unrelated compounds. Screening of mutations in the quinolone target genes and MDR regulators was performed. RT-PCR analysis was used to detect the levels of expression of acrB, tolC, ompF, acrF, emrB, acrR, ramA, soxS and marA. RESULTS All mutant strains showed increased MICs of most of the antimicrobials tested, with the exception of kanamycin. Mutations in the quinolone target genes did not occur in all the mutants, which all harboured mutations in the ramRA regulatory region. All the mutants overexpressed ramA, tolC and acrB (only tested in 60-wt derivatives), whereas differential results were seen for the remaining genes. CONCLUSIONS Mutations in the ramRA region related to resistance and/or decreased susceptibility to antimicrobials predominate in Salmonella. There is heterogeneity in the types of mutations, with deletions affecting RamR-binding sites having a greater impact on ramA expression and the MDR phenotype.
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Affiliation(s)
- Anna Fàbrega
- ISGlobal, Barcelona Ctr. Int. Health Res. (CRESIB), Hospital Clínic-Universitat de Barcelona, Barcelona, Spain
| | - Clara Ballesté-Delpierre
- ISGlobal, Barcelona Ctr. Int. Health Res. (CRESIB), Hospital Clínic-Universitat de Barcelona, Barcelona, Spain
| | - Jordi Vila
- ISGlobal, Barcelona Ctr. Int. Health Res. (CRESIB), Hospital Clínic-Universitat de Barcelona, Barcelona, Spain Department of Clinical Microbiology, Hospital Clínic, School of Medicine, University of Barcelona, Barcelona, Spain
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De Majumdar S, Yu J, Fookes M, McAteer SP, Llobet E, Finn S, Spence S, Monaghan A, Kissenpfennig A, Ingram RJ, Bengoechea J, Gally DL, Fanning S, Elborn JS, Schneiders T. Elucidation of the RamA regulon in Klebsiella pneumoniae reveals a role in LPS regulation. PLoS Pathog 2015; 11:e1004627. [PMID: 25633080 PMCID: PMC4310594 DOI: 10.1371/journal.ppat.1004627] [Citation(s) in RCA: 84] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Accepted: 12/14/2014] [Indexed: 11/19/2022] Open
Abstract
Klebsiella pneumoniae is a significant human pathogen, in part due to high rates of multidrug resistance. RamA is an intrinsic regulator in K. pneumoniae established to be important for the bacterial response to antimicrobial challenge; however, little is known about its possible wider regulatory role in this organism during infection. In this work, we demonstrate that RamA is a global transcriptional regulator that significantly perturbs the transcriptional landscape of K. pneumoniae, resulting in altered microbe-drug or microbe-host response. This is largely due to the direct regulation of 68 genes associated with a myriad of cellular functions. Importantly, RamA directly binds and activates the lpxC, lpxL-2 and lpxO genes associated with lipid A biosynthesis, thus resulting in modifications within the lipid A moiety of the lipopolysaccharide. RamA-mediated alterations decrease susceptibility to colistin E, polymyxin B and human cationic antimicrobial peptide LL-37. Increased RamA levels reduce K. pneumoniae adhesion and uptake into macrophages, which is supported by in vivo infection studies, that demonstrate increased systemic dissemination of ramA overexpressing K. pneumoniae. These data establish that RamA-mediated regulation directly perturbs microbial surface properties, including lipid A biosynthesis, which facilitate evasion from the innate host response. This highlights RamA as a global regulator that confers pathoadaptive phenotypes with implications for our understanding of the pathogenesis of Enterobacter, Salmonella and Citrobacter spp. that express orthologous RamA proteins. Bacteria can rapidly evolve under antibiotic pressure to develop resistance, which occurs when target genes mutate, or when resistance-encoding genes are transferred. Alternatively, microbes can simply alter the levels of intrinsic proteins that allow the organism to “buy” time to resist antibiotic pressure. Klebsiella pneumoniae is a pathogen that causes significant blood stream or respiratory infections, but more importantly is a bacterium that is increasingly being reported as multidrug resistant. Our data demonstrate that RamA can trigger changes on the bacterial surface that allow Klebsiella to survive both antibiotic challenge, degradation by host immune peptides and resist phagocytosis. We demonstrate that the molecular basis of increased survival of ramA overexpressing K. pneumoniae, against host-derived factors is associated with RamA-driven alterations of the lipid A moiety of Klebsiella LPS. This modification is likely to be linked to Klebsiella’s ability to resist the host response so that it remains undetected by the immune system. The relevance of our work extends beyond RamA in Klebsiella as other pathogens such as Enterobacter spp and Salmonella spp. also produce this protein. Thus our overarching conclusion is that the intrinsic regulator, RamA perturbs host-microbe and microbe-drug interactions.
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Affiliation(s)
- Shyamasree De Majumdar
- Centre for Infection and Immunity, Belfast, United Kingdom
- Division of Pathway and Infection Medicine, Edinburgh, United Kingdom
| | - Jing Yu
- Centre for Infection and Immunity, Belfast, United Kingdom
| | - Maria Fookes
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Sean P. McAteer
- Division of Immunity and Infection, The Roslin Institute and R(D)SVS, The University of Edinburgh, Easter Bush, Midlothian, United Kingdom
| | - Enrique Llobet
- Laboratory Microbial Pathogenesis, Fundació d’Investigació Sanitària de les Illes Balears (FISIB) Recinto Hospital Joan March, Bunyola, Spain
| | - Sarah Finn
- UCD Centre for Molecular Innovation and Drug Discovery, School of Public Health, Physiotherapy & Population Science, University College Dublin, Dublin, Ireland
| | - Shaun Spence
- Centre for Infection and Immunity, Belfast, United Kingdom
| | - Avril Monaghan
- Centre for Infection and Immunity, Belfast, United Kingdom
| | | | | | - José Bengoechea
- Centre for Infection and Immunity, Belfast, United Kingdom
- Laboratory Microbial Pathogenesis, Fundació d’Investigació Sanitària de les Illes Balears (FISIB) Recinto Hospital Joan March, Bunyola, Spain
| | - David L. Gally
- Division of Immunity and Infection, The Roslin Institute and R(D)SVS, The University of Edinburgh, Easter Bush, Midlothian, United Kingdom
| | - Séamus Fanning
- UCD Centre for Molecular Innovation and Drug Discovery, School of Public Health, Physiotherapy & Population Science, University College Dublin, Dublin, Ireland
| | | | - Thamarai Schneiders
- Centre for Infection and Immunity, Belfast, United Kingdom
- Division of Pathway and Infection Medicine, Edinburgh, United Kingdom
- * E-mail:
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Adaptive and mutational resistance: role of porins and efflux pumps in drug resistance. Clin Microbiol Rev 2013; 25:661-81. [PMID: 23034325 DOI: 10.1128/cmr.00043-12] [Citation(s) in RCA: 528] [Impact Index Per Article: 48.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The substantial use of antibiotics in the clinic, combined with a dearth of new antibiotic classes, has led to a gradual increase in the resistance of bacterial pathogens to these compounds. Among the various mechanisms by which bacteria endure the action of antibiotics, those affecting influx and efflux are of particular importance, as they limit the interaction of the drug with its intracellular targets and, consequently, its deleterious effects on the cell. This review evaluates the impact of porins and efflux pumps on two major types of resistance, namely, mutational and adaptive types of resistance, both of which are regarded as key phenomena in the global rise of antibiotic resistance among pathogenic microorganisms. In particular, we explain how adaptive and mutational events can dramatically influence the outcome of antibiotic therapy by altering the mechanisms of influx and efflux of antibiotics. The identification of porins and pumps as major resistance markers has opened new possibilities for the development of novel therapeutic strategies directed specifically against these mechanisms.
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Akiyama T, Khan AA. Molecular characterization of strains of fluoroquinolone-resistant Salmonella enterica serovar Schwarzengrund carrying multidrug resistance isolated from imported foods. J Antimicrob Chemother 2011; 67:101-10. [DOI: 10.1093/jac/dkr414] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Zheng J, Tian F, Cui S, Song J, Zhao S, Brown EW, Meng J. Differential gene expression by RamA in ciprofloxacin-resistant Salmonella Typhimurium. PLoS One 2011; 6:e22161. [PMID: 21811569 PMCID: PMC3139621 DOI: 10.1371/journal.pone.0022161] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Accepted: 06/16/2011] [Indexed: 11/22/2022] Open
Abstract
Overexpression of ramA has been implicated in resistance to multiple drugs in several enterobacterial pathogens. In the present study, Salmonella Typhimurium strain LTL with constitutive expression of ramA was compared to its ramA-deletion mutant by employing both DNA microarrays and phenotype microarrays (PM). The mutant strain with the disruption of ramA showed differential expression of at least 33 genes involved in 11 functional groups. The study confirmed at the transcriptional level that the constitutive expression of ramA was directly associated with increased expression of multidrug efflux pump AcrAB-TolC and decreased expression of porin protein OmpF, thereby conferring multiple drug resistance phenotype. Compared to the parent strain constitutively expressing ramA, the ramA mutant had increased susceptibility to over 70 antimicrobials and toxic compounds. The PM analysis also uncovered that the ramA mutant was better in utilization of 10 carbon sources and 5 phosphorus sources. This study suggested that the constitutive expression of ramA locus regulate not only multidrug efflux pump and accessory genes but also genes involved in carbon metabolic pathways.
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Affiliation(s)
- Jie Zheng
- Joint Institute for Food Safety and Applied Nutrition, and Department of Nutrition and Food Science, University of Maryland, College Park, Maryland, United States of America
- Center for Food Safety & Applied Nutrition, U.S. Food & Drug Administration, Maryland, University of Maryland, College Park, Maryland, United States of America
| | - Fei Tian
- Department of Animal and Avian Science, University of Maryland, College Park, Maryland, United States of America
| | - Shenghui Cui
- State Food and Drug Administration, Beijing, China
| | - Jiuzhou Song
- Department of Animal and Avian Science, University of Maryland, College Park, Maryland, United States of America
| | - Shaohua Zhao
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Maryland, University of Maryland, College Park, Maryland, United States of America
| | - Eric W. Brown
- Center for Food Safety & Applied Nutrition, U.S. Food & Drug Administration, Maryland, University of Maryland, College Park, Maryland, United States of America
| | - Jianghong Meng
- Joint Institute for Food Safety and Applied Nutrition, and Department of Nutrition and Food Science, University of Maryland, College Park, Maryland, United States of America
- * E-mail:
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Amaral L, Fanning S, Pagès JM. Efflux pumps of gram-negative bacteria: genetic responses to stress and the modulation of their activity by pH, inhibitors, and phenothiazines. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2011; 77:61-108. [PMID: 21692367 DOI: 10.1002/9780470920541.ch2] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
Affiliation(s)
- Leonard Amaral
- Unit of Mycobacteriology, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Lisbon, Portugal
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Chinni SV, Raabe CA, Zakaria R, Randau G, Hoe CH, Zemann A, Brosius J, Tang TH, Rozhdestvensky TS. Experimental identification and characterization of 97 novel npcRNA candidates in Salmonella enterica serovar Typhi. Nucleic Acids Res 2010; 38:5893-908. [PMID: 20460466 PMCID: PMC2943607 DOI: 10.1093/nar/gkq281] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We experimentally identified and characterized 97 novel, non-protein-coding RNA candidates (npcRNAs) from the human pathogen Salmonella enterica serovar Typhi (hereafter referred to as S. typhi). Three were specific to S. typhi, 22 were restricted to Salmonella species and 33 were differentially expressed during S. typhi growth. We also identified Salmonella Pathogenicity Island-derived npcRNAs that might be involved in regulatory mechanisms of virulence, antibiotic resistance and pathogenic specificity of S. typhi. An in-depth characterization of S. typhi StyR-3 npcRNA showed that it specifically interacts with RamR, the transcriptional repressor of the ramA gene, which is involved in the multidrug resistance (MDR) of Salmonella. StyR-3 interfered with RamR–DNA binding activity and thus potentially plays a role in regulating ramA gene expression, resulting in the MDR phenotype. Our study also revealed a large number of cis-encoded antisense npcRNA candidates, supporting previous observations of global sense–antisense regulatory networks in bacteria. Finally, at least six of the npcRNA candidates interacted with the S. typhi Hfq protein, supporting an important role of Hfq in npcRNA networks. This study points to novel functional npcRNA candidates potentially involved in various regulatory roles including the pathogenicity of S. typhi.
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Affiliation(s)
- Suresh V Chinni
- Institute of Experimental Pathology (ZMBE), University of Muenster, Von-Esmarch-Str. 56, 48149 Muenster, Germany
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Koskenkorva-Frank TS, Kallio PT. Induction of Pseudomonas aeruginosa fhp and fhpR by reactive oxygen species. Can J Microbiol 2009; 55:657-63. [PMID: 19767835 DOI: 10.1139/w09-024] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In Pseudomonas aeruginosa, flavohemoglobin (Fhp) and its cognate regulator FhpR (PA2665) form a protective regulatory circuit, which responds to reactive nitrogen species and is also capable of protecting cells against nitrosative stress. Recently, it has been shown that the expression of the fhp promoter is regulated not only by FhpR, but also by two new regulators, PA0779 and PA3697. It has also been suggested that the bacterial flavohemoglobins (flavoHbs) could play a crucial role in the protection of cells against reactive oxygen species (ROS). Therefore, the role and function of the Fhp/FhpR system during oxidative stress were studied by assessing the viability and membrane integrity of P. aeruginosa cells and by analyzing the promoter activities of fhp and fhpR upon exposure to paraquat, hydrogen peroxide, and tert-butyl hydroperoxide, under both aerobic and low-oxygen conditions. The results showed that under aerobic conditions, both fhp and fhpR promoters are induced by ROS generated by the stressors. Thus, the Fhp/FhpR system is implicated in the oxidative stress response. ROS-induced fhp promoter activity was dependent on FhpR, PA0779, and PA3697 regulators. Tert-butyl hydroperoxide-induced fhpR promoter activity was found to be highly repressed by PA0779, and FhpR showed negative autoregulation of its own promoter. Under low-oxygen conditions, the activity of the fhp promoter was not inducible by ROS, but fhpR promoter activity was induced by paraquat, and hydrogen peroxide was repressed in both cases by the regulators PA0779 and PA3697.
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Abstract
Drug efflux pumps play a key role in drug resistance and also serve other functions in bacteria. There has been a growing list of multidrug and drug-specific efflux pumps characterized from bacteria of human, animal, plant and environmental origins. These pumps are mostly encoded on the chromosome, although they can also be plasmid-encoded. A previous article in this journal provided a comprehensive review regarding efflux-mediated drug resistance in bacteria. In the past 5 years, significant progress has been achieved in further understanding of drug resistance-related efflux transporters and this review focuses on the latest studies in this field since 2003. This has been demonstrated in multiple aspects that include but are not limited to: further molecular and biochemical characterization of the known drug efflux pumps and identification of novel drug efflux pumps; structural elucidation of the transport mechanisms of drug transporters; regulatory mechanisms of drug efflux pumps; determining the role of the drug efflux pumps in other functions such as stress responses, virulence and cell communication; and development of efflux pump inhibitors. Overall, the multifaceted implications of drug efflux transporters warrant novel strategies to combat multidrug resistance in bacteria.
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Affiliation(s)
- Xian-Zhi Li
- Human Safety Division, Veterinary Drugs Directorate, Health Products and Food Branch, Health Canada, Ottawa, Ontario K1A OK9, Canada
| | - Hiroshi Nikaido
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202, USA
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Nishino K, Nikaido E, Yamaguchi A. Regulation and physiological function of multidrug efflux pumps in Escherichia coli and Salmonella. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1794:834-43. [DOI: 10.1016/j.bbapap.2009.02.002] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2008] [Revised: 02/02/2009] [Accepted: 02/05/2009] [Indexed: 01/30/2023]
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Ricci V, Piddock LJV. Ciprofloxacin selects for multidrug resistance in Salmonella enterica serovar Typhimurium mediated by at least two different pathways. J Antimicrob Chemother 2009; 63:909-16. [PMID: 19270312 DOI: 10.1093/jac/dkp054] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVES The aim of this study was to understand the role of ramA in conferring multidrug resistance (MDR) in Salmonella enterica serovar Typhimurium. METHODS Two phenotypically distinct isogenic MDR laboratory mutants derived from Salmonella Typhimurium SL1344 and three human clinical isolates from a patient that failed antibiotic therapy, including with ciprofloxacin, were investigated for the cause of MDR. MICs were determined by agar dilution and efflux activity assessed by monitoring the accumulation of Hoechst 33342. The combination of specific genes and MDR was assessed by inactivation, and complementation RT-PCR was used to assess gene expression and DNA sequencing to identify mutations within genes of interest. RESULTS Mutation in ramR and the consequent over-production of ramA and acrB were revealed in one laboratory mutant selected with ciprofloxacin and this was associated with cyclohexane tolerance. Complementation of SL1344 ramR::aph with pUC19 ramR(mutant) conferred MDR and cyclohexane tolerance. However, analysis of a second ciprofloxacin-selected MDR mutant, which was susceptible to cyclohexane, revealed no mutation in ramR or altered expression of marA, soxS or rob. There was a mutation in ramR in both the pre- and post-therapy clinical isolates and no difference between the isolates in the level of expression of ramA. CONCLUSIONS These data show that ciprofloxacin exposure can select for mutations within ramR and consequently mediate MDR. These data also indicate that there is at least one further unidentified gene in addition to marA, soxS, rob and ramA that confers MDR in S. enterica.
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Feuerriegel S, Heisig P. Role of Global Regulator Rma for Multidrug Efflux–Mediated Fluoroquinolone Resistance inSalmonella. Microb Drug Resist 2008; 14:259-63. [DOI: 10.1089/mdr.2008.0846] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Silke Feuerriegel
- Pharmaceutical Biology and Microbiology, University of Hamburg, Bundesstrasse, Hamburg, Germany
| | - Peter Heisig
- Pharmaceutical Biology and Microbiology, University of Hamburg, Bundesstrasse, Hamburg, Germany
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Zheng J, Cui S, Meng J. Effect of transcriptional activators RamA and SoxS on expression of multidrug efflux pumps AcrAB and AcrEF in fluoroquinolone-resistant Salmonella Typhimurium. J Antimicrob Chemother 2008; 63:95-102. [DOI: 10.1093/jac/dkn448] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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RamA confers multidrug resistance in Salmonella enterica via increased expression of acrB, which is inhibited by chlorpromazine. Antimicrob Agents Chemother 2008; 52:3604-11. [PMID: 18694955 DOI: 10.1128/aac.00661-08] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
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.
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Nikaido E, Yamaguchi A, Nishino K. AcrAB multidrug efflux pump regulation in Salmonella enterica serovar Typhimurium by RamA in response to environmental signals. J Biol Chem 2008; 283:24245-53. [PMID: 18577510 PMCID: PMC2527123 DOI: 10.1074/jbc.m804544200] [Citation(s) in RCA: 158] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
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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Affiliation(s)
- Eiji Nikaido
- Department of Cell Membrane Biology, Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan
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ramR mutations involved in efflux-mediated multidrug resistance in Salmonella enterica serovar Typhimurium. Antimicrob Agents Chemother 2008; 52:2428-34. [PMID: 18443112 DOI: 10.1128/aac.00084-08] [Citation(s) in RCA: 128] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the sequenced genome of Salmonella enterica serovar Typhimurium strain LT2, an open reading frame (STM0580) coding for a putative regulatory protein of the TetR family is found upstream of the ramA gene. Overexpression of ramA results in increased expression of the AcrAB efflux pump and, consequently, multidrug resistance (MDR) in several bacterial species. The inactivation of the putative regulatory protein gene upstream of ramA in a susceptible serovar Typhimurium strain resulted in an MDR phenotype with fourfold increases in the MICs of unrelated antibiotics, such as quinolones/fluoroquinolones, phenicols, and tetracycline. The inactivation of this gene also resulted in a fourfold increase in the expression of ramA and a fourfold increase in the expression of the AcrAB efflux pump. These results indicated that the gene encodes a local repressor of ramA and was thus named ramR. In contrast, the inactivation of marR, marA, soxR, and soxS did not affect the susceptibilities of the strain. In quinolone- or fluoroquinolone-resistant strains of serovar Typhimurium overexpressing AcrAB, several point mutations which resulted in amino acid changes or an in-frame shift were identified in ramR; in addition, mutations interrupting ramR with an IS1 element were identified in high-level fluoroquinolone-resistant serovar Typhimurium DT204 strains. One serovar Typhimurium DT104 isolate had a 2-nucleotide deletion in the putative RamR binding site found upstream of ramA. These mutations were confirmed to play a role in the MDR phenotype by complementing the isolates with an intact ramR gene or by inactivating their respective ramA gene. No mutations in the mar or sox region were found in the strains studied. In conclusion, mutations in ramR appear to play a major role in the upregulation of RamA and AcrAB and, consequently, in the efflux-mediated MDR phenotype of serovar Typhimurium.
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Hernández-Urzúa E, Zamorano-Sánchez DS, Ponce-Coria J, Morett E, Grogan S, Poole RK, Membrillo-Hernández J. Multiple regulators of the Flavohaemoglobin (hmp) gene of Salmonella enterica serovar Typhimurium include RamA, a transcriptional regulator conferring the multidrug resistance phenotype. Arch Microbiol 2006; 187:67-77. [PMID: 17024490 DOI: 10.1007/s00203-006-0175-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2006] [Revised: 07/20/2006] [Accepted: 08/30/2006] [Indexed: 11/28/2022]
Abstract
Microbial flavohaemoglobins are proteins with homology to haemoglobins from higher organisms, but clearly linked to nitric oxide (NO) metabolism by bacteria and yeast. hmp mutant strains of several bacteria are hypersensitive to NO and related compounds and hmp genes are up-regulated by the presence of NO. The regulatory mechanisms involved in hmp induction by NO and the superoxide-generating agent, methyl viologen (paraquat; PQ), are complex, but progressively being resolved. Here we show for the first time that, in Salmonella enterica serovar Typhimurium, hmp transcription is increased on exposure to PQ and demonstrate that RamA, a homologue of MarA is responsible for most of the hmp paraquat regulation. In addition we demonstrate NO-dependent elevation of Salmonella hmp transcription and Hmp accumulation. In both Escherichia coli and Salmonella modest transcriptional repression of hmp is exerted by the iron responsive transcriptional repressor Fur. Finally, in contrast to previous reports, we show that in E. coli and Salmonella, hmp induction by both paraquat and sodium nitroprusside is further elevated in a fur mutant background, indicating that additional regulators are implicated in this control process.
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Affiliation(s)
- Elizabeth Hernández-Urzúa
- Laboratorio de Microbiología y Genética Molecular, Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, PO Box 70-228, Coyoacán, Mexico City 04510, Mexico
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20
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Giraud E, Baucheron S, Cloeckaert A. Resistance to fluoroquinolones in Salmonella: emerging mechanisms and resistance prevention strategies. Microbes Infect 2006; 8:1937-44. [PMID: 16714137 DOI: 10.1016/j.micinf.2005.12.025] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2005] [Accepted: 12/28/2005] [Indexed: 11/18/2022]
Abstract
We review the current state of knowledge about the genetic and biochemical mechanisms that mediate quinolone resistance in Salmonella. They include modifications of topoisomerase targets, increased efflux activity and the recently described topoisomerase protection by the plasmid-encoded Qnr protein. We discuss what factors may determine the order of implementation of these various mechanisms in a particular strain, and what strategies could be used to combat resistance, from the inhibition of mutagenesis mechanisms to counteracting, during fluoroquinolone treatment, of resistance mechanisms already set in the infecting strain.
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Affiliation(s)
- Etienne Giraud
- UMR INRA-ENVN Chimiothérapie Aquacole et Environnement, La Chantrerie, BP 40706, 44307 Nantes Cedex 03, France.
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21
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McDonald R, Burnett V. Novel single-round PCR and cloning of full-length envelope genes of HIV-1 may yield new insight into biomolecular antibacterial drug development. J Virol Methods 2005; 126:111-8. [PMID: 15847926 DOI: 10.1016/j.jviromet.2005.01.027] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2004] [Revised: 01/17/2005] [Accepted: 01/18/2005] [Indexed: 11/20/2022]
Abstract
Nested or semi-nested polymerase chain reaction (PCR) with a 'hot start' is the preferred amplification method for full-length, in-frame envelope genes (gp160) of the human immunodeficiency virus type 1 (HIV-1). This generally follows an extensive screening process. This paper describes an effective single-round PCR method and cloning process for HIV-1 gp160 from clinical samples, and cell and tissue cultures developed during the early stages of construction of a molecular HIV-1 vaccine. The amplification method and cloning process are adaptable to full-length HIV-1, HIV-2, and other viral production processes. Also described within, is one solution to the most-often extensive screening process for inserts containing full-length, in-frame gp160. Of note, was a perceived toxicity of gp160 to bacteria during the culturing and the scaling-up process that created the extensive screening process. The toxicity association was not found with the individual gp160 genes, the gp120 or the gp41 gene, with other viral regions similar or larger in molecular weight to gp160, or with other non-gp160 full-length genes of HIV-1 such as pol and gag genes. The HIV-1 gp160 toxicity issue may provide insight towards the development of the next generation of novel biomolecular drugs against bacterial infections.
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Affiliation(s)
- Richard McDonald
- Biomedical Health Sciences Division, Genovar Diagnostics, 1030 Heeley Close, Sittingbourne Research Centre, Sittingbourne ME9 8HL, Kent, UK.
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22
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Ruzin A, Visalli MA, Keeney D, Bradford PA. Influence of transcriptional activator RamA on expression of multidrug efflux pump AcrAB and tigecycline susceptibility in Klebsiella pneumoniae. Antimicrob Agents Chemother 2005; 49:1017-22. [PMID: 15728897 PMCID: PMC549240 DOI: 10.1128/aac.49.3.1017-1022.2005] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Tigecycline is an expanded broad-spectrum antibacterial agent that is active against many clinically relevant species of bacterial pathogens, including Klebsiella pneumoniae. The majority of K. pneumoniae isolates are fully susceptible to tigecycline; however, a few strains that have decreased susceptibility have been isolated. One isolate, G340 (for which the tigecycline MIC is 4 microg/ml and which displays a multidrug resistance [MDR] phenotype), was selected for analysis of the mechanism for this decreased susceptibility by use of transposon mutagenesis with IS903phikan. A tigecycline-susceptible mutant of G340, GC7535, was obtained (tigecycline MIC, 0.25 microg/ml). Analysis of the transposon insertion mapped it to ramA, a gene that was previously identified to be involved in MDR in K. pneumoniae. For GC7535, the disruption of ramA led to a 16-fold decrease in the MIC of tigecycline and also a suppression of MDR. Trans-complementation with plasmid-borne ramA restored the original parental phenotype of decreased susceptibility to tigecycline. Northern blot analysis revealed a constitutive overexpression of ramA that correlated with an increased expression of the AcrAB transporter in G340 compared to that in tigecycline-susceptible strains. Laboratory mutants of K. pneumoniae with decreased susceptibility to tigecycline could be selected at a frequency of approximately 4 x 10(-8). These results suggest that ramA is associated with decreased tigecycline susceptibility in K. pneumoniae due to its role in the expression of the AcrAB multidrug efflux pump.
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Affiliation(s)
- Alexey Ruzin
- Wyeth Research, Department of Infectious Disease, 401 North Middletown Rd., Bldg. 200, Rm. 3219, Pearl River, NY 10965, USA.
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Chollet R, Chevalier J, Bollet C, Pages JM, Davin-Regli A. RamA is an alternate activator of the multidrug resistance cascade in Enterobacter aerogenes. Antimicrob Agents Chemother 2004; 48:2518-23. [PMID: 15215103 PMCID: PMC434192 DOI: 10.1128/aac.48.7.2518-2523.2004] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Multidrug resistance (MDR) in Enterobacter aerogenes can be mediated by induction of MarA, which is triggered by certain antibiotics and phenolic compounds. In this study, we identified the gene encoding RamA, a 113-amino-acid regulatory protein belonging to the AraC-XylS transcriptional activator family, in the Enterobacter aerogenes ATCC 13048 type strain and in a clinical multiresistant isolate. Overexpression of RamA induced an MDR phenotype in drug-susceptible Escherichia coli JM109 and E. aerogenes ATCC 13048, as demonstrated by 2- to 16-fold-increased resistance to beta-lactams, tetracycline, chloramphenicol, and quinolones, a decrease in porin production, and increased production of AcrA, a component of the AcrAB-TolC drug efflux pump. We show that RamA enhances the transcription of the marRAB operon but is also able to induce an MDR phenotype in a mar-deleted strain. We demonstrate here that RamA is a transcriptional activator of the Mar regulon and is also a self-governing activator of the MDR cascade.
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Affiliation(s)
- Renaud Chollet
- Enveloppe Bactérienne, Perméabilité et Antibiotiques, EA 2197, IFR 48, Facultés de Médecine et Pharmacie, Université de la Méditerranée, 27 Boulevard Jean Moulin, 13385 Marseille Cedex 05, France
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van der Straaten T, Janssen R, Mevius DJ, van Dissel JT. Salmonella gene rma (ramA) and multiple-drug-resistant Salmonella enterica serovar typhimurium. Antimicrob Agents Chemother 2004; 48:2292-4. [PMID: 15155237 PMCID: PMC415616 DOI: 10.1128/aac.48.6.2292-2294.2004] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
MarA and its homologue, RamA, have been implicated in multidrug resistance (MDR). RamA overexpression in Salmonella enterica serovar Typhimurium and Escherichia coli conferred MDR independently of marA. Inactivation of ramA did not affect the antibiotic susceptibilities of wild-type S. enterica serovar Typhimurium or 15 unrelated clinical MDR isolates. Thus, ramA overexpression is not a common MDR mechanism in Salmonella.
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Affiliation(s)
- Tahar van der Straaten
- Department of Infectious Diseases, Leiden University Medical Center, P.O. Box 9600, 2300 RC Leiden, The Netherlands.
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25
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van der Straaten T, Zulianello L, van Diepen A, Granger DL, Janssen R, van Dissel JT. Salmonella enterica serovar Typhimurium RamA, intracellular oxidative stress response, and bacterial virulence. Infect Immun 2004; 72:996-1003. [PMID: 14742546 PMCID: PMC321585 DOI: 10.1128/iai.72.2.996-1003.2004] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Escherichia coli and Salmonella enterica serovar Typhimurium have evolved genetic systems, such as the soxR/S and marA regulons, to detoxify reactive oxygen species, like superoxide, which are formed as by-products of metabolism. Superoxide also serves as a microbicidal effector mechanism of the host's phagocytes. Here, we investigate whether regulatory genes other than soxR/S and marA are active in response to oxidative stress in Salmonella and may function as virulence determinants. We identified a bacterial gene, which was designated ramA (342 bp) and mapped at 13.1 min on the Salmonella chromosome, that, when overexpressed on a plasmid in E. coli or Salmonella, confers a pleiotropic phenotype characterized by increased resistance to the redox-cycling agent menadione and to multiple unrelated antibiotics. The ramA gene is present in Salmonella serovars but is absent in E. coli. The gene product displays 37 to 52% homology to the transcriptional activators soxR/S and marA and 80 to 100% identity to a multidrug resistance gene in Klebsiella pneumoniae and Salmonella enterica serovar Paratyphi A. Although a ramA soxR/S double null mutant is highly susceptible to intracellular superoxide generated by menadione and displays decreased Mn-superoxide dismutase activity, intracellular survival of this mutant within macrophage-like RAW 264.7 cells and in vivo replication in the spleens in Ityr mice are not affected. We concluded that despite its role in the protective response of the bacteria to oxidative stress in vitro, the newly identified ramA gene, together with soxR/S, does not play a role in initial replication of Salmonella in the organs of mice.
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Affiliation(s)
- Tahar van der Straaten
- Department of Infectious Diseases, Leiden University Medical Center, 2300 RC Leiden, The Netherlands
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Salipante SJ, Barlow M, Hall BG. GeneHunter, a transposon tool for identification and isolation of cryptic antibiotic resistance genes. Antimicrob Agents Chemother 2004; 47:3840-5. [PMID: 14638492 PMCID: PMC296228 DOI: 10.1128/aac.47.12.3840-3845.2003] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
GeneHunter is a transposon tool designed for the experimental activation and identification of silent antibiotic resistance genes. The method permits the identification of novel resistance genes that lack previously identified homologues. Using Salmonella enterica serovar Typhimurium strain LT2 as a test organism for the in vivo version of the GeneHunter method, we were able to activate, clone, and identify two cryptic antibiotic resistance genes, the aminoglycoside acetyltransferase aac(6')-Iaa and the probable Mar-A regulon activator rma. Because the method requires being able to electroporate the host with an efficiency of at least 10(10) transformants per microgram, the in vivo method is not applicable to most microorganisms. We therefore developed an in vitro transposition method, showed that it can also recover the cryptic rma gene from S. enterica serovar Typhimurium strain LT2, and showed that it is generally applicable to a variety of microorganisms by using it to recover a cryptic metallo-beta-lactamase gene from the gram-positive organism Bacillus cereus. It is anticipated that the GeneHunter method will be used to identify potential resistance genes during the development and testing of novel antibiotics, new variants of existing antibiotics, and drug inhibitor combinations.
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27
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Janssen R, van der Straaten T, van Diepen A, van Dissel JT. Responses to reactive oxygen intermediates and virulence of Salmonella typhimurium. Microbes Infect 2003; 5:527-34. [PMID: 12758282 DOI: 10.1016/s1286-4579(03)00069-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Salmonella typhimurium is an intracellular pathogen that can survive and replicate in macrophages. One of the host defense mechanisms that S. typhimurium encounters upon infection is superoxide produced by the phagocytes' NADPH-oxidase. Salmonella has evolved numerous ways of coping with superoxide in the extracellular environment. In addition, Salmonella has to defend itself against superoxide produced as a by-product of aerobic respiration. Over the last decade, research on bacterial mutants has led to the identification of Salmonella strains that differ from their parental strain in susceptibility to superoxide in vitro. However, the consequences of such mutations for bacterial virulence are highly variable, indicating that superoxide sensitivity per se is not a characteristic that renders Salmonella less virulent. By discussing various bacterial mutants classified according to their in vitro sensitivity to superoxide, we will exemplify the complex mechanisms that Salmonella has evolved to cope with superoxide stress.
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Affiliation(s)
- Riny Janssen
- Department of Infectious Diseases, C5-P, Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands.
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