The Vibrio cholerae var regulon encodes a metallo-β-lactamase and an antibiotic efflux pump, which are regulated by VarR, a LysR-type transcription factor

• Published in: PloS one Vol. 12; no. 9; p. e0184255
• Main Authors: Lin, Hong-Ting Victor, Massam-Wu, Teresa, Lin, Chen-Ping, Wang, Yen-Jen Anna, Shen, Yu-Chi, Lu, Wen-Jung, Hsu, Pang-Hung, Chen, Yu-Hou, Borges-Walmsley, Maria Ines, Walmsley, Adrian Robert
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.09.2017; Public Library of Science (PLoS)
• Subjects: Anti-Bacterial Agents - metabolism; Anti-Bacterial Agents - pharmacology; Antibiotic resistance; Antibiotics; Antimicrobial agents; ATP-Binding Cassette Transporters - genetics; ATP-Binding Cassette Transporters - metabolism; Bacteria; Base Sequence; beta-Lactamases - genetics; Biology and Life Sciences; Carbapenems; Cephalosporins; Cholera; Deoxyribonucleic acid; DNA; DNA, Intergenic; Drug resistance; Drug Resistance, Bacterial; Drugs; E coli; Efflux; Epidemics; Food contamination & poisoning; Food science; Gene expression; Gene Expression Regulation, Bacterial; Gene regulation; Genes; Genes, Bacterial; Genomes; Hydrolysis; Kinetics; Medicine and Health Sciences; Membrane Transport Proteins - genetics; Meropenem; Metallography; Microbial Sensitivity Tests; Nucleotide sequence; Pathogens; Penicillin; Promoter Regions, Genetic; Protein Binding; Regulation; Regulon; Research and Analysis Methods; Spiramycin; Transcription Factors - metabolism; Transcription, Genetic; Vibrio cholerae - drug effects; Vibrio cholerae - genetics; Vibrio cholerae - metabolism; Waterborne diseases; Brazil; Taiwan
• DOI: 10.1371/journal.pone.0184255
• ISSN: 1932-6203

The genome sequence of V. cholerae O1 Biovar Eltor strain N16961 has revealed a putative antibiotic resistance (var) regulon that is predicted to encode a transcriptional activator (VarR), which is divergently transcribed relative to the putative resistance genes for both a metallo-β-lactamase (VarG) and an antibiotic efflux-pump (VarABCDEF). We sought to test whether these genes could confer antibiotic resistance and are organised as a regulon under the control of VarR. VarG was overexpressed and purified and shown to have β-lactamase activity against penicillins, cephalosporins and carbapenems, having the highest activity against meropenem. The expression of VarABCDEF in the Escherichia coli (ΔacrAB) strain KAM3 conferred resistance to a range of drugs, but most significant resistance was to the macrolide spiramycin. A gel-shift analysis was used to determine if VarR bound to the promoter regions of the resistance genes. Consistent with the regulation of these resistance genes, VarR binds to three distinct intergenic regions, varRG, varGA and varBC located upstream and adjacent to varG, varA and varC, respectively. VarR can act as a repressor at the varRG promoter region; whilst this repression was relieved upon addition of β-lactams, these did not dissociate the VarR/varRG-DNA complex, indicating that the de-repression of varR by β-lactams is indirect. Considering that the genomic arrangement of VarR-VarG is strikingly similar to that of AmpR-AmpC system, it is possible that V. cholerae has evolved a system for resistance to the newer β-lactams that would prove more beneficial to the bacterium in light of current selective pressures.