The qacG gene on plasmid pST94 confers resistance to quaternary ammonium compounds in staphylococci isolated from the food industry.
The 2.3 kb resistance plasmid pST94 revealed a new gene (qacG) encoding resistance to benzalkonium chloride (BC), a commonly used quaternary ammonium disinfectant, and the intercalating dye ethidium bromide (Eb) in staphylococci isolated from the food industry. The 107 amino acid QacG protein showing 69.2% identity to the staphylococcal multi-drug resistance protein Smr is a new member of the small multi-drug resistance (SMR) protein family. QacG conferred resistance via proton dependent efflux. An additional ORF on pST94 encoded a protein with extensive similarity to replication proteins of other Gram-positive bacteria. Gene constructs containing the qacG and smr gene region combined with the smr or qacG promoter, respectively, indicated that QacG is more efficient than Smr and that qacG has a weaker promoter. Resistant qacG-containing cells could be adapted to withstand higher concentrations of BC. Adapted qacG-containing cells showed increased resistance mainly to BC. In contrast, adaptation of sensitive cells showed cross-resistance development to a range of compounds. Induction of proton-dependent efflux was observed for BC-adapted staphylococci cells not containing qacG. The ability of sublethal concentrations of BC to develop cross-resistance and induce efflux mechanisms could be of practical significance; it should be considered before use of any new disinfectant and in the design of better disinfection procedures.
Heir
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MATFORSK, Norwegian Food Research Institute, As, Norway. even.heir@folkehelsa.no
Sundheim
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Holck
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D000891:Anti-Infective Agents, Local / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology; D017920:Antiporters; D001483:Base Sequence; D001548:Benzalkonium Compounds / Q000494:pharmacology*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000031:analogs & derivatives / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics*; D017931:DNA Primers; D004269:DNA, Bacterial / Q000032:analysis / Q000302:isolation & purification; D004351:Drug Resistance / Q000235:genetics*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D029968:Escherichia coli Proteins; D004996:Ethidium / Q000494:pharmacology; D005516:Food Microbiology; D015964:Gene Expression Regulation, Bacterial; D007476:Ionophores / Q000494:pharmacology; D008565:Membrane Proteins / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009861:Onium Compounds / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000494:pharmacology; D010957:Plasmids; D011370:Proflavine / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D017386:Sequence Homology, Amino Acid; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development
D000891:Anti-Infective Agents, Local; D000970:Antineoplastic Agents; D017920:Antiporters; D001548:Benzalkonium Compounds; D002352:Carrier Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D007476:Ionophores; D008565:Membrane Proteins; D009861:Onium Compounds; D009943:Organophosphorus Compounds; C075436:EmrE protein, E coli; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D011370:Proflavine; D004996:Ethidium; C013289:tetraphenylphosphonium