title: Triclosan can select for an AdeIJK-overexpressing mutant of Acinetobacter baumannii ATCC 17978 that displays reduced susceptibility to multiple antibiotics.
abstract: In order to determine if triclosan can select for mutants of Acinetobacter baumannii ATCC 17978 that display reduced susceptibilities to antibiotics, we isolated a triclosan-resistant mutant, A. baumannii AB042, by serial passaging of A. baumannii ATCC 17978 in growth medium supplemented with triclosan. The antimicrobial susceptibility of AB042 was analyzed by the 2-fold serial dilution method. Expression of five different resistance-nodulation-division (RND) pump-encoding genes (adeB, adeG, adeJ, A1S_2818, and A1S_3217), two outer membrane porin-encoding genes (carO and oprD), and the MATE family pump-encoding gene abeM was analyzed using quantitative reverse transcriptase (qRT) PCR. A. baumannii AB042 exhibited elevated resistance to multiple antibiotics, including piperacillin-tazobactam, doxycycline, moxifloxacin, ceftriaxone, cefepime, meropenem, doripenem, ertapenem, ciprofloxacin, aztreonam, tigecycline, and trimethoprim-sulfamethoxazole, in addition to triclosan. Genome sequencing of A. baumannii AB042 revealed a (116)G→V mutation in fabI, the gene encoding the target enzyme for triclosan. Expression analysis of efflux pumps showed overexpression of the AdeIJK pump, and sequencing of adeN, the gene that encodes the repressor of the adeIJK operon, revealed a 73-bp deletion which would cause a premature termination of translation, resulting in an inactive truncated AdeN protein. This work shows that triclosan can select for mutants of A. baumannii that display reduced susceptibilities to multiple antibiotics from chemically distinct classes in addition to triclosan resistance. This multidrug resistance can be explained by the overexpression of the AdeIJK efflux pump.
authors.affiliation: Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Dinesh M
authors.initials: DM
authors.lastname: Fernando
authors.affiliation: College of Pharmacy, University of Manitoba, Winnipeg, Manitoba, Canada Manitoba Institute of Child Health, Winnipeg, Manitoba, Canada.
authors.forename: Wayne
authors.initials: W
authors.lastname: Xu
authors.affiliation: Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Loewen
authors.affiliation: Department of Medical Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: George G
authors.initials: GG
authors.lastname: Zhanel
authors.affiliation: Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada Department of Medical Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada ayush.kumar@umanitoba.ca.
authors.forename: Ayush
authors.initials: A
authors.lastname: Kumar
mesh_terms: D000151:Acinetobacter Infections / Q000188:drug therapy / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D001483:Base Sequence; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D050753:Enoyl-(Acyl-Carrier-Protein) Reductase (NADH) / Q000235:genetics; D054889:Fatty Acid Synthase, Type II / Q000235:genetics; D054872:Fatty Acid Synthesis Inhibitors / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D016680:Genome, Bacterial / Q000235:genetics; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D012641:Selection, Genetic / Q000187:drug effects* / Q000235:genetics; D017422:Sequence Analysis, DNA; D014260:Triclosan / Q000494:pharmacology*
chemical_list: C445684:AdeB protein, Acinetobacter baumannii; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D054872:Fatty Acid Synthesis Inhibitors; D026901:Membrane Transport Proteins; D014260:Triclosan; D050753:Enoyl-(Acyl-Carrier-Protein) Reductase (NADH); D054889:Fatty Acid Synthase, Type II