title: Positive adaptive state: microarray evaluation of gene expression in Salmonella enterica Typhimurium exposed to nalidixic acid.
abstract: The emergence of antimicrobial resistance among foodborne bacteria associated with food animal production is an important global issue. We hypothesised that antibiotics generate a positive adaptive state in Salmonella that actively contributes to the development of antimicrobial resistance. This is opposed to common views that antimicrobials only act as a passive selective pressure. Microarray analysis was used to evaluate changes in gene expression that occur upon exposure of Salmonella enterica Typhimurium ATCC 14028 to 1.6 microg/mL of nalidixic acid. The results showed a significant (P < 0.02) difference (fold expression differences >2.0) in the expression of 226 genes. Comparatively repressed transcripts included Salmonella pathogenicity islands 1 and 2 (SPI1 and SPI2). Induced genes included efflux pumps representing all five families of multidrug-resistance efflux pumps, outer membrane lipoproteins, and genes involved in regulating lipopolysaccharide chain length. This profile suggests both enhanced antimicrobial export from the cell and membrane permeability adaptations to limit diffusion of nalidixic acid into the cell. Finally, increased expression of the error-prone DNA repair mechanisms were also observed. From these data we show a highly integrated genetic response to nalidixic acid that places Salmonella into a positive adaptive state that elicits mutations. Evaluation of gene expression profile changes that occur during exposure to antibiotics will continue to improve our understanding of the development of antibiotic resistance.
authors.affiliation: United States Department of Agriculture, Agricultural Research Service, Livestock Issues Research Unit, Lubbock, Texas 79403, USA. sdowd@lbk.usda.gov
authors.forename: Scot E
authors.initials: SE
authors.lastname: Dowd
authors.forename: Karen
authors.initials: K
authors.lastname: Killinger-Mann
authors.forename: John
authors.initials: J
authors.lastname: Blanton
authors.forename: Michael
authors.initials: M
authors.lastname: San Francisco
authors.forename: Mindy
authors.initials: M
authors.lastname: Brashears
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D005516:Food Microbiology; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D006801:Humans; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology*; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics / Q000378:metabolism
chemical_list: D000890:Anti-Infective Agents; D009268:Nalidixic Acid