title: Effects of Saline, an Ambient Acidic Environment, and Sodium Salicylate on OXA-Mediated Carbapenem Resistance in Acinetobacter baumannii.
abstract: Different physiological conditions, such as NaCl, low pH, and sodium salicylate, have been shown to affect antibiotic resistance determinants in Acinetobacter baumannii isolates. Therefore, the aim of this study was to investigate the effects of NaCl, sodium salicylate, and low pH on the susceptibility of A. baumannii to carbapenem. We cloned genes encoding oxacillinases (OXA) of different subclasses, with their associated promoters, from carbapenem-resistant A. baumannii isolates into the same vector and transferred them to the A. baumannii reference strains ATCC 19606 and ATCC 17978. Carbapenem MICs were determined at least in triplicate by agar dilution under standard conditions, as well as in the presence of 200 mM NaCl or 16 mM sodium salicylate, or at pH 5.8. OXA-58-like gene expression was determined by reverse transcription-quantitative PCR (qRT-PCR). Under some experimental conditions, significant MIC reductions were shown for some transformants but not for others. Only in one instance were all transformants harboring the same OXA affected by the same condition: at pH 5.8, the imipenem and meropenem MICs for strains expressing OXA-58-like enzymes decreased from a resistant level (32 to 64 mg/liter) to an intermediate-susceptible level (8 mg/liter). However, blaOXA-58-like gene expression remained the same. MICs for both wild-type reference strains were not affected by the conditions tested. Our results indicate that the effects of the experimental conditions tested on OXA in vivo are mostly strain dependent. MICs were not reduced to wild-type levels, suggesting that the conditions tested do not lead to complete OXA inhibition in the bacterial cell.
authors.affiliation: Institute for Medical Microbiology, Immunology, and Hygiene, University of Cologne, Cologne, Germany.
authors.forename: Esther
authors.initials: E
authors.lastname: Zander
authors.affiliation: Institute for Medical Microbiology, Immunology, and Hygiene, University of Cologne, Cologne, Germany German Center for Infection Research, Cologne-Bonn, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Seifert
authors.affiliation: Institute for Medical Microbiology, Immunology, and Hygiene, University of Cologne, Cologne, Germany paul.higgins@uni-koeln.de.
authors.forename: Paul G
authors.initials: PG
authors.lastname: Higgins
mesh_terms: D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015780:Carbapenems / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D008826:Microbial Sensitivity Tests; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride / Q000494:pharmacology*; D012980:Sodium Salicylate / Q000494:pharmacology*; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D015780:Carbapenems; D012965:Sodium Chloride; D001618:beta-Lactamases; C108449:oxacillinase; D012980:Sodium Salicylate