Association of doripenem resistance with OXA-type carbapenemases in Acinetobacter baumannii isolates

OBJECTIVES To evaluate the in vitro activity of doripenem in Acinetobacter baumannii (A. baumannii) clinical isolates that possess different OXA-type carbapenemases, and to evaluate the roles of these enzymes in the development of carbapenem resistance. METHODS This retrospective study was conducted with 25 A. baumannii isolates at Sakarya University Training and Research Hospital, Sakarya, Turkey from June to October 2014. Antibiotic susceptibility testing was carried out using the Vitek-2 automated system (bioMérieux, Marcy l'Etoile, France). Minimum inhibitory concentrations (MICs) were determined using Etest strips (bioMérieux, Marcy l'Etoile, France). Quantitative polymerase chain reaction was performed in a Fluorion Instrument (Iontek, Istanbul, Turkey).  RESULTS Isolates were divided into 5 groups based on their susceptibility profiles and OXA-type carbapenemase positivity. Group 2 isolates whose MIC of both meropenem and doripenem are in the range of 4-32 µg/mL were negative for both blaOXA-23 and blaOXA-58. Group 3 isolates whose MIC of meropenem and doripenem is in the range of 4-32 µg/mL, blaOXA-23 is positive, and blaOXA-58 is negative. Group 5 isolates whose MIC of meropenem is more than 32 µg/mL, and that of doripenem is in the range of 16-32 µg/mL were positive for both blaOXA-23 and blaOXA-58.  CONCLUSION The blaOXA-23 and blaOXA-58 gene combinations may confer resistance with a much greater MIC of both meropenem and doripenem. But the blaOXA-58 presence alone was not correlated with doripenem resistance.