Correlation of Oxacillinase Gene Carriage With the Genetic Fingerprints of Imipenem-Resistant Clinical Isolates of Acinetobacter baumannii

BACKGROUND: Emergence of multidrug-resistant Acinetobacter baumannii has resulted in the treatment failure of related infections and an increase in patient mortality. The presence of class D β-lactamases (oxacillinases) in this organism is an important mechanism underlying resistance to beta-lactam antibiotics. OBJECTIVES: The aim of this work was to investigate the correlation between oxacillinase gene carriage and genetic fingerprints in imipenem-resistant burn and non-burn isolates of A. baumannii. MATERIALS AND METHODS: Fifty-eight A. baumannii isolates were collected from October 2011 to April 2012, which included 28 burn isolates from Shahid Motahari Hospital and 30 non-burn isolates from Imam Hossein Hospital. The minimum inhibitory and minimum bactericidal concentrations (MIC and MBC) of imipenem were measured by the broth microdilution method. The presence of oxacillinase genes (OXA-23-, OXA-24-, OXA-51-, and OXA-58-like genes) was shown using type-specific primers and PCR. Genetic profiles were generated by RAPD-PCR fingerprinting. RESULTS: OXA-23 was observed in 81% of the isolates and its distribution was similar within the two groups. The presence of OXA-51 was shown in 58.6% of the isolates, of which most were burn isolates (67.6%). OXA-24 was present in 20.7% of the isolates, all belonging to the burn group; OXA-58 was not observed in any of the isolates. RAPD-PCR fingerprints revealed two clusters at a similarity level of 70% (A, B). At a similarity level of 85%, nine different groups were observed for burn and non-bun isolates. CONCLUSIONS: Our results showed that bla(OXA-23) was the most prevalent gene, followed by bla(OXA-51), among the burn and non-burn clinical isolates of A. baumannii. Bla(OXA-24)-like genes were detected at a lower level and were only found among the burn isolates, which also showed higher heterogeneity compared to the non-burn group.