Molecular Detection of Class-D OXA Carbapenemase Genes in Biofilm and Non-Biofilm Forming Clinical Isolates of Acinetobacter baumannii

Emergence and spread of carbapenemase (bla OXA) genes in multidrug resistant Acinetobacter baumannii (MDR-AB) forming biofilm complicated treatment of the patients infected with this microorganism particularly in intensive care units (ICUs). Objectives: The current study aimed to determine the prevalence of molecular class-D OXA carbapenemase in biofilm and non-biofilm forming strains of MDR-AB. Materials and

Coexistence of the bla OXA-51, bla OXA-23 and bla OXA-24/40 like genes, along with formation of strong biofilm, in MDR-AB strains particularly with indiscriminate use of imipenem, complicated treatment of the patients infected with these bacteria in the hospitals understudy.

A total of 65 strains of MDR-AB were isolated from the patients hospitalized in the ICU of two hospitals in Kerman, Iran. The isolates were identified by conventional microbiological tests as well as API 20NE assay. Antibiotic susceptibility was carried out by disk diffusion method; minimum inhibitory concentration (MIC) of carbapenems was measured by E-test. The presence of bla OXA genes among the isolates were studied by duplex-polymerase chain reaction and application of appropriate primers. Biofilm formation was detected by microtiter plate method.

The isolates were highly resistant to ciprofloxacin, levofloxacin, piperacillin, nalidixic acid and third generation cephalosporins such as tigecycline (7%; n = 5) and colistin (13%; n = 8). Among the isolates, 77% (n = 50) exhibited high MIC (265μg/mL) for imipenem. Both the bla OXA-51 and bla OXA-23 like genes coexisted in all the isolates; while, bla OXA-24/40 like gene was only detected in 29 imipenem-resistant strains (P ≤ 0.05). The bla OXA-58 like gene was not detected among the isolated strains. Quantification of biofilm introduced 23 isolates (including bla OXA-24/40 strains) with efficient attachment to microtiter plate; while, those isolates without bla OXA-24/40, or imipenem-sensitive strains formed weak or no biofilm. Conclusions: Coexistence of the bla OXA-51, bla OXA-23 and bla OXA-24/40 like genes, along with formation of strong biofilm, in MDR-AB strains particularly with indiscriminate use of imipenem, complicated treatment of the patients infected with these bacteria in the hospitals understudy.