Evaluation of Multilocus Variable-Number Tandem-Repeat (MLVA-8Orsay) for Typing of Carbapenem-Resistant Acinetobacter baumannii Isolated from Patients in Tehran, Iran

Acinetobacter baumannii has emerged worldwide as a major nosocomial pathogen. The aim of this study was to evaluate the MLVA-8Orsay scheme suitability for clustering and differentiating A. baumannii strains isolated from two hospitals in Tehran. A panel of eight variable-number tandem-repeat (VNTR) markers was used for typing analysis (MLVA-8Orsay) of 89 carbapenem-resistant A. baumannii strains isolated from two hospitals in Tehran. Abaum0845 (S-VNTR marker) was excluded from the MLVA scheme because of its great allelic diversity at this locus. The modified MLVA-7 scheme provided excellent discriminatory power and detected 82 MLVA types among the 83 isolates. Additionally, the great diversity associated with MLVA markers did not permit to apply the previously proposed criteria for clustering the isolates. However, six MLVA complexes were defined assuming a 71% genetic similarity cut-off, corresponding to the existence of identically sized alleles for at least five VNTR markers. The blaOXA-23-like gene (93.2%) was the most prevalent gene in resistant isolates collected from the two hospitals. MLVA-7 discriminatory power was found to be excellent. This method was also appeared to be useful and reliable in epidemiological investigations of A. baumannii strains. MLVA-7 analysis revealed that carbapenemase-carrying A. baumannii isolates might be polyclonal and provided evidence for gene transfer among different strains collected from the two hospitals. Overall, the study provided evidence supporting the use of MLVA-7 scheme as an alternative or complementary method for typing of A. baumannii isolates.