Evidence of Interruption of the comM Gene in a Large Series of Clinical Isolates of Multidrug-Resistant Acinetobacter baumannii

Recent studies have recognized the ATPase-encoding comM gene as a hot spot for the integration of Acinetobacter baumannii resistance islands (RIs). Despite the circulation of high numbers of multidrug-resistant A. baumannii (MDR-AB) isolates in Middle East countries, no information is available about the interruption of comM and subsequent transposition into comM in isolates belonging to the global clones (GC) GC1, GC2, or GC3. In this study 401 A. baumannii isolates from hospitals in Tehran, Iran, were included. The resistance profile was determined by disc diffusion against 22 antibiotics. PCR was used to assess the GC type, presence of the comM gene, and the boundary junctions (J1 and J2) of RIs. Most of the MDR-AB isolates (384 of 388; 98%) and more than half of the susceptible A. baumannii isolates (9 of 13; 69%) had interrupted comM gene-carrying integrative elements. Among the isolates tested, 57 belonged to GC1, 86 to GC2, and 8 to GC3. A set of 250 isolates showed distinct patterns of allele-specific PCR for ompA, csuE, and blaOXA-51-like genes. All but 2 of the GC1 isolates and 2 of the GC2 isolates contained interrupted comM genes. Four A. baumannii isolates harbored intact comM, but were multiply resistant to antibiotics. This study demonstrated that the comM gene is targeted by transposons in Iranian MDR-AB isolates belonging to different GCs. The data also showed that the carriage of interrupted comM is not exclusive to MDR isolates of A. baumannii.