Emergence of Carbapenem-Hydrolyzing Oxacillinases in Acinetobacter baumannii in Children from Croatia.

Introduction: Carbapenem resistance in Acinetobacter baumannii can be mediated by carbapenemases of class A, class B metallo-beta-lactamases (MBLs), and class D carbapenem-hydrolyzing oxacillinases (CHDL). The aim of the study was to investigate the antimicrobial susceptibility and beta-lactamase production of carbapenem-resistant A. baumannii isolates (CRAB) from the Children's Hospital Zagreb, Croatia. Methods: A total of 12 A. baumannii isolates collected between August 2016 and March 2018 were analyzed. Antibiotic susceptibility was determined by the broth microdilution method. The presence of MBLs was explored by combined disk test with EDTA. The presence of carbapenemases of class A, B, and D was explored by PCR. The occurrence of the ISAba1 upstream of the bla(OXA-51-like) or bla(OXA-23-like) was determined by PCR mapping. Epidemiological typing was performed by determination of sequence groups (SG). Genotyping was performed by SG determination, rep-PCR, and MLST. Results: All CRAB were resistant to piperacillin/tazobactam, ceftazidime, cefotaxime, ceftriaxone, cefepime, imipenem, meropenem, gentamicin, and ciprofloxacin. Moderate resistance rates were observed for ampicillin/sulbactam (67%) and tigecycline (42%). The isolates were uniformly susceptible to colistin. PCR revealed the presence of genes encoding OXA-24-like CHDL in nine and OXA-23-like CHDL in three isolates. bla(OXA-51) genes were preceded by ISAba1. PCR for the common MBLs in Acinetobacter was negative. All isolates belonged to SG 1 corresponding to ICL (International Clonal Lineage) II. Rep-PCR identified four major clones. Conclusions: The study found OXA-24-like beta-lactamase to be the dominant CHDL among children'sCRAB. The predominant spread of OXA-24-like is in contrast with the recent global dissemination of OXA-23 reported all over the world. In contrast to the previous studies in which emergency of OXA-24-like positive isolates was monoclonal, we found considerable genetic diversity of the isolates.