Dissemination of <i>bla</i> _OXA-23 , <i>bla</i> _OXA-24 , <i>bla</i> _OXA-58 , and <i>bla</i> _NDM-1 Genes of <i>Acinetobacter baumannii</i> Isolates from Four Tertiary Hospitals in Thailand

Acinetobacter baumannii is a major threat to public health due to the emergence and dissemination of antibiotic-resistant strains. The purpose of this study was to determine the molecular epidemiology of antibiotic-resistant A. baumannii isolates collected from four tertiary hospitals in Thailand during the period November 2013-February 2015. We screened 339 A. baumannii, nonrepetitive clinical isolates to determine drug susceptibility. Among all isolates, we found that 7.9% was nondrug-resistant A. baumannii (NR-AB). Carbapenem-resistant A. baumannii (CR-AB) strains accounted for 84.9% of the total isolates, with extensively drug-resistant A. baumannii (XDR-AB) accounting for 7.9% of the total isolates. We further investigated class D carbapenemase genes using multiplex-PCR amplification and class B metallo-β-lactamase genes, including bla_IMP, bla_VIM, and bla_NDM-1 genes, using PCR and sequencing methods. We found that 300 (88.5%) isolates carried acquired class D carbapenemase genes, including bla_OXA-23 (82.6%), bla_OXA-24 (0.3%), and bla_OXA-58 (6.5%). The genes bla_IMP and bla_VIM were not detected in any isolates. The bla_NDM-1 was detected in 31 isolates from two hospitals (9.1%). All of the bla_NDM-1-positive A. baumannii (NDM-AB) had ISAba125 sequences upstream of the bla_NDM-1 gene. A coexistence of three resistance genes-bla_OXA-23-bla_OXA-58-bla_NDM-1-was found in one isolate. A repetitive element palindromic-PCR (REP-PCR) revealed that all A. baumannii isolates were genetically diverse and could be divided into 33 genotypes. Only three genotypes were found to be predominant in all hospitals. Data from our study indicate the widespread emergence of multiple resistance determinants in A. baumannii isolates in Thailand, suggesting the need for more stringent infection control measures.