Molecular characterization of oxacillinases among carbapenem-resistant Acinetobacter baumannii nosocomial isolates in a Saudi hospital

Background: Acinetobacter baumannii has successfully become a significant nosocomial pathogen because of its remarkable ability to acquire antibiotic resistance and to survive in nosocomial environments. This study aimed to determine the drug susceptibility patterns and the distribution of four subgroups of carbapenem-hydrolyzing class D -lactamases (OXA-carbapenemases), as well as their insertion sequences (ISAba1), among A. baumannii nosocomial isolates from a Saudi tertiary care hospital. Methods: A total of 108 non-duplicate A. baumannh isolates were identified, and their susceptibilities to different antibiotics were determined using the breakpoint method. Isolates were then subjected to multiplex-PER targeting bla(OXA) genes. Results: More than 75% of the isolates showed resistance to different antibiotics. The rates of susceptibility to colistin, meropenem, imipenem and trimethoprim sulfamethoxazole were 95.6, 50, 48.1 and 34.3%, respectively. All isolates possessed a bla(OXA-51-like) gene. Of the 56 carbapenem-resistant isolates, 48 isolates (85.7%) carried bla(OXA-23-like), 3 isolates (5.4%) carried bla(OXA-40-like) and two isolates (3.6%) had bla(OXA-58-like) genes. The ISAbal element was found upstream of the bla(OXA-23) and bla(OXA-24) genes in 40 (71.4%) and 3 (5.4%) isolates, respectively, while it was detected upstream of biaoxA.51 in only one (1.8%) isolate. Conclusion: Our findings further illustrate the challenge of increasing carbapenemresistance in A. baumannii isolates in Saudi Arabia. The high distribution of class D carbapenemase-encoding genes, mainly ISAba1/OXA-23 and ISAba1/OXA-24 carbapenemases, is worrisome and presents an emerging threat in our hospital. Local molecular surveillance is essential to help control carbapenem-resistant A. baurnannii nosocomial infections and to prevent DNA exchange among endemic nosocomial pathogens. (C) 2014 King Saud Bin Abdulaziz University for Health Sciences. Published by Elsevier Limited. All rights reserved.