Clonal relatedness of carbapenem-resistant Acinetobacter baumannii: high prevalence of ST136 in a burn center.

Background: Carbapenem-resistant Acinetobacter baumannii (CRAB) is a global health crisis. This study aimed to determine the clonal relatedness of antibiotic-resistant A. baumannii isolates in hospitalized patients who suffered from burn wound infection.

Methods: One hundred and six A. baumannii isolates from 562 patients with burn wound infections, were identified and examined for antimicrobial susceptibility. Detection and characterization of carbapenem-hydrolyzing class D OXA-type beta-lactamases (CHDLs) were performed by PCR assays. The clonal relatedness of A. baumannii isolates was determined by multilocus sequence typing (MLST) according to the Pasteur scheme, dual-sequence typing of bla-like and ampC genes, and RAPD-PCR method.

Results: All isolates were carbapenem-resistant while susceptible to colistin, minocycline, doxycycline, and ampicillin-sulbactam. The intrinsic bla-like was detected in all isolates, and bla-like was identified in 92.5% of isolates. However, bla-like and bla-like genes were not detected among isolates. Four distinct bla-like alleles were determined as follows: bla (67.0%), bla (9.4%), bla (17.0%), and bla (6.6%) and four ampC (bla) allele types including ampC-25 (6.6%), ampC-39 (9.4%), ampC-1 (17.0%), and bla (67.0%) were identified. MLST (Pasteur scheme) analysis revealed four ST types including ST136 (singleton), ST1 (CC1), ST25 (CC25), and ST78 (singleton) in 71, 18, 7, and 10 of A. baumannii strains, respectively. Five RAPD clusters including A (1.9%), B (26.4%), C (57.5%), D (7.5%), and E (1.9%) were characterized and 5 (4.7%) strains were found to be singletons.

Conclusion: The present study demonstrated that there was a high prevalence of bla-like producing CRAB in the clinical setting. The majority of isolates belonged to ST136 (singleton). However, bla-like producing multi-drug resistant international clones including ST1, and emerging lineages (e.g. ST25 and ST78) were also identified. Interestingly, in this study ST2 was not detected.