Multicenter retrospective genomic characterization of carbapenemase-producing Acinetobacter baumannii isolates from Jiangxi patients 2021–2022: identification of a novel international clone, IC11

ABSTRACT This study aimed to characterize carbapenem-resistant Acinetobacter baumannii (CRAB) isolates from Jiangxi patients using whole-genome sequencing (WGS). We subjected 100 clinical CRAB strains isolated from the three local largest teaching hospitals to WGS and antimicrobial susceptibility testing. Molecular epidemiology was investigated using multilocus sequence typing, core genome multilocus typing, core genome single-nucleotide polymorphism phylogeny, and pulsed-field gel electrophoresis. The most prevalent acquired carbapenemase was bla OXA-23 , predominant in all isolates (100%). Isolates belonging to the dominating international clone IC2 accounted for 92% of all isolates. International IC11 (ST164 Pas /ST1418 Ox ) clone was found in an additional 8% (eight isolates), with seven isolates (87.5%) carrying an acquired additional bla NDM-1 carbapenemase. The oxa23 -associated Tn 2009 , either alone or in a tandem repeat structure containing four copies of bla OXA-23 , was discovered in 62% (57 isolates) of IC2. The oxa23 -associated Tn 2006 was identified in 38% (35 isolates) of IC2 and all IC11 isolates. A putative conjugative RP-T1 (formerly RepAci6) plasmid with bla OXA-23 in Tn 2006 within AbaR4, designated pSRM1.1, was found in IC2 A. baumannii strain SRM1. The bla NDM-1 gene found in seven IC11 isolates was located on a novel Tn 6924 -like transposon, a first-time report in IC11. These findings underscore the significant importance of real-time surveillance to prevent the further spread of CRAB. IMPORTANCE Carbapenem-resistant Acinetobacter baumannii (CRAB) is notorious for causing difficult-to-treat infections. To elucidate the molecular and clinical epidemiology of CRAB in Jiangxi, clinical CRAB isolates were collected and underwent whole-genome sequencing and antibiotic susceptibility phenotyping. Key findings included the predominance of OXA-23-producing IC2 A. baumannii , marked by the emergence of OXA-23 and NDM-1-producing IC11 strains.