Molecular epidemiology and evolutionary analysis of multidrug-resistant Acinetobacter baumannii SToxf2499 clone at a tertiary hospital in Tianjin, China.

Acinetobacter baumannii has been increasingly reported in nosocomial settings worldwide. However, the molecular characteristics and evolutionary history of A. baumannii in Tianjin-area hospitals in China have not been elucidated. In this study, we conducted a molecular epidemiological investigation of 114 A. baumannii isolates in Tianjin, China across 7 mos. Whole-genome sequencing was used to determine genomic species, sequence types, antimicrobial-resistant genes, and single-nucleotide polymorphism-based phylogenetic analysis. The genetic environment was analyzed using Nanopore sequencing. Among the 114 A. baumannii strains tested, 89.5% exhibited resistance to carbapenems. Whole-genome sequencing revealed that SToxf2499 A. baumannii accounted for 82.4% (94 of 114) of the isolates and was phylogenetically identified as a branch of STpas2. Phylogenetic analysis indicated that the SToxf2499 A. baumannii strains had undergone clonal spread within the hospital. However, these isolates were only distantly related to SToxf2499 A. baumannii isolates from other regions of China. Importantly, nanopore sequencing indicates that SToxf2499 strains have evolved by acquiring an IS15D1-composite transposon. This acquired element harboured a multidrug-resistant gene cluster and exhibited a high degree of similarity and coverage with that of A. baumannii SToxf191 from South Korea. This study identifies and describes the first large-scale emergence of SToxf2499 A. baumannii in Tianjin, China. Our study highlights that the continuous dissemination of SToxf2499 A. baumannii and its acquisition of the IS15D1-composite transposon constitute a serious threat to patients who are hospitalized.