Epidemiology and molecular typing of multidrug resistant Acinetobacter baumannii burn wound isolates from six Chinese provinces.

Acinetobacter baumannii (A. baumannii) is a pathogen that opportunistically infects patients in healthcare settings and poses a significant threat to human health due to its widespread resistance to antimicrobial agents. The temporal and regional distribution of A. baumannii in China is continually evolving, necessitating comprehensive surveillance to examine the prevalence, molecular characteristics, and clonal relationships of antimicrobial resistance determinants in burn wound A. baumannii isolates collected from six major Chinese provinces during 2016-2020. To address this need, we analyzed a total of 415 distinct A. baumannii isolates that were obtained from burn patients. Antimicrobial susceptibility testing was performed using the Kirby Bauer disk diffusion method, while genetic relatedness of the 415 isolates was assessed by utilizing multilocus sequence typing (MLST) and eBURST analysis. Additionally, the housekeeping genes and a comprehensive panel of drug resistance genes, including β-lactamases, membrane permeability factors, and efflux pump systems, were detected by multiplex PCR to elucidate their resistance mechanisms. Our analysis revealed that among the 415 isolates, 384 (92.5%) were classified as multidrug-resistant (MDR), with regional rates ranging from 88.2 to 96.0%. Additionally, 38 (9.2%) isolates were classified as extensively drug-resistant (XDR). All strains showed resistance to multiple antibiotics, except for lower resistance to Tigecycline (TGC) and Cefoperazone/sulbactam (CSL), suggesting their potential therapeutic utility. By MLST, all isolates represented 122 identified STs (sequence types). eBURST analysis identified the 415 isolates into 17 clonal complexes (CCs) in which CC1660 and CC1417 were considered large CCs with at least 100 isolates in each CC. Importantly, our investigation identified a notable epidemiological shift: CC1417 and CC1660 instead of CC92 have become the novel predominant strains in burn wound isolates of these Chinese provinces, and the predominant strain varied in separate regions. Consistently, our investigation identified ST1417, ST1660, and ST1145 instead of ST208 as predominant sequence types, indicating a notable shift in regional epidemiological patterns for burn wound A. baumannii isolates. In addition, the carrying rates of multiple antibiotic-resistant genes maintain a high level, indicating the evolution of strain genes and the severe drug resistance situation in burn wound isolates of these Chinese provinces. As a result, epidemiological surveillance and genetic evolution analysis of A. baumannii is of great significance to provide more strategies for the prevention of nosocomial infection and clinical treatment.