Comparative genomic insights into carbapenem-resistant versus susceptible Acinetobacter baumannii in Shanghai hospital settings: a multi-center molecular surveillance study.

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (CRAB) is priority pathogen for nosocomial infection control worldwide. This study aimed to elucidate differences in distribution, genotyping and antimicrobial resistance patterns between CRAB and carbapenem-susceptible Acinetobacter baumannii (CSAB) strains isolated from healthcare environments.

MATERIALS AND

METHODS

A total of 1,812 environmental samples were collected from 10 medical institutions in Pudong New Area between June and December 2024 for the identification of A. baumannii. Antimicrobial susceptibility testing, whole-genome sequencing, and bioinformatic analysis were performed to reveal molecular characteristics of A. baumannii.

RESULTS

A total of 81 A. baumannii strains were detected, with 39.51% CRAB (n = 32) and 60.49% CSAB (n = 49). CRAB strains were highly prevalent in intensive care units (ICUs, accounting for 83.33%) and patient-contact items, whereas CSAB were more evenly distributed. MLST analysis identified ST2 as dominant CRAB clone (78.13%), followed by ST164 (18.75%). CRAB isolates demonstrated 100% resistance to multiple antibiotics such as piperacillin/tazobactam and ciprofloxacin, whereas all CSAB isolates were susceptible to tested antibiotics except one ampicillin/sulbactam-resistant isolate. Carbapenem resistance in CRAB was predominantly mediated by class D carbapenemases, with carriage rate of the bla OXA-23 gene reaching 96.88%. Notably, six ST164 isolates co-harbored class B and class D carbapenemase genes, which may elevate resistance severity. Bioinformatic analysis indicated that 22.20% of resistance plasmids in CRAB were predicted to be conjugative. CRAB exhibited a more diverse and extensive virulence gene profile than CSAB strains.

CONCLUSIONS

The ICU environment was critical for CRAB control. ST2 and ST164 represented clones worthy of attention. CRAB exhibited stronger resistance, harbored more putatively conjugative plasmids and richer virulence-associated genes than CSAB, highlighting the need for targeted disinfection and surveillance of prevalent clones.