Phenotypic and Genotypic Characterization of Carbapenem-Resistant Acinetobacter baumannii Clinical Isolates: Co-Existence of blaOXA-23 and blaNDM-1 in a Vietnamese Tertiary Hospital.

BACKGROUND

Acinetobacter baumannii has emerged as an important opportunistic pathogen due to its increasing resistance to carbapenems, which severely limits therapeutic options. This study is aimed at characterizing the phenotypic resistance profiles and distribution of carbapenemase-encoding genes among clinical A. baumannii isolates collected from a tertiary-care hospital in southern Vietnam.

METHODS

A retrospective study was conducted on 156 A. baumannii isolates collected at the University Medical Center Ho Chi Minh City between January and December 2024. Antimicrobial susceptibility testing was performed using the BD Phoenix M50 system. Carbapenemase-encoding genes, including blaOXA-23, blaOXA-58, blaNDM-1, and blaKPC, were detected using multiplex real-time PCR.

RESULTS

Among the 156 isolates, 70.51% were identified as carbapenem-resistant A. baumannii (CRAB). Most CRAB isolates originated from respiratory specimens (83.64%) and intensive care units (60%). CRAB isolates exhibited extensive multidrug resistance, with resistance rates ranging from 76% to > 96% for most cephalosporins, fluoroquinolones, and aminoglycosides. In contrast, minocycline retained the highest in vitro activity, with a resistance rate of only 10%. The most prevalent carbapenemase gene was blaOXA-23 (73.6%), followed by blaNDM-1 (52.7%) and blaOXA-58 (20.0%). Overall, 95.45% of CRAB isolates were phenotypically identified as carbapenemase-producing A. baumannii (CP-AB). The co-occurrence of blaOXA-23 and blaNDM-1 was the most common gene combination, detected in 23.64% of CRAB isolates.

CONCLUSION

This study demonstrates a high burden of CRAB in a Vietnamese tertiary hospital, largely driven by the co-existence of blaOXA-23 and blaNDM-1. The identification of carbapenem-resistant isolates lacking phenotypic carbapenemase activity suggests the involvement of alternative, nonenzymatic resistance mechanisms. Continuous molecular surveillance and strengthened antimicrobial stewardship are urgently needed to limit CRAB dissemination in Vietnam.