Genomic and phenotypic insights into ST164 bla_NDM-1-positive Acinetobacter baumannii from intestinal colonization in...

Carbapenem-resistant Acinetobacter baumannii (CRAB) poses a critical global threat, especially in ICUs. Yet, reports on ST164 CRAB harboring bla_NDM-1 remain scarce. This study investigates two clinical CRAB isolates, L4773hy and L4796hy, derived from intestinal colonization in Hangzhou, China, focusing on their phenotypic and genomic characteristics as well as the broader transmission of ST164 A. baumannii.

Bacterial identification was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) mass spectrometry. Antimicrobial susceptibility was assessed via agar and broth microdilution. Whole-genome sequencing employed Illumina NovaSeq 6000 and Oxford Nanopore platforms. Resistance genes, insertion elements, transposons, and integrons were detected using ResFinder, PlasmidFinder, VFDB, ISFinder, pdifFinder, and IntegronFinder. Strains were typed by MLST, and a phylogenetic tree was constructed with kSNP3.0. Genetic environment diagrams were generated using Easyfig 2.2.5.

Two bla_NDM-1-carrying A. baumannii isolates exhibiting extensive resistance to carbapenems, cephalosporins, and fluoroquinolones. Whole-genome sequencing and genetic environment analysis revealed the presence of a conserved structural sequence (ISAba14-ISAba14-aphA-ISAba125-bla_NDM-1-ble_MBL) on their chromosomes. Phylogenetic and clonal dissemination analysis showed that ST164 CRAB is primarily distributed in China and exhibits clonal spread. Pathogenicity studies indicated that bla_NDM-1-positive ST164 strains have enhanced survival under immune pressure but do not display increased virulence in infection models.

This study provides the genomic and phenotypic characterization of intestinally colonized ST164 bla_NDM-1 positive CRAB in Hangzhou, China. The elucidation of the genetic environment of bla_NDM-1 further confirms the clonal dissemination of ST164 isolates, highlighting the importance of enhanced surveillance and infection control measures to mitigate the spread of these multidrug-resistant pathogens.