Title : Investigation of molecular epidemiology of carbapenem-resistant Acinetobacter baumannii group in Taiwan
Abstract:
The Acinetobacter baumannii group (AB-group), encompassing A. baumannii, A. pittii, A. nosocomialis, along with recent additions A. seifertii and A. dijkshoorniae, have emerged as prominent nosocomial pathogens with a global presence. Infections with antibiotic-resistant Acinetobacter spp., especially carbapenem-resistant A. baumannii (CRAB) or multidrug-resistant A. baumannii, are associated with an elevated risk of mortality compared to susceptible strains, and their prevalence in nosocomial infections has been steadily rising. CRAB strains were categorized as a critical priority pathogen by the World Health Organization toward combatting increasing antibiotic resistance and developing advanced therapy. Molecular characterization techniques, such as blaOXA-51-like PCR and rpoB sequencing, exhibit superior discriminatory capability compared to conventional approaches for the AB group. A total of 492 Acinetobacter spp. strains were collected from two hospitals in Taiwan and were classified using MALDI-TOF MS, blaOXA51-like PCR and rpoB sequencing: 94.5% (n=465) of A. baumannii and 5.5% (n=27) of non-A. baumanniii (NAB). Out of 492 isolates, 49.3% (n = 240) were defined as carbapenem-resistant (CR) strains with the MIC value of imipenem (IMP) and meropenem (MEM) ≥ 4 mg/L, including CRAB (n = 237) and carbapenem-resistant NAB (CR-NAB) (n = 3). All CRAB and CR-NAB were screened carbapenemase genes by multiplex PCR assay. All CR isolates were negative for blaOXA-143-like, blaKPC, blaGES, blaVIM, blaSPM, blaGIM, and blaSIM. Out of 237 CRAB strains, 72.6% carried blaOXA-23-like, 22.8% carried blaOXA-24-like, 3.3% were co-carriage of blaOXA-23-like-blaOXA-24-like and 1.3% harbored blaOXA51-like only. Among CR-NAB strains, 2 strains were co-carriage of blaOXA58-like and blaIMP, and one strain carried blaNDM-1. The rates of the predominant carbapenemase genes from 2015 to 2021 were further compared and showed slight changes during these years. Interestingly, we found a strain with harbored blaNDM-1, featuring the rpoB allele (rpoB-85) closely aligned with A. seifertii, and exhibiting remarkably high MIC levels of 128 mg/L for both IMP and MEM. Whole-genome Sequencing indicated that the strain harbored a plasmid-borne blaNDM-1, designated pAS39-2 (approximately 47 kb). pAS39-2 also carried genes conferring resistance to aminoglycosides and bleomycin and featured a Ti-type conjugative operon. This plasmid was transferred effectively from A. seifertii to A. baumannii strains by in vitro conjugation. Moreover, pAS39-2 closely resembled plasmidsfound in A. soli and A. pittii in Taiwan, harboring the potential for transmissible multidrug resistance and contributing to the escalating spread of antimicrobial resistance. The current study reports on the molecular epidemiology of AB group isolates collected over a span of 6 years, revealing the carriage rate and types of carbapenemases present in A. baumannii and NAB strains in Taiwan. These findings offer valuable insights for monitoring the epidemiology and dissemination of this pathogen.
