Population-based Study of Carbapenem-resistant Raoultella spp. Reveals Diverse Repertoire of Carbapenemase Genes.

Raoultella species, previously considered an environment bacteria, are emerging as human pathogens. Concerningly, there is a rise in reports of carbapenemase-producing strains. Despite this, specific data on Raoultella planticola and Raoultella ornithinolytica characteristics remain limited. Our study aimed to elucidate the national epidemiology of Raoultella spp. in Israel, characterize their antimicrobial resistance and virulence, and examine the transmission mechanisms of carbapenemases. We conducted a retrospective epidemiological analysis of all Raoultella spp. cases reported to Israel's national surveillance system for carbapenem-producing Enterobacterales between 2011 and 2024. Microbiological characterization and antibiotic susceptibility testing was performed on 32 isolates. Whole-genome sequencing was used to understand the phylogenetic relationships between the isolates, detect antibiotic resistance genes and virulence factors, and identify plasmids. All characterized isolates were found to be multidrug resistant, carried multiple (5-20) antibiotic resistance genes, including at least 1 carbapenemase, and harbored at least 1 plasmid from either Inc or Col incompatibility groups. Two outbreaks were detected among the sequenced isolates. We found increasing incidence of carbapenemase-producing Raoultella cases, and their involvement in healthcare outbreaks.