Carbapenem-Resistant <i>Citrobacter koseri</i>: An Emerging Concern in Long-term Care Hospital

Background: Citrobacter spp.are known opportunistic pathogens.Recent reports have indicated concerningly high rates of carbapenem resistance in long-term care hospitals.In this study, we investigated the characteristics of carbapenemase genotypes in carbapenem-resistant Citrobacter spp.(CR-Citrobacter spp.) isolated from clinical and surveillance specimens.Methods: CR-Citrobacter spp.isolates were collected from Seoul Clinical Laboratories in 2023.The isolates underwent multiplex polymerase chain reaction (PCR) analysis for the detection of six carbapenemase genotypes (KPC, GES, IMP, NDM, VIM, and OXA-48-like) using the PANA Real Typer CRE Kit (PANAGENE, Korea).Results: Among 329 CR-Citrobacter spp.isolates, 289 (87.9%) were from patients aged 60 years or older, with the majority isolated from long-term care hospitals (255, 77.5%).C. koseri was predominant in both the clinical and surveillance isolates at 84.7 % (72/85) and 67.6 % (165/244), respectively.KPC (76.5%) was the most common carbapenemase genotype detected in the clinical isolates, followed by OXA-48-like (11.8%) and NDM (8.2%).Double carbapenemase genotypes were detected in eight isolates (2.4%). Conclusion:This study revealed a high prevalence of CR-Citrobacter spp., particularly C. koseri, in long-term care hospitals.The predominance of KPC-producing C. koseri highlights the need for enhanced surveillance and infection control in long-term care hospitals.