Genomic surveillance of multidrug-resistant Enterobacterales in a long-term care facility in Northern Italy based on a point prevalence screening.

Long-term care facilities (LTCFs) are increasingly recognised as settings where multidrug-resistant organisms (MDROs) persist and circulate. A point prevalence screening study conducted in 2022 in an LTCF in the Autonomous Province of Bolzano/Bozen, Northern Italy, provided a collection of MDR Enterobacterales isolates from residents and staff. This study aimed to characterise the clonal structure, transmission dynamics, and resistance mechanisms of these isolates through high-resolution genomic analysis. Whole-genome sequencing was performed on third-generation cephalosporin- and/or carbapenem-resistant isolates of Klebsiella pneumoniae, Escherichia coli, Morganella morganii, and Proteus mirabilis. Isolates underwent core genome multilocus sequence typing, phylogenetic reconstruction, and resistance gene profiling using Kleborate and ResFinder. K. pneumoniae isolates formed five major clusters, with ST39 confined to a single section, suggesting intra-section transmission. ST405 and ST307, both high-risk clones, were also detected, with ST307 harbouring the carbapenemase gene blaKPC-3. CTX-M-15 was present in 90% of K. pneumoniae isolates. E. coli isolates showed high genomic diversity with limited evidence of clonal transmission. M. morganii and P. mirabilis displayed mixed patterns, with sporadic introductions and one clonal cluster for P. mirabilis. Genomic surveillance revealed complex transmission networks within this LTCF, involving both clonal expansion and heterogeneous strain circulation. Organisational factors such as patient transfers, shared staff, and communal living likely contributed to MDROs dissemination. The predominance of CTX-M-15 and detection of carbapenemase-producing K. pneumoniae underscore the need for targeted infection control strategies. Integration of genomic data with contextual factors supports continuous genomic monitoring, antimicrobial stewardship, and environmental decontamination in LTCFs.