Molecular Epidemiology of NDM-Producing Escherichia coli Isolates in Croatia from March 2023 to March 2024

In 2023, the European Centre for Disease Prevention and Control surveillance report highlighted an increasing number of carbapenem-resistant Escherichia coli isolates carrying the less common bla_NDM-5 variant in Europe. The aim of this study was to investigate the molecular epidemiology of NDM-producing (New Delhi metallo-β-lactamase) E. coli isolates collected in Croatia over a one-year period. A total of 160 carbapenemase-producing E. coli isolates were reported through national surveillance in Croatia between March 2023 and March 2024. Whole-genome sequencing was performed on 22 NDM-producing E. coli isolates. Phylogenetic analysis identified 17 sequence types, indicating high diversity and polyclonal spread. High variability in resistome profiles and co-occurrence of resistance genes across multiple antimicrobial classes indicate multidrug resistance. The predominant bla_NDM variant was bla_NDM-1 (77.27%), followed by bla_NDM-5 (22.73%). Co-occurrence of bla_NDM with extended-spectrum β-lactamase (ESBL) encoding genes was detected in 12/22 isolates (54.55%). Plasmid analysis identified 22 different replicon types, with IncFII (54.54%) and IncA/C2 (45.45%) being the most frequent. Our findings provide insights into the molecular epidemiology of NDM-producing E. coli at the national level, highlighting the presence of the bla_NDM-5 variant. These results emphasize the need for genomic surveillance and strengthened infection control strategies to better understand and limit its spread.