Identification of a novel SXT/R391 integrative and conjugative element harboring blaNDM-1 in a clinical Providencia huaxiensis isolate

In recent years, clinical Providencia species harboring carbapenemase-encoding genes have been increasingly reported, posing significant challenges in public health. However, Providencia huaxiensis ( P. huaxiensis ) isolates producing NDM have rarely been documented. Here, we report a carbapenem-resistant Providencia strain, PR66, which was initially misidentified as P. rettgeri . Antimicrobial susceptibility testing revealed resistance to all tested agents, including carbapenems. Species-level identification was confirmed using the average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH). Whole-genome sequencing and bioinformatics analysis revealed that PR66 possesses a circular chromosome and three plasmids. The chromosome and plasmid pPR66.2 encode multiple resistance genes, including bla NDM-1 , bla OXA-4 , bla OXA-10 , bla MOX-3 , aph(3’)-Ia , aph(3”)-Ib , aph(3’)-VIb , aph(6)-Id , aac(6’)-Ib3 , ant(2”)-Ia , aadA , tet(B) , among others. Notably, the bla NDM-1 gene is located on a novel integrative and conjugative element (ICE), ICE Phu Chn-PR66, which also harbors additional resistance genes. This ICE spanned 127,074 bp (positions 3,989,454–4,116,527 bp) and had a GC content of 48.6%. It was site-specifically integrated into the prfC locus of the PR66 chromosome. Conjugation and genetic stability assays confirmed the successful transfer of bla NDM-1 to Escherichia coli C600, with stable inheritance in the recipient strain. These findings underscore the role of ICEs in disseminating carbapenem resistance within P. huaxiensis and potentially across other bacterial species.