Emergence and traceability of Salmonella enterica serotype Mbandaka harboring blaOXA-10 from chickens in China.

Salmonella enterica serotype Mbandaka (S. Mbandaka), a multi-host adapted non-typhoidal Salmonella, has emerged as a significant public health concern in recent years. In this study, we isolated S. Mbandaka strains carrying a multidrug-resistant IncHI2A/IncHI2 plasmid from deceased chickens in China and performed whole-genome sequencing and comparative genomic analyses to investigate their global dissemination and evolutionary adaptation. The multidrug-resistant IncHI2A/IncHI2 plasmid in isolate YK35 harbored multiple antibiotic resistance genes (ARGs) including blaOXA-10, which was firstly observed in S. Mbandaka in China. It exhibited high sequence identity with IncHI2A/IncHI2 plasmids identified in other bacterial species, including S. Typhimurium, Klebsiella aerogenes, and E. coli, which suggested the cross-species dissemination of IncHI2A/IncHI2 plasmids and ARGs. Global genomic epidemiology classified S. Mbandaka strains into seven distinct clades, with the majority originating from the USA and the UK. The pan-genomic analysis indicated an open pan-genome structure, with continuous expansion of accessory genes, particularly those associated with replication, recombination, repair, and defense mechanisms, underscoring the evolutionary adaptation of S. Mbandaka to external environments. Evolutionary analysis further traced the international transmission routes of S. Mbandaka, revealing potential cross-regional spread, particularly from the USA and the UK to other countries, including China. The findings emphasize the global spread and evolutionary adaptation of S. Mbandaka, likely driven by international trade and horizontal gene transfer, including the acquisition of ARGs, which have contributed to its increasing public health risks. This study underscores the urgent need for enhanced surveillance and control measures to mitigate the spread of S. Mbandaka and its antibiotic resistance, particularly in the context of global food supply chains and international trade.