Contamination, molecular characterization and virulence of Staphylococcus aureus isolated from pork at cold storage...

Staphylococcus aureus has emerged as a growing concern in food safety due to its high environment adaptability in low temperature. While cold-chain storage makes food last longer and slows down growth of most microorganisms, it simultaneously selects cold-tolerant pathogens like S. aureus stay alive throughout the food chain. However, systematic and region-specific investigations into the contamination and characterize of S. aureus isolates from pork stored in cold storage warehouses remain scarce. A total of 344 samples were collected in 23 cold storage facilities for S. aureus detection in Zhejiang Province, China. Finally, 52 isolates were obtained from 40 samples (11.3 %), representing from 13 different cold storage warehouses. Notably, 27 (51.9 %) of the isolates were enterotoxigenic, and 40 (76.9 %) exhibited multi-drug resistance with strong biofilm-forming capacity; among them, 13 were identified as methicillin-resistant S. aureus. Furthermore, all 52 isolates were grouped into 10 Random Amplified Polymorphic DNA clusters and 13 spa types, including the newly prevalent type spa-t20663. The most common sequence types were ST398, ST188, and ST6, which showed close genetic relatedness to other foodborne S. aureus reported in China. In addition, high virulence levels were observed in Galleria mellonella infection models, and ST188 S. aureus isolates caused skin abscesses in rabbits. These findings highlight the widespread contamination, long-term survival potential, virulence traits and molecular diversity of multi-drug resistant S. aureus isolated from frozen pork. Therefore, integrated surveillance and control strategies are urgently needed to mitigate the associated public health risks.