Objective Molecular epidemiology, antimicrobial resistance, and evolutionary characteristics of Staphylococcus aureus strains isolated from bovine raw milk at dairy farms in northern Fujian, China were investigated.
Methods From the milk samples collected at 14 dairy farms in 2023-2024, 59 pathogen isolates were undergone whole-genome sequencing using the Illumina platform along with molecular MLST and spa typing, antimicrobial susceptibility testing, and resistance gene profiling. Phylogenetic relationship among the isolates was reconstructed based on core genome single-nucleotide polymorphisms (SNPs), and a global minimal spanning tree (MST) analysis conducted using publicly available sequences from the PubMLST database.
Results Livestock-associated MRSA (LA-MRSA) ST59-t437 was identified for the first time in the dairy specimens from northern Fujian, along with a novel regional clone ST9784-t189. The predominant types of the isolates were ST1-t114 (25.4%) and ST9784-t189 (20.3%). The overall non-susceptibility rate to antimicrobial agent was 45.8% with the highest resistance to penicillin and ampicillin (28.8%), albeit lower than those found in other regions in China. The spa typing had a high discriminatory power for micro-evolutionary analyses. The MST analysis indicated that ST398 and ST1 had dual-core global dissemination lineages, whereas others had geographically limited distributions. The multidrug-resistant (MDR) strains harbored a rich repertoire of resistance genes showing a significant correlation with the molecular type.
Conclusion S. aureus from the dairy farms in northern Fujian displayed considerable genetic diversity and relatively low overall antimicrobial resistance. Nevertheless, the newly identified ST9784 and the first regional LA-MRSA ST59-t437 might still pose a risk of dissemination which required attentive cross-host surveillance by the involved agencies.
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