Distribution of Staphylococcus chromogenes and Mammaliicoccus sciuri across cows, farm environment, and workers in 3...

Non-aureus staphylococci and mammaliicocci (NASM) are among the most frequently detected pathogens in bovine mastitis, yet their dominant species, distribution across the cow-human-environment interface, within-herd population structure, and potential epidemiologic links remain incompletely described in China. We conducted a cross-sectional survey in 3 commercial Chinese dairy herds using distinct bedding systems [manure solids (MNS), new sand (NS), and sawdust]. Samples were collected from lactating cows and milk-fed calves (multiple body sites), mastitic milk (clinical and subclinical), farm environment, and workers. NASM were identified by MALDI-TOF MS and tuf sequencing, and the 2 most frequently isolated NASM species were further characterized by core-genome MLST (cgMLST). NASM detection in mastitic milk differed across herds, being highest in the MNS herd and lowest in the NS herd. Eleven NASM species were isolated from milk, with Staphylococcus chromogenes and Mammaliicoccus sciuri as the 2 most frequently isolated NASM species. S. chromogenes (S. chromogenes vs M. sciuri: 27.5 vs 19.5%) was more frequently detected in host-associated samples, whereas M. sciuri (M. sciuri vs S. chromogenes: 34.7 vs 10.4%) was enriched in environmental samples; rectum and bedding represented the main carriage sites for S. chromogenes (38.3%) and M. sciuri (44.3%), respectively. Herd-level patterns were distinct: the MNS herd was dominated by M. sciuri across sources (cattle: 45.6%; environment: 69.1%; humans: 13.9%), whereas the NS (cattle: 18.6%; environment: 13.2%; humans: 11.9%) and sawdust (cattle: 43.9%; environment: 21.1%; humans: 16.7%) herds were dominated by S. chromogenes. Detection of M. sciuri from mastitic milk mirrored its environmental occurrence across herds, whereas S. chromogenes remained the most common species in mastitic milk in all herds. cgMLST revealed substantial genetic diversity in both species, with related isolates detected among bovine, human, and environmental sources. In addition, identical S. chromogenes isolate pairs were detected between milk and bedding samples, and identical M. sciuri isolate pairs were detected between the nasal vestibules of a milk-fed calf and a lactating cow. Overall, the 2 dominant NASM species had marked herd-specific distribution patterns across herds with distinct bedding systems, underscoring the importance of species-targeted control focused on key sources and management practices.