Abstract: Pathogenic microorganisms in meat are one of the most important factors in human food-borne diseases. In the present study, the prevalence of Salmonella, coliform bacteria, Staphylococcus aureus and Listeria monocytogenes in various yak tissues, and the serological identification and antibiotic resistance of Salmonella were investigated. Totally, 277 samples of muscle and visceral tissues from yaks in Northwest Sichuan plateau were collected including 155 samples from free grazing yaks and 122 samples from stall-fed fattening yaks both without diarrhea symptoms. The results showed that no significant difference in the carrier rate of pathogenic microorganisms in various yak tissues was between two feeding regimens (P > 0.05), but the absolute value of detection rate in free grazing yak was higher than that in stall-fed fattening yak. Different Salmonella serotypes were isolated from yak tissue samples from two different feeding systems. The Salmonella serotypes isolated from stall-fed fattening and grazing yak muscle were S. newport and S. enteritidis, respectively. The Salmonella serotypes isolated from fecal samples of grazing yak were S. typhimurium, S. enteritidis and S. saintpaul, while only S. dublin was isolated from fecal samples of stall-fed fattening yaks. The feeding regimens had no effect on the antibiotic resistance of Salmonella isolated from yaks, and the Salmonella isolated from stall-fed and free grazing yaks showed high resistance to lincomycin (83.33% and 81.82%), tetracycline (66.67% and 63.64%), and midecamycin (66.67% and 72.73%). Overall, the microbiological safety of yaks was identical between two feeding regimens, and the antibiotic resistance of Salmonella isolated from the yaks was high.

Key words: yak, feeding regimens, Salmonella, coliform bacteria, Staphylococcus aureus, Listeria monocytogenes