Bacterial Diversity and Antimicrobial Resistance of Microorganisms Isolated from Teat Cup Liners in Dairy Farms in Shandong Province, China

Simple Summary Assessing the quality of raw milk is crucial for humans' well-being. This study aimed to evaluate the bacterial composition and antimicrobial resistance in the tea cup liners of dairy cow milking equipment. The objective was to determine the potential risk of bacterial contamination in raw milk during the milking process and the transmission of antimicrobial-resistant bacteria through milk sources. The study found that Bacillus spp. were the most prevalent bacteria identified on the teat cup liners. A significant proportion of these bacteria showed significant resistance to various antibiotics, such as lincomycin, sulfadiazine, and streptomycin. Multiple antimicrobial resistance genes were also detected, indicating the potential transmission of antimicrobial-resistant bacteria in the milk samples. These findings underscore the imperative to enhance disinfection protocols within dairy farms and milking equipment. The results accentuate the enduring peril of disseminating antimicrobial-resistant bacteria via contaminated milk sources. Taking heed of this finding will contribute to the sustainable development of the dairy industry while mitigating the hazards associated with food safety. Increasing awareness of the potential dissemination of antimicrobial-resistant bacteria through dairy products can foster the implementation of appropriate measures to ensure the secure production and consumption of such products, thereby safeguarding public health and welfare.Abstract Global milk consumption exceeds 800 million tons a year and is still growing. Milk quality and its products are critical to human health. A teat cup makes direct contact with the cow's teats during milking and its cleanliness is very important for the quality of raw milk. In this study, the microorganism from post-milking teat cup liners were collected from six dairy farms in Shandong Province of China, the bacterial species were identified using microbial mass spectrometry, the minimum inhibitory concentrations of the isolated strains against ten antimicrobial agents were determined using the broth microdilution method, and the antimicrobial resistance genes were detected by PCR. The results indicated that the most frequently isolated bacteria in this study were Bacillus licheniformis (39/276, 14.13%), followed by Bacillus pumilus (20/276, 7.25%), Bacillus cereus (17/276, 6.16%), and Bacillus subtili (16/276, 5.80%). The isolates exhibited the highest average resistance to lincomycin (87.37%), followed by sulfadiazine (61.05%) and streptomycin (42.63%); the highest detection rate of resistance genes was Sul1 (55.43%), followed by ant(4') (51.09%), tet(M) (25.36%), blaKPC (3.62%) and qnrS (3.62%). These findings imply the necessity for enhanced measures in disinfecting cow udders and milking equipment, highlighting the persistently challenging issue of antimicrobial resistance in Shandong Province.