Occurrence, Antimicrobial Resistance Patterns, and Genetic Characterization of Isolated from Raw Milk in the Dairy Farms over Two Seasons in China.

This study investigated the occurrence and resistance rates of strains isolated from raw milk in the dairy farms over two seasons (spring and autumn) and across four regions that included 11 provinces in China. In total, 750 raw milk samples from the 405 dairy farms were collected. Fifteen antimicrobial agents were tested for antimicrobial resistance via disk diffusion tests, and PCR tests were performed to identify drug resistance genes of isolates. Out of 750 samples, 276 (36.8%) were positive for , with 150 (41.1%) being positive in spring and 126 (32.7%) being positive in autumn. The occurrence rate of in northeastern China (45%) was higher than that in western China (33%) and southern China (31.9%), respectively, and the rate significantly ( < 0.05) differed from those of western China and southern China. Of 276 isolates, 261 (94.6%) strains were resistant to more than 1 antimicrobial drug, and 193 (69.9%) strains were multidrug resistant. The Z (46.3%), (35.5%), and (27.2%) genes were detected at a high frequency in the strains. Our data revealed a variation ( < 0.05) in the resistance patterns in the different regions and across the two seasons. The occurrence and drug resistance rates of isolated from raw milk obtained from dairy farms may still cause severe problems in China.