OBJECTIVETo investigate antimicrobial resistance profiles and genetic diversity of staphylococcus aureus isolated from lactating cows of 5 provinces in China, 2013.

METHODSA total of 680 samples were collected from 15 herds (12 farms, 3 artels) in 5 provinces of China in 2013, including swabs of extramammary sites (bovine teat skin and milking machine liners) and quarter milk samples from lactating cows diagnosed with subclinical mastitis. The antimicrobial resistance of the isolates were tested by broth microdilution method and the genotypes were determined by PFGE (pulsed-field gel electrophoresis) method.

RESULTSA total of 111 isolates were isolated and identified as staphylococcus aureus. Resistance to penicillin (90.1% (100/111)), erythromycin (48.6% (54/111)), ciprofloxacin (36.9% (41/111)), clindamycin (27.9% (31/111)), gentamycin (18.9% (21/111)), chloramphenicol (9.0% (10/111)), tetracycline (7.2% (8/111)) of these strains were observed. All isolates were sensitive to oxacillin, vancomycin and selectrin. 92.8% (103/111) staphylococcus aureus isolates were resistant to at least one antimicrobial. 38.7% (43/111) strains were multi-drug resistant isolates. The resistance rate of isolates in artels (100% (48/48)) was higher than it in farms (87% (55/63)) and the difference was statistically significant (χ(2) = 4.80, P < 0.05). The multi-resistance rate of isolates in artels (54% (26/48)) was higher than it in farms (27% (17/63)) and the difference was also statistically significant (χ(2) = 8.48, P < 0.05). The 111 strains were clustered into 8 types, 6 out of which were consisted of 98% isolates (109/111), and were prevalent in 2 to 9 herds. Every herd had 1 to 4 types, and tend to be comprised by one major type. Most swab isolates were indistinguishable from isolates infecting the mammary gland. There were no relationship between antimicrobial resistance profiles and genotypes of these isolates.

CONCLUSIONThe drug resistance of staphylococcus aureus isolates associated with lactating cows of 5 provinces in China is serious, especially the isolates collected from artels. A few specialized clones were responsible for most of the cases of bovine mastitis in a single herd and some clones might have a broad geographic distribution.