Analysis of the tetracycline resistance of Staphylococcus aureus from cow mastitis.

To investigate the tetracycline-resistance of Staphylococcus aureus isolated from cow mastitis,twenty-six S.aureus isolates were tested and determinated for minimum inhibitory concentration(MIC) with Kirby-Bauer(K-B) diffusion method and macrodilution,the effect of active efflux inhibitors of reserpine on MIC was also tested.The results showed that about 27% S.aureus isolates exhibited tetracycline-resistance.The tetracycline-resistance genes of tetM,tetO,tetL and tetK were detected by PCR.Sequence analysis showed that the tetM shared 99.9% sequence identities with transposon Tn916.The existence of tetracycline resistance genes was consistent with the resistant phenotypes,and the tetracycline resistance was mainly mediated by the efflux mechanism.The resistance gene tetK was first detected in S.aureus isolated from cow mastitis in China.