Abstract: Several dairy farms discovered mastitis in Shanxi province in 2011. 76 milk samples isolation and identification of bacteria were presented. And Disc diffusion test (K-B method) was used to study the antimicrobial resistance of the main organisms. Results showed that most of isolated organisms were Gram-positive bacteria; Gram-positive cocci and other Gram-positive bacteria were 60.67% and 23.59%, respectively. And the detection rate of pathogens (Streptococcus, Staphylococcus aureus and etc.) and opportunistic pathogen (Streptococcus faecalis, Micrococcus, Klebsiella spp and etc.) were 2.24% to 11.24% and 1.12% to 11.24%, respectively. Streptococcus agalactiae, Streptococcus faecalis and micrococcus had high detection rate, 11.24%, 11.24% and 6.74%, respectively. Drug sensitivity test results showed that all isolated organisms were sensitive to amikacin, norfloxacin and enrofloxacin in 15 drugs. Escherichia coli, Klebsiella spp and coagulase negative Staphylococci had strong resistance to penicillins and β-Lactamaseinhibitors. The resistance rates were 100%. Streptococcus uberis also had resistance to the two kinds of drugs at different degree, 20% to 100%.The resistance rates of Escherichia coli, Klebsiella spp, Streptococcus agalactiae, Streptococcus uberis, and Streptococcus dysgalactiae etc to streptomycin were 100%. And some organisms had resistance to kanamycin, gentamicin, streptomycin, tetracycline, erythromycin, cephalosporin V, sulfamethoxazole compound etc at different degree. The milk samples had serious mixed infections. There is a need to strengthen environmental sanitation management. And the clinical medication should be reasonable and effective.

Key words: clinical mastitis; isolation; antimicrobial susceptibility