Abstract: To identify serotype distribution of bovine Streptococcus agalactiae and its drug resistance to common antibiotics, so that the correct antibiotics was applied during clinical therapy, 78 local strains of Streptococcus agalactiae were isolated from milk samples of dairy cow with clinical mastitis throughout the country. We prepared antigens for precipitation reaction and hyperimmune serum antibodies of 6 standard serotype Streptococcus agalactiae strains, then 78 local strains of Streptococcus agalactiae were identified by ring precipitation test and antibiotic resistance were analyzed. In China, the predominant serotype of Streptococcus agalactiae in bovine mastitis were X-type (60.26%),Ⅲ-type (10.26%), R-type (7.69%), Ⅱ-type (7.69%) andⅠb-type (5.13%) respectively. However, Ⅰa-type was not found. At present, Streptococcus agalactiae were sensitive to most clinical used antibiotics. The stronger inhibitory effect of the drugs to the bacteria were Cefazolin, Cefotaxime, Amikacin, Kanamycin, Gentamicin, Tetracycline, Doxycycline, Florfenicol, Polymyxin B, Ciprofloxacin, Norfloxacin and Ceftazidime/Clavulanic acid. In contrast, Streptococcus agalactiae could resist the effect of Penicillin G, Ampicillin, Streptomycin, Enrofloxacin, Amoxicillin/Clavulanic acid and Cotrimoxazole, the resistance rate of the bacteria to these antibiotics was about 50% to 100%. This study is significant for further development of effective drugs, vaccines and clinical therapy.

Key words: bovine mastitis; Streptococcus agalactiae; serotype; antibiotics; sensitive