Antibiotic Sensitivity of Streptococci and Enterococci from Mastitis in Cows in 2010-2011

The aim of the study was to establish the in vitro sensitivity of S. agalactiae (126 strains), S. dysgalactiae (82 strains), S. uberis (419 strains), and Enterococcus sp. (136 strains) isolated from mastitis in cows to 13 antibiotics. Bacteriological examinations of quarter milk samples were conducted with the recommendations of the IDF. Sensitivity to antibiotics was tested by disk diffusion method in Mueller-Hinton agar and performed according to CLSI guidelines. It was found that S. agalactiae strains were the most sensitive to bacitracin (97.6%), cefapirin (96.3%), and amoxicillin (93.7%), and resistant to neomycin (89.7%), tetracycline (49.2%), and cloxacillin (38.9%). S. dysgalactiae showed the highest sensitivity to bacitracin (100%), cefapirin (100%), amoxicillin (97.6%), cephalexin (97.6%), cefoperazone (93.9%), and resistance to neomycin (61.0%) and tetracycline (53.7%). S. uberis strains were mainly sensitive to cefapirin (98.9%), bacitracin (98.8%), cefquinome (97.6%), amoxicillin (97.4%) and resistant to neomycin (93.3%), tetracycline (35.3%) and lincomycin (22.4%). Enterococcus sp. showed the high sensitivity to amoxicillin (83.8%) and bacitracin (82.4%), and resistance to cloxacillin (76.5%), cephalexin (58.1%), lincomycin (55.9%), neomycin (53.7%), penicillin (48.5%), and tetracycline (36.0%). In conclusion, strains of S. dysgalactiae were more sensitive to tested antibiotics than S. agalactiae, S. uberis, and especially Enterococcus sp. Only 8.8% of S. agalactiae, 4.3% of S. dysgalactiae, 4.3% of S. uberis, and 4.4% of Enterococcus sp. strains were sensitive to all tested antibiotics. The largest diversity in the resistance was found in Enterococcus sp.