Antimicrobial Susceptibility of Bacteria Isolated from Cows with Mastitis in 2006-2007

The purpose of the study was determining the in vitro sensitivity of Streptococcus agalactiae, other Streptococcus sp., Staphylococcus aureus, coagulase-negative staphylococci, Escherichia coli, and Arcanobacterium pyogenes strains to antibiotics commonly used in veterinary praxis. These pathogens were isolated from cows with clinical or subclinical mastitis in 2006–2007. The activity of 10–14 antibiotics to each bacterial species was examined. The sensitivity was tested by disk diffusion method and performed according to CLSI guidelines in Mueller-Hinton agar. Streptococcus agalactiae strains were mostly sensitive to amoxicillin (93.6%), cefquinom (96%), cefapirin (94.1%), cefoperazone (88.9%, bacitracin (87.1%), and cephalexin (79%). Other streptococci were most susceptible to amoxicillin (91.4%), cefquinom (84.1%), bacitracin (89%), and cephalexin (79.7%). Amoxicillin/clavulanic acid (97.4%), cloxacillin (90%), cefquinom (92.9%), cephalexin (90.5%), and bacitracin (88.6%) were the most active against Staphylococcus aureus. Coagulase-negative staphylococci were sensitive to amoxicillin/clavulanic acid (100%), cefquinom (89.2%), cephalexin (89.3%), bacitracin (86,.1%), rifaximin (86.8%), and cefapirin (86.5%). Norfloxacin (85.1%), enrofloxacin (83.9%), and marbofloxacin (84.4%) were active against Gram-negative bacilli. Only amoxicillin (87.1%) from ten analysed antibiotics exhibited very high activity against Arcanobacterium pyogenes.