PREVALENCE OF GRAM POSITIVE BACTERIA IN COW MASTITIS AND THEIR SUSCEPTIBILITY TO BETA-LACTAM ANTIBIOTICS

The aim of this study was to investigate the prevalence of gram-positive bacteria causing cow mastitis in cows and determine their susceptibility to beta-lactam antibiotics. Eight hundred and seventy one isolated gram-positive bacterial strains belonged to Staphylococcus (n=506), Streptococcus (n=196) and Enterococcus (n=169) genera from sub-clinical and clinical cases of bovine mastitis in Lithuania were investigated. The most common causative agents of udder disease included: S. epidermidis (n=176), S. aureus (n=166), S. agalactiae (n=128), and E. hirae/durans complex (n=136). Isolates were analysed for their susceptibility to several beta-lactam antimicrobial agents: penicillin, ampicillin, amoxicillin, cephalothin, cephalexin, amoxicillin + clavulanate. The susceptibility patterns were studied by Agar Disk Diffusion method (ADDM). S. aureus showed the highest level of resistance to amoxicillin (81.7%), penicillin (81.6%) and ampicillin (83.2 %). The corresponding values for cuagulase-negative staphylococci (CNS) strains were 59.5 %, 52.0 % and 50.8 % against penicillin, ampicillin and amoxicillin, respectively. Streptococcus spp. strains mostly were resistant to amoxicillin (31.6%), Enterococcus spp.- to penicillin (28.3 %), ampicillin (21.8 %), amoxicillin (37.8 %) and amoxicillin + clavulanate (31.7 %). The susceptibility of our tested mastitis pathogens to ampicillin and penicillin highly correlated r=0.87. In comparison with other antibiotics amoxicillin and clavulanic acid combination was the most effective (p<0.05) in vitro against all tested gram-positive bacteria. However, S. aureus strains in 41.5 % of cases demonstrated resistance to this combination.