Abstract
The aim of the studies was analysis of resistance of Staphylococcus aureus isolates from bovine mastitis in eastern part of Poland to a set of 20 antibiotics and three alternative agents: lysostaphin, nisin and polymyxin B. Eighty-six out of 123 examined isolates were susceptible to all of 20 tested antibiotics (70%). The highest percentage of resistance was observed in the case of β-lactam antibiotics: amoxicillin (n=22, 17.9%), ampicillin (n=28, 22.8%) and penicillin (n=29, 23.6%) and streptomycin (n=13; 10.6%). Twenty-five out of penicillin resistant strains were found to carry blaZ gene coding for β-lactamases. Two strains were found to be mecA positive and few strains were classified as Multi Drug Resistant (MDR), one of them was simultaneously resistant to six antibiotics. All strains, resistant to at least one antibiotic (n=37) and two control strains, were susceptible to lysostaphin with MIC values of: 0.008–0.5 µg/ml(susceptibility breakpoint 32 µg/ml). Twenty-one (54%) isolates were susceptible to nisin. The MIC value of this agent for 17 (44%) strains was 51.2 µg/ml and was not much higher than susceptibility breakpoint value (32 µg/ml). The polymyxin B was able to inhibit the growth of the strains only at high level of concentration (32–128 µg/ml). The presented results confirmed observed worldwide problem of spreading antibiotic resistance among staphylococci isolated from bovine mastitis, on the other hand, we have indicated high level of bactericidal activity of nisin and especially lysostaphin.
