Zinc bacitracin is widely used in Italian rabbit farms to control both Epizootic Rabbit Enteropathy (ERE) and clostridiosis, and field results demonstrate useful activity. Nevertheless, data regarding the in vitro efficacy of zinc bacitracin against clostridia of rabbit origin are not available. In this study, the minimal inhibitory concentrations (MICs) of zinc bacitracin were evaluated in 123 C. perfringens strains isolated from rabbits in Italian fattening units. The agar dilution method was performed in Brucella Agar supplemented with laked sheep blood, haemin and vitamin K1, as recommended in NCCLS document M11-A6. Most strains (94.3%) had low MIC values (£ 0.5 mg/ml), and a few strains (4%) were inhibited by a concentration of 1 mg/ml. Two isolates (1.6%) had a MIC value of 16mg/ml. The MIC values of ATCC reference strains showed a good fit between each batch. MIC required to inhibit the 90% of organisms was 0.5 mg/ml and the presence of only two strains with MIC=16 mg/ml revealed the susceptibility to zinc bacitracin of Italian isolates of C. perfringens from rabbit and the absence of acquired resistance.
Zinc bacitracin; Clostridium perfringens; minimum inhibitory concentration (MIC); rabbit