In vitro antibacterial effects of zinc oxide nanoparticles on multiple drug-resistant strains of Staphylococcus aureus and Escherichia coli: An alternative approach for antibacterial therapy of mastitis in sheep

Aim: The aim of the study was to evaluate the antibacterial effects of zinc oxide nanoparticles (ZnO-NPs) and its possible alternative use for the treatment for mastitis in sheep and to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of ZnO-NPs against multidrug-resistant Staphylococcus aureus and Escherichia coli strains isolated from subclinical mastitis cases in sheep. Materials and Methods: A total of 50 pooled milk samples were collected from ewes with subclinical mastitis. Milk samples were cultured using standard laboratory techniques, and multidrug-resistant bacterial strains were determined using the Kirby-Bauer disk diffusion method. The MIC and MBC of ZnO-NPs were determined against isolated multidrug-resistant S. aureus and E. coli strains using microwell dilution method. Results: A total of 43 different bacterial isolates were recovered from milk samples of ewes affected with subclinical mastitis. Isolated strains of S. aureus and E. coli were found resistant to three or more common antibacterial agents and were used to determine the MIC and MBC of ZnO-NPs. The MIC and MBC values of ZnO-NPs were significantly lower for S. aureus than that for E. coli. The MIC and MBC of ZnO-NPs against S. aureus were 3.9 µg/ml and 7.81 µg/ml, respectively, while for E. coli, the MIC and MBC of ZnO-NPs were 31.25 µg/ml and 62.5 µg/ml, respectively. Conclusion: Results of this study indicate the potential antibacterial effects of ZnO-NPs against multidrug-resistant S. aureus and E. coli isolated from ovine subclinical mastitis at concentrations of 3.9 µg/ml and 31.25 µg/ml, respectively.