Abstract

Abstract
Bovine mastitis is one of the most complex and costly diseases in dairy farms leading to bacteriological changes in milk affects the quality and quantity of milk. Therefore, a total of 200 mastitic cow’s milk samples from individual lactating cow from different dairy farms in El-Beheria Governorates were collected. The obtained results revealed that Staph. aureus, CNS and E.coli were detected in cow’s mastitic milk at incidence rate 33, 21 and 29%, respectively. Serotyping of ten E.coli isolates revealed presence of O125, O111, O114 and O146. Regarding to antibiotic sensitivity, both Staph. aureus and CNS showed resistance to penicillin 90 and 76.7% respectively while Staph. aureus showed sensitivity to erythromycin (86.7%) and CNS showed sensitivity to gentamycin (90%); E.coli showed resistance to tetracycline (86.7%) and sensitivity to ciprofloxacin (86.7%). Multi-antibiotic resistances (MAR) index of all three isolates were above 0.2. Virulence gene IcaD gene found in all examined Staph. aureus and two samples of CNS, while mecA were found in two samples of each Staph. aureus and CNS. Moreover, tetA and Sul1 were found in 100% of examined E.coli isolates. Characterization of ZnO NPs were done using Ultraviolet-Visible (UV-Vis) Spectroscopy, X-ray diffraction pattern (XRD), SEM, and TEM. The result of anti-bacterial activity of Zn ONPs against Staph. aureus, CNS and E.coli in vitro revealed that ZnO NPs have more antibacterial action with staphylococci species when compared to E.coli. In addition, Minimum Inhibitory Concentration (MIC) of ZnO-NPs against CPS, CNS and E.coli were 6.25, 6.25 and 12.5 µg /ml, respectively. The effect of different concentrations of ZnO NPs on the growth of Staph. aureus, CNS and E.coli was measured and the antibacterial activity of ZnO NPs increased with increasing concentration in vitro.

Key words: Key words: Staph. aureus, CNS, E.coli, antibiotic sensitivity, virulence genes, ZnO nanoparticle, MIC , MAR index, SEM, TEM.