Antibacterial Activity of Zinc Oxide Nanoparticles Against Toxigenic Bacillus cereus and Staphylococcus aureus Isolated from Some Egyptian Food

Antibacterial activities of zinc oxide nanoparticles against two toxigenic bacteria isolated from Egyptian food (Bacillus cereus and Staphylococcus aureus) were investigated in this study. Fifteen samples of five types of sandwiches (Falafel with salad, falafel without salad, bean, sausage and beef luncheon) were purchased from El-Mahla El-Kobra restaurants Tanta, Egypt and investigated for some bacteria species using specific media and incubated for 24-48 hours. The results revealed that bacterial load was highest in falafel with salad sandwich, total coliform and fecal coliform. On the other hand, the contamination was lower in all samples than that in falafel with salad sandwich. The presence of B. cereus was higher in sausage sandwich3 and beef luncheon sandwich3 while S. aureus was low in all samples. Multiplex PCR technique was used to detect the toxin genes (hblC and cytK) in suspected toxic B. cereus strains and sea and sec enterotoxins genes in S. aureus strains. The multiplex PCR amplification allowed rapid detection and identification of enterotoxin genes in food borne bacteria. ZnO nanoparticles with sizes of < 100 nm and concentrations of 100, 200, 300, 400 and 500 μg/ml and nanoparticles-free solutions were used in antimicrobial tests against toxigenic Bacillus cereus and Staphylococcus aureus by agar diffusion method. ZnO nanoparticles showed increasing inhibitory effects on the growth of Bacillus cereus and Staphylococcus aureus as the concentrations of ZnO nanoparticles increased. The MIC of ZnO nanoparticles for Bacillus cereus and Staphylococcus aureus were determined to be < 10 and < 5 μg/ml respectively. Transmission electron microscopy (TEM) was used to characterize the changes of cellular compositions of bacterial cells treated with ZnO nanoparticles and study the mode of action of ZnO NP against Bacillus cereus and Staphylococcus aureus.