Antimicrobial and cytotoxicity effect of Synthesized Ag-doped ZnO nanoparticles against Listeria monocytogenes isolated from traditional Cheese

Listeriosis (caused by Listeria monocytogenes) is one of the most serious and severe foodborne diseases. The purpose of present study is to investigate the antibacterial, antiinvasion and anti-adhesion effect of synthesized Ag-doped ZnO (ZnO:Ag NPs) nanoparticles against L.monocytogenes isolates. ZnO and ZnO:Ag NPs were synthesized using a chemical method and were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Energy Dispersive X-ray (EDX) and Fourier-transform infrared (FTIR) spectroscopy. Antibacterial assay of nanoparticles towards L. monocytogenes was performed using culture turbidity measurement. The MTT assay was performed for assessing cytotoxicity activity in Caco-۲ cells exposed to L.monocytogenes treated with ۳.۱۲۵, ۶.۲۵, ۱۲.۵, ۲۵, ۵۰ and ۱۰۰ μg /ml concentrations of both ZnO and ZnO:Ag NPs. The adhesion and invasion assays were performed by infecting semiconfluent Caco-۲ cell monolayers grown in ۲۴-well plates. To further confirm, the messenger RNA (mRNA) levels of invasion and adhesion‐associated genes (inlA, hlyA and prfA) of L. monocytogenes were examined using Real-time PCR. Our results show ZnO:Ag NPs have great antibacterial activities against L.monocytogenes isolates. Paper results also indicated exposure of L.monocytogenes isolates treated with all concentration of ZnO:Ag NPs could obviously reduce the viability of Caco-۲ cells. The results of Realtime PCR revealed that the mRNA levels of inlA, hlyA and prfA were dramatically downregulated after the exposure of L.monocytogenes treated with ZnO:Ag NPs compared to ۱۶S rRNA as housekeeping gene. It can therefore be considered that ZnO:Ag NPs should be utilized in medicinal and pharmaceutical applications as credible antibacterial, anti-invasion and anti-adhesion agents.

Keywords:

ZnO , ZnO:Ag NPs , Antibacterial activity , Listeria monocytogenes , MTT Assay , Real-time PCR