Zinc Oxide and Silver Nanoparticle Effects on Intestinal Bacteria

Introduction: The application of engineered nanoparticles (NPs) for food safety is increasingly being explored. Zinc oxide (ZnO) and silver (Ag) NPs have significant potential for a wide range of applications, including being incorporated into food packaging to improve food safety. However, NPs may also pose potential risks to consumers if they migrate from food packaging to food matrices. In our previous studies, the toxicity of ZnO and Ag NPs on the intestinal bacteria, Escherichia coli, Lactobacillus acidophilus and Bifidobacterium animalis was investigated. Numbers of all three treated cells were within 1 log CFU/ml less than that of the control. However, not much is known about the mode of action of ZnO and Ag NPs on bacterial cells.  

Purpose: The objective of this study was to investigate the mode of action of ZnO and Ag NPs on E. coli, L. acidophilus and B. animalis using multiple analytical tools.

Methods: Multiple analytical tools included scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), UV spectroscopy and confocal fluorescence microscopy.

Results: SEM and TEM images and EDS demonstrated adherence of NPs to the bacterial cells. Morphological changes of some cells were observed, but many remained in normal shapes. UV absorbance results indicated no significant leakage of internal cellular contents due to NPs. Viability of bacterial cells, as assessed by the Live/Dead Bacterial Viability assay, showed that more viable than dead cells was present after treatment with NPs.

Significance: This study revealed that ZnO and Ag NPs have milder inhibitory effects on intestinal bacteria as compared to those on pathogenic microorganisms that have been previously reported. Further research is required to investigate the exact mechanisms of how the NPs affect bacterial cells.