Antibacterial Effect of ZnO Nanoparticles on Intestinal Bacteria

Introduction: The application of engineered nanoparticles (NPs) for food safety is increasingly being explored.  Zinc oxide (ZnO) NPs are inorganic chemicals with exceptional biocompatibility, non-toxicity and bioactivity characteristics and considered safe for use in the pharmaceutical and medical industries.  However, not much is known about the behavior of such NPs upon ingestion and whether they inhibit natural gut microflora. 

Purpose: The objective of this study was to investigate the effects of ZnO on the intestinal bacteria Escherichia coli, Lactobacillus acidophilus and Bifidobacterium animalis.  

Methods:  ZnO NPs at concentrations of 0, 12, 16, and 20 mM were used in tube dilution tests.  Tryptic soy broth or Lactobacilli MRS broth without NPs and containing NP-free solution were used as controls.  Cells were exposed to the different ZnO NPs concentrations in broth for 24 h, before plating on respective agar medium for each bacterial strain.

Results: At the end of 24 h of exposure, numbers of all three bacterial strains did not significantly differ from those of the controls. Growth of L. acidophilus and B. animalis initially slowed up to 10 h, but their numbers increased to within 1 log CFU/ml or less compared to the control by the end of 24 h.  No significant differences were found in cell reduction among the different concentrations of ZnO NP tested.  

Significance: This study revealed that ZnO NPs had no significant inhibitory effect on E. coli, L. acidophilus and B. animalis.  Further research is ongoing to examine the effect of other engineered NPs on intestinal bacteria and intestinal epithelial cells.