Effect of zinc oxide and silver nanoparticles on intestinal bacteria
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In this study, the effects of zinc oxide (ZnO) and silver (Ag) nanoparticles (NPs) on the intestinal bacteria, Escherichia coli, Lactobacillus acidophilus, and Bifidobacterium animalis were investigated. All three bacterial strains were inoculated into tryptic soy broth (TSB) or Lactobacilli MRS broth media containing different concentrations of ZnO (0, 12, 16, 20 mM) and Ag (0, 1.8, 2.7, 4.6 mM) NPs and 1% of NP-free solution and incubated at 37 oC for 24 h. The presence and characterization of ZnO and Ag NPs on bacterial cells were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). UV-visible absorbance and the Live/Dead Bacterial Viability assay were performed to assess membrane leakage and viability of bacterial cells before and after treatment with the NPs. For all bacteria, for up to 12 h of incubation, the numbers of treated cells were within 1 log CFU/mL less than that of the control. Morphological changes of bacterial cells were observed, but many cells remained in normal shapes. Results of UV-visible spectroscopy showed that only a small amount of internal cellular contents were leaked due to the NPs. Also, more live than dead cells were observed after exposure to the NPs. Results indicate that ZnO and Ag NPs have very mild inhibitory effects on intestinal bacteria.