Potential Application of Nanoparticles as Antipathogens - Advanced Materials for Agriculture, Food and Environmental Safety - page 342

12.5.4 Titanium Dioxide Nanoparticles

Titanium dioxide (TiO 2 ) nanoparticles catalyze the killing of bacteria on
illumination by near-UV light. h e generation of active free hydroxyl radi-
cals (OH) by photo excited TiO 2 particles is probably responsible for the
antimicrobial activity. h e use of TiO 2 photocatalysts as an alternate means
of self-disinfecting contaminated surfaces on further development may
provide potent disinfecting solution for prevention of bioi lm formation.
In recent years, visible-light absorbing photocatalysts with Ag/AgBr/TiO 2
have proven to be successful at killing S. aureus and E. coli [33-34], [57].

12.5.5 Zinc Oxide Nanoparticles

h e antimicrobial activity of zinc oxide nanoparticles has been studied
against the food-related bacteria Bacillus subtilis, E. coli and Pseudomonas
l uorescence. h e ZnO NPs could potentially be used as an ef ective anti-
bacterial agent to safely protect agriculture and food from food borne path-
ogens, especially E.coli [58-60]. h ere are also other studies which coni rm
that antimicrobial activity of ZnO nanoparticles could be used against
the food borne bacteria Salmonella typhimurium and Staphylococcus
aureus . h e antibacterial ef ect of zinc oxide (ZnO) nanoparticles
on Campylobacter jejuni was investigated for inhibition and inactivation
of cell growth. h e results showed that C. jejuni was extremely sensitive to
treatment with ZnO nanoparticles. h e MIC of ZnO nanoparticles for C.
jejuni was determined to be 0.05 to 0.025 mg/ml, which is 8- to 16-fold
lower than that for Salmonella enterica, Serovar enteritidis and Escherichia
coli O157:H7 (0.4 mg/ml). h e action of ZnO nanoparticles against C.
jejuni was determined to be bactericidal, not bacteriostatic. Scanning elec-
tron microscopy examination revealed that the majority of the cells trans-
formed from spiral shapes into coccoid forms at er exposure to 0.5 mg/
ml of ZnO nanoparticles for 16 h, which is consistent with the morpho-
logical changes of C. jejuni under other stress conditions. h ese coccoid
cells were found by ethidium monoazide-quantitative PCR (EMA-qPCR)
to have a certain level of membrane leakage. To address the molecular
basis of ZnO nanoparticle action, a large set of genes involved in cell
stress response, motility, pathogenesis, and toxin production were selected
for a gene expression study. Reverse transcription-quantitative PCR
(RT-qPCR) showed that in response to treatment with ZnO nanoparticles,
the expression levels of two oxidative stress genes ( katA and ahpC ) and a
general stress response gene ( dna K ) were increased 52-, 7-, and 17-fold,
respectively. h ese results suggest that the antibacterial mechanism of ZnO