Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2011
Publication Date: 3/22/2011
Citation: Xie, Y., He, Y., Irwin, P.L., Jin, Z.T., Shi, X. 2011. Antibacterial activity and mechanism of action of zinc oxide nanoparticles against Campylobacter jejuni. Applied and Environmental Microbiology. 77:2325-2331. Interpretive Summary: The antimicrobial activity and molecular basis of ZnO nanoparticles were investigated on C. jejuni, an important foodborne pathogen and a common cause of bacterial gastroenteritis worldwide. In this study, we found that C. jejuni was extremely sensitive to ZnO nanoparticles; 8-16 fold more sensitive than other foodborne pathogens Salmonella and E. coli O157:H7. The nanoparticles didn’t only stop C. jejuni from growing but killed the cells. After exposure to ZnO nanoparticles, the cells displayed a dramatic change in morphology and certain degree of membrane leakage by scanning electron microscopic and quantitative molecular analyses. Importantly, we provide the first molecular evidence that the antimicrobial mechanism of ZnO nanoparticles is likely due to the induction of oxidative stress in bacteria. The rapid and lethal effect of ZnO nanoparticles on Campylobacter, even at low concentration levels, implies a potential use in food systems to control this and other pathogens. The understanding of the molecular basis of ZnO nanoparticle action in bacteria could lead to the development of more powerful but less toxic antimicrobial nanoparticles for food safety applications.
Technical Abstract: The antibacterial effect of ZnO nanoparticles on Campylobacter jejuni was investigated for cell growth inhibition and inactivation. The results showed that C. jejuni was extremely sensitive to the treatment of ZnO nanoparticles. The minimal inhibitory concentration (MIC) of ZnO nanoparticles to C. jejuni was determined to be 0.05-0.025 mg/ml, which is 8-16 fold lower than that to Salmonella enterica Entertidis and Escherichia coli O157:H7 (0.4 mg/ml). The action of ZnO nanoparticles on C. jejuni was determined to be bactericidal, not bacteriostatic. Scanning electron microscopic examination revealed that the majority of the cells transformed from spiral shapes into coccoid forms after exposure to 0.5 mg/ml ZnO nanoparticles for 16 hrs, which is consistent with the morphological changes of C. jejuni under other stressed conditions. These coccoid cells were found to have a certain level of membrane leakage by ethidium monoazide-quantitative PCR (EMA-qPCR) assay. To address the molecular basis of ZnO nanoparticle action, a large set of genes involved in cell stress response, motility, pathogenesis, and toxin productions were selected for a gene expression study. Reverse transcription-quantitative PCR (RT-qPCR) analysis showed that in response to the treatment of ZnO nanoparticles, the expression levels of two oxidative stress genes (katA and ahpC) and a general stress response gene (dnaK) were increased 52-, 7-, and 17-fold, respectively. These results suggest that the antibacterial mechanism of ZnO nanoparticles is most likely due to the disruption of cell membrane and induction of oxidative stress in Campylobacter.