|YAN, RUIXIANG - TIANJIN UNIVERSITY OF SCIENCE AND TECHNOLOGY|
Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2016
Publication Date: 1/26/2017
Citation: Yan, R., Liu, Y., Gurtler, J., Fan, X. 2017. Sensitivity of pathogenic and attenuated E. coli O157:H7 strains to ultraviolet-C light as assessed by conventional plating methods and ethidium monoazide-PCR. Journal of Food Safety. doi: 10.1111/jfs.12346.
Interpretive Summary: Ultraviolet(UV)light, as one of the postharvest interventions, is simple to implement and inexpensive for commercial applications. To conduct trails on a large scale or at a commericial setting, non-pathogenic/attenuated surrogates of pathogenic bacteria should be used due to the difficulty for containment and post-treatment decontamination of equipment and the environment. This study was conducted to evaluate the UV-C sensitivity of various pathogenic and nonpathogenic E. coli O157:H7, and to investigate the mechanism of UV-C disinfection using a PCR method. Results showed that the attenuated/non-pathogenic strains of E. coli on average had similar sensitivities as the pathogenic strains, and therefore could serve as surrogates. Futhermore, cell membrane was not affected by moderate doses of UV-C treatments even though the bacteria were not cultivable. The information will be useful for researchers to conduct scale-up trails, and to optimize the UV-C technology for the purpose of microbial safety enhancement.
Technical Abstract: In this study, the UV-C sensitivity of six pathogenic E. coli O157:H7 strains associated with recent outbreaks of foodborne illnesses and four attenuated E. coli O157:H7 strains was investigated. Futhermore, the mechanism of UV-C impact on two pathogenic E. coli strains with different UV-C sensitivity was evaluated using real time PCR with and without ethidium monoazide (EMA) pretreatment. Results showed that RM6535, a strain associated with the 2006 lettuce outbreak, was the most sensitive among the pathogenic strains. The UV-C inhibition on the PCR amplification of DNA correlated well with UV-C close, as indicated by the cycle threshold (Ct), regardless of EMA pretreatment. The Ct values increased linearly with increasing UV-C doses in the 0-203 mJ/cm2 dose range. The difference in UV-C sensitivity between RM6535 and EDL933 was also reflected by increases in Ct values. Quantification of viable cells using EMA-PCR resulted in serious overestimations compared to the conventional plating methods. EMA-PCR analysis also indicated that the cell membrane was affected only at high doses when UV-C inactivated more than 6 log CFU of bacteria. Overall, our results suggest that E. coli strains have various sensitivities to UV-C and that PCR is a useful tool to assess DNA damage caused by UV-C.