Sensitivity of pathogenic and attenuated E. coli O157:H7 strains to ultraviolet‐C light as assessed by conventional plating methods and ethidium monoazide‐PCR

Abstract

AbstractThe UV‐C sensitivity of six pathogenic Escherichia coli O157:H7 strains associated with recent outbreaks of foodborne illnesses and five attenuated/nonpathogenic E. coli O157:H7 strains was investigated using conventional plating method, and real time PCR with and without ethidium monoazide (EMA) pretreatment. Results showed that the nonpathogenic/attenuated E. coli ATCC 25922, 6980‐2, and 6982‐2 had more or similar resistance to UV‐C compared to the pathogenic strains. The UV‐C inhibition on the PCR amplification of DNA correlated well with UV‐C dose, as indicated by the cycle threshold (Ct), regardless of EMA pretreatment. The Ct values increased linearly with increasing UV‐C doses. Cell membrane was damaged only at high doses when UV‐C inactivated more than 6 log CFU of bacteria. Overall, our results suggest that E. coli strains have different sensitivities to UV‐C and that EMA‐PCR is a useful tool to assess cell damage caused by UV‐C.Practical applicationsUltraviolet (UV) light, as one of the postharvest interventions, is simple to implement and inexpensive for commercial applications. To conduct trials on a large scale or at a commercial setting, nonpathogenic/attenuated surrogates of pathogenic bacteria should be used, due to the difficulty for containment and post‐treatment decontamination of equipment and the environment. We demonstrated the variations in UV‐C sensitivity among pathogenic and nonpathogenic E. coli strains. Three attenuated/nonpathogenic strains of E. coli had similar sensitivities as the pathogenic strains, and therefore, could serve as surrogates. Furthermore, 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 trials, and to optimize UV‐C technology for microbial safety enhancement.