G. Zheng
Lincoln University, USA
Title: Biological control of post-harvest contamination of Salmonella in lettuce by using a native strain, Bacillus subtilis LG-7
Biography
Biography: G. Zheng
Abstract
Fresh lettuce and other produce are known to be associated with several recent foodborne outbreaks in the United States. The objectives of this study were to isolate endospore-forming bacteria from lettuce and to use them as the biocontrol agents to reduce and prevent foodborne pathogens from contamination in lettuce. The isolate B. subtilis LG-7a strain was one of the 4 isolates that were relatively potent against the three foodborne pathogens in the agar tests. A cat-tagged B. subtilis LG-7a strain was genetically engineered to facilitate the evaluation of the efficacy of B. subtilis LG-7a in controlling post-harvest Salmonella contamination in lettuce. The efficacy was evaluated respectively at 4 °C, room temperature, and 37 °C. It was found that although the anti-Salmonella cat-tagged B. subtilis LG-7a (cattagged LG-7a) could colonize in/on lettuce stem in the range of 2, 000 CFU per g of stem, it did not inhibit for at least the first day of postharvest the replication of the pathogen spiked on the cut surface of lettuce under both room temperature and 37 °C. However, cat-tagged LG-7a began to show inhibition against the spiked Salmonella after the second day of postharvest under 37°C. Overall, this study suggests that the efficacy of colonized Bacillus bacteria in controlling the post-harvest Salmonella contamination may not be higher than the refrigeration and that the value of the isolates in control pre-harvest pathogen contamination in lettuce may be the focus of the future studyFresh lettuce and other produce are known to be associated with several recent foodborne outbreaks in the United States. The objectives of this study were to isolate endospore-forming bacteria from lettuce and to use them as the biocontrol agents to reduce and prevent foodborne pathogens from contamination in lettuce. The isolate B. subtilis LG-7a strain was one of the 4 isolates that were relatively potent against the three foodborne pathogens in the agar tests. A cat-tagged B. subtilis LG-7a strain was genetically engineered to facilitate the evaluation of the efficacy of B. subtilis LG-7a in controlling post-harvest Salmonella contamination in lettuce. The efficacy was evaluated respectively at 4 °C, room temperature, and 37 °C. It was found that although the anti-Salmonella cat-tagged B. subtilis LG-7a (cattagged LG-7a) could colonize in/on lettuce stem in the range of 2, 000 CFU per g of stem, it did not inhibit for at least the first day of postharvest the replication of the pathogen spiked on the cut surface of lettuce under both room temperature and 37 °C. However, cat-tagged LG-7a began to show inhibition against the spiked Salmonella after the second day of postharvest under 37°C. Overall, this study suggests that the efficacy of colonized Bacillus bacteria in controlling the post-harvest Salmonella contamination may not be higher than the refrigeration and that the value of the isolates in control pre-harvest pathogen contamination in lettuce may be the focus of the future study