Microbial radiosensitization using combined treatments of essential oils and irradiation- part B: Comparison between gamma-ray and X-ray at different dose rates

Authors: SHANKAR, S - Institut National De La Recherche Scientifique (INRS); Follett, Peter; AYARI, S - Institut National De La Recherche Scientifique (INRS); HOSSAIN, F - Institut National De La Recherche Scientifique (INRS); SALMIERI, S - Institut National De La Recherche Scientifique (INRS); LACROIX, M - Institut National De La Recherche Scientifique (INRS)

Submitted to: Microbial Pathogenesis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2020
Publication Date: 3/6/2020
Citation: Shankar, S., Follett, P.A., Ayari, S., Hossain, F., Salmieri, S., Lacroix, M. 2020. Microbial radiosensitization using combined treatments of essential oils and irradiation- part B: Comparison between gamma-ray and X-ray at different dose rates. Microbial Pathogenesis. 143. Article 104118. https://doi.org/10.1016/j.micpath.2020.104118.
DOI: https://doi.org/10.1016/j.micpath.2020.104118

Interpretive Summary: Plant essential oils vapor can have microbicidal effects. Irradiation also can control bacterial and fungal pathogens but there are lingering questions about dose rate. A mixture of oregano/thyme was tested against Aspergillus niger, Bacillus cereus, and Paenibacillus amylolyticus in rice with and without irradiation treatment at different dose rates. In all cases, irradiation plus fumigation with the oregano and thyme EO mixture showed increased efficacy compared with irradiation alone. There was no consistent positive or negative relationship between irradiation dose rate and relative sensitivity.

Technical Abstract: Stored rice and rice products are prone to contamination by pathogenic fungi and bacteria such as Aspergillus niger, Bacillus cereus, and Paenibacillus amylolyticus. Treatment with antimicrobial essential oils (EOs) and irradiation are options to control spoilage organisms. Microbial samples in rice with or without fumigation with an Oregano and Thyme EO mixture were irradiated at 0.5, 0.75, 1.0, 1.5, 2.0 and 2.5 kGy for calculation of a D10 value. The relative sensitivity was calculated as the ratio of D10 values for the irradiation plus Oregano and Thyme EO combination and irradiation alone treatments. In all cases, irradiation plus fumigation with the oregano and thyme EO mixture showed increased efficacy compared with irradiation alone. The relative sensitivity of '-ray irradiation against A. niger was 1.22, 1.33, and 1.24 for radiation dose rates of 10.44, 4.445, and 0.085 kGy/h, respectively, however against B. cereus it was 1.28, 1.45, and 1.49, and against P. amylolyticua it was 1.35, 1.33, and 1.38, for respective '-ray irradiation dose rates. The relative sensitivity of X-ray irradiation against A. niger, B. cereus, and P. amylolyticus was 1.63, 1.21, and 1.31, respectively, at the X-ray dose rate of 0.76 kGy/h. The results showed that the relative sensitivity of '-ray irradiation was higher against the two bacteria than the fungus, whereas X-ray showed higher against the fungus was higher than the two bacteria. There was no consistent positive or negative relationship between dose rate and relative sensitivity. The results demonstrated the potential of a Oregano and Thyme EOs mixture as an antimicrobial agent and its efficacy to increase the radiosensitivity of A. niger, B. cereus, and P. amylolyticus during '-ray or X-ray irradiation treatments.