Radiation sensitivity of planktonic and biofilm-associated Shigella spp. and Aeromonas spp. on food and food-contact surfaces

Although ionising radiation has been shown to kill human pathogens Shigella spp. and Aeromonas spp. on various food products, there is lack of information regarding the relative efficacy of gamma radiation against their free-living planktonic and biofilm-associated cells. The radiation sensitivity (D-10 values) of planktonic, glass-and carrot-associated biofilm cells of Shigella spp. and Aeromonas spp. was determined by forming biofilms on sterile glass and carrot surfaces, incubated at 37 degrees C (Shigella spp.) and 30 degrees C (Aeromonas spp.) for 48 h. No significant difference in the D-10 values of planktonic and glass-associated biofilm cells of Shigella spp. and Aeromonas spp. was observed. However, significant increase in the D-10 values of carrot-associated biofilm cells as compared to planktonic and glass-associated biofilm cells of Shigella spp. and A. hydrophila A331 was observed, whereas A. salmonicida Y567 showed insignificant difference. SEM analysis further validated the formation of biofilm on the carrot and glass surfaces. The antimicrobial effectiveness of ionising radiation against both Shigella spp. and Aeromonas spp. is affected by growth form, strain and nature of attachment surface.