Recovery of Foodborne Microorganisms from Potentially Lethal Radiation Damage

Abstract

A two-stage recovery protocol was examined for microorganisms following gamma irradiation in phosphate buffer at 0 degrees C. In the first stage, survivors were recovered on basal yeast extract agar and held at various temperatures suboptimal for their growth for 20 h (resuscitation protocol). In the second stage the survivors were incubated for an additional 24 h, but in this case at their optimum temperature for growth. Controls consisted of survivors which were not subjected to the resuscitation protocol (direct incubation at their optimum growth temperature). The ratio of survivors enumerated with and without the resuscitation protocol (control) at each specified temperature was used to formulate a recovery factor(RF). An RF was determined for each treatment dose. Results of this study indicated that the number of Escherichia coli, Salmonella serotype typhimurium and Brochothrix thermosphacta survivors increased following a resuscitation protocol (RF> 2.0). Overall, optimum resuscitation temperatures ranged from 14 to 22 degrees C. The extent of recovery also appeared dose dependent, with larger treatment doses giving rise to a higher RF. S. serotype typhimurium irradiated at 1.5 kGy exhibited the highest RF, 161, when resuscitated at 22 degrees C. Listeria monocytogenes, Yersinia enterocolitica, Staphylococcus aureus, Aeromonas hydrophila and Saccharomyces cerevisiae exhibited an RF < 2.0 regardless of resuscitation temperature. Results of this study indicated that the use of suboptimal holding temperatures as part of a recovery protocol may have advantages, especially with respect to the enumeration of E. coli and salmonellae survivors in irradiated foods such as poultry.

Attenuation of 10MeV electron beam energy to achieve low doses does not affect Salmonella spp. inactivation kinetics

“…The average D 10 values for the Salmonella cocktail were slightly greater than for Salmonella 4,[5],12:i:-alone, indicating that the cocktail was more resistant to eBeam irradiation than the Salmonella 4, [5],12:i:-serovar alone (Table 1). This is congruent with other studies showing strain/serovar variability in terms of ionizing radiation susceptibility (Lucht et al, 1998). In addition, our results showed there was consistent variation (standard deviations in Table 1) within the three individual trials for both the non-attenuated 10 MeV eBeam irradiations (Figs.…”

Physicochemical and functional properties of shell eggs following electron beam irradiation

“…Furthermore, sub-lethal dosages of irradiation (ie 43 kGy) can cause partial damage to bacteria, which will change the nutrient and physical requirements for repair and growth when stored at 4°C. 29 A lack of penetration into a dense medium such as shell eggs by EBI 27 may explain the less than absolute bactericidal effect, which contributed to viable bacterial counts observed in all irradiated eggs. Nevertheless, a 4 kGy dosage was effective at lowering all bacterial counts to an undetected level of <1 log immediately after irradiation.…”

Effects of gamma irradiation on the survival of Pseudomonas fluorescens inoculated on romaine lettuce and baby spinach

“…Similarly, sub-lethal injury of microbes in response to gammaradiation treatment as well as other physical, chemical, nutritional or environmental stresses have been previously reported (Lucht, Blank, & Borsa, 1998;Moosekian, Jeong, & Ryser, 2014). In a research study on the recovery of food-borne pathogens from lethal radiation damage, it was documented that incubating radiationtreated bacteria at sub-optimal temperatures was more effective in recovering injured cells than was incubating at optimal growth temperature (Lucht et al 1998). In that study, the researchers noted that radiation exposure of P. fluorescens at 0.15 kGy followed by incubation at 22 C could result in recovery of gamma-irradiated cells.…”