Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2005
Publication Date: 7/20/2005
Citation: Niemira, B.A., Solomon, E.B. 2005. Inactivation of planktonic and biofilm-associated salmonella by ionizing radiation. Institute of Food Technologists Annual Meeting, July 17-20, 2005, New Orleans, LA. p. 108-5.
Technical Abstract: Biofilm-associated bacteria have been demonstrated to be more resistant to antimicrobial treatments compared to their planktonic counterparts. Far higher concentrations of chemical sanitizers such as chlorine, trisodium phosphate, and iodine are required to eliminate biofilm-associated cells. Ionizing radiation has been used to inactivate Salmonella on a variety of foods and food contact surfaces, but the efficacy of the process against biofilm-associated cells is not well documented. The radiation sensitivity of three isolates of Salmonella under planktonic or biofilm conditions were determined. Cultures were grown in tryptic soy broth and biofilms were allowed to form on sterile glass slides. The broth and biofilm cultures were irradiated to doses of 0.0 (control), 0.5, 1.0, 1.5, 2.0 and 2.5 kGy. Biofilm-associated cells of S. Stanley and S. Enteritidis were significantly more sensitive to ionizing radiation than their planktonic counterparts. The D10 values of S. Anatum were not significantly (P<0.05) different for biofilm-associated (0.645 kGy) and planktonic cells (0.677 kGy). In contrast, the biofilm-associated cells of S. Stanley were significantly more sensitive to ionizing radiation than respective planktonic cells, with D10 values 0.531 and 0.591 kGy, respectively. D10 values of S. Enteritidis were similarly reduced for biofilm-associated (0.436 kGy) vs. planktonic (0.535 kGy) cells. The antimicrobial efficacy of ionizing radiation is therefore preserved or enhanced when treating biofilm-associated bacteria. Live/Dead staining coupled with confocal microscopy and a novel digital image analysis technique indicated that irradiation eliminated Salmonella at similar rates throughout the biofilm. These results suggest that the biofilm habitat exerts a complex and isolate-dependent influence on the efficacy of ionizing radiation.