| Three foodborne pathogens were tested for their resistance to Ultraviolet (UV) light on different media/surfaces, for their ability to reactivate under light or dark conditions, and for their resistance to sanitizers and UV light on biofilms on stainless steel surface. When inoculated in peptone water, stainless steel or chicken meat and exposed to 150–1000 μW/cm 2, a dose response was obtained, depending on pathogen type and medium. Salmonella Typhimurium was more resistant than E. coli O157: H7, and Listeria monocytogenes to UV light, in peptone water, but Listeria monocytogenes and Salmonella Typhimurium were more resistant when treated on stainless steel (SS) chips. None of the pathogens were reduced by more than 1.3 logs when inoculated on chicken meat or skin.; When suspensions of the three pathogens were exposed to 300 and 1500 J/m2 UV, they were activated either in dark or under fluorescent light for one hour. Greater effect of UV was noted on E. coli O157:H7 and Listeria monocytogenes than on Salmonella Typhimurium. At 1500 J/m2, no E. coli O157:H7 or Listeria monocytogenes cells were recovered, whereas a strong dark repair was observed for Salmonella Typhimurium. Regardless of pathogen, cross-linked genomic DNA was increased with increased dose but reactivated as the treated cells were repaired.; Biofilms of the pathogens on stainless steel surface were prepared by incubation chips in tryptic soy broth with pathogen cells for 3 and 6 days, followed by washing with sterile peptone water. Chips were treated with UV light, chlorine, quaternary ammonium (quats), and peroxyacetic acid for 1 min. UV light effectively reduced all biofilms of pathogens. Regardless of pathogen type, bacterial counts were higher on 6-day rather than 3-day biofilms. No apparent difference in sanitizing efficacy was observed among biofilms at 10 and 30 ppm. No pathogens were isolated form biofilms treated with the sanitizers at 50 ppm, except on 6-day biofilms of Listeria monocytogenes at 21°C and Salmonella Typhimurium at 35°C treated with quats.; Based on conditions of this study, Salmonella Typhimurium was shown to be more resistant to UV than Listeria monocytogenes or E. coli O157:H7, UV is not an effective treatment on chicken meat or skin, and cross-linked genomic DNA increased with UV dose but disappeared when cells were repaired by dark activation. Common sanitizers used at 50 ppm effectively inactivated 3-day biofilms, but were not effective against 6-day Listeria monocytogenes and Salmonella Typhimurium biofilms. |
