Purpose: The objective of this study was to elucidate the effectiveness of PUV irradiation treatment on biofilms formed by E. coli O157:H7 and Listeria monocytogenes on food packaging material and romaine lettuce (Lactuca sativa).
Methods: Overnight cultures of E. coli O157:H7 EDL933 and Listeria monocytogene V7 were diluted in growth media. One milliliter of diluted culture was transferred to the petri dishes containing pieces of romaine lettuce and polyethylene packaging films, 3 x 3 cm in size, and incubated under static conditions at 30 °C for 48 h where the pieces were submerged in media containing the bacterial cultures. The formation of biofilm was confirmed by crystal violet staining. Biofilms were treated with pulsed ultra violet light using a Xenon SteriPulse 3000-XL pulsed UV light system. The samples were placed at distances of 4.5 and 8.8 cm away from the UV strobe, and treated with pulses for either 10 or 20 seconds. Reduction of the biofilm was determined by standard plating procedures following serial dilutions.
Results: The L. monocytogens count of biofilms formed on lettuce surface was reduced 2.1 to 3 log for 10 and 20 second treatments, respectively. While E. coli O157:H7 count was reduced by 2.7 to 4.5 log for 10 and 20 second treatments, respectively. Similar results were observed for biofilm reduction on the polyethylene packaging film surfaces. Our results indicate that PUV has a moderate effect in reducing E. coli O157:H7 and Listeria monocytogenes’ population in biofilms on contact surfaces and fresh produce. It was also found that PUV treatment was more effective in reducing E. coli O157:H7 biofilms as compared to Listeria biofilms.
Significance: PUV light treatment has moderate effect on reducing biofilms formed by E. coli O157:H7 and Listeria monocytogenes on food packaging material and romaine lettuce surfaces. The results of the present study indicate that PUV can be a non-thermal intervention method of choice that can be used for surface decontamination of produce and packaging materials.