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The overall goal of this proposed study is to determine the efficacy of UV light against Listeria monocytogenes in food systems. In order to validate the overall goal of this study researchers hypothesize that exposure of food systems to UV light will reduce surviving populations of Listeria monocytogenes. <P>To accomplish the overall goal of this project the specific objectives of our proposed study are: 1. Determine the D-values of Listeria Monocytogenes strains (grown at 35 and 4 C) in peptone water and meat extract. LM strains will be inoculated into laboratory media and meat extract and exposed to UV for varying times to determine 90% reduction in bacterial populations. 2. To evaluate the disinfecting efficiency of high and low intensities of UV on log and stationary phase Listeria Monocytogenes grown at two different temperatures. LM will be grown and harvested at log and stationary phases, exposed to low and high intensities by varying the distance from the UV source, and survival populations will be determined in laboratory media and meat extract. 3. Determine the efficacy of UV light against Listeria monocytogenes in Ready-To-Eat poultry products. LM inoculated RTE poultry products will be exposed to predetermined time and UV intensity combinations as optimized by objective 1 and 2; survival populations will be enumerated to evaluate efficacy in food systems. <P>Expected Outcomes: The results from this study can show possible reductions in the survival populations of Listeria monocytogenes in laboratory media, meat extract, and on RTE poultry products. Also, results will be able to demonstrate an ideal time of exposure to UV and intensity of UV combination to attain maximum reductions of the pathogen without adversely affecting quality parameters such as oxidation and color of the products.
Non-Technical Summary: Several factors affect the growth of Listeria monocytogenes (LM) in ready-to-eat (RTE) meat and poultry products including temperature, pH, water activity and microbial competition. In comparison to other pathogenic organisms, LM can grow at very low water activity. Therefore, ready-to-eat meat products could be excellent environments for this organism. The ability of LM to grow at low temperatures, low water activity, and a wide pH range, while most competing organisms cannot, allows for easy survival and proliferation of this organism on RTE products. Most cases of listeriosis are sporadic. However, recently there have been more outbreaks associated with products such as deli meats and frankfurters. Recalls are costly to the food industry because of product loss and loss of customer confidence in certain products and processors involved in the recalls. Contamination of RTE products with LM usually occurs as a result of handling of meat products following cooking and during repackaging. For example, after cooking, casings are removed from RTE meat items such as hot dogs and deli meats are sliced prior to packaging. This coupled with the long shelf life of such RTE meat and poultry products and the ability of LM to grow under refrigerated conditions makes it a pathogen of public health concern. Due to these above mentioned concerns and the potential of developing new technologies to control foodborne pathogens, in this proposal UV radiations will be evaluated to inhibit/ eliminate LM on RTE meat and poultry products. The first phase of this proposal will be to evaluate the efficacy of UV radiations to reduce populations of LM in laboratory media and meat extract and develop D-values. D-values will help in providing information about the susceptibility of this pathogen to UV radiations and set parameter (time and intensity combinations) for the second phase. In the second phase of this study, the efficacy of UV radiation to reduce LM on surfaces of RTE meat and poultry products will be evaluated. Results from this study will be used to develop future studies on the mechanism by which the bacteria are inhibited/ reduced and the impact of prior exposure of LM to other environmental stressors like low temperatures and pH on the microbicidal effects of UV radiation in addition to impact on quality parameters of poultry products. <P> Approach: A panel of 10 UV bulbs (254nm) is hung in a metal framed box with sides made of plexi-glass covered. Listeria monocytogenes serotypes 3a, 4b and 4c will be used in this study. A loop of frozen bacterial culture will be inoculated in brain heart infusion broth for 24h and incubated at 35C. Before using the cultures for any experiment, the cultures will be grown in fresh BHI tubes for two generations. Growth curves of individual serotypes will be obtained at 35 and 4C to determine the log and stationary phase. Bacterial suspensions of each serotype will be prepared separately by centrifuging 20 mL BHI tubes with bacteria for 10 min at 5000 x g, the supernatant will be decanted. The pellet will be resuspended in peptone water (PW), centrifuged again. Bacterial count of the suspension will be enumerated by serially diluting and spread plating 1 mL of suspension. Preparation and inoculation of meat extract (ME): Ground chicken breast meat will be added to PW (1:1) and homogenized for 1 min. The final supernatant will be sterilized and collected in a sterile flask and stored at 4C. Bacterial pellet obtained as stated above will be resuspended with ME. Bacterial count will be enumerated by spread plating. Bacterial suspensions (10mL) in ME and PW at log and stationary phase grown at 35 and 4C will be placed in separate 10cm diameter sterile petri dishes for irradiation. All suspensions will be exposed to UV light of 254 nm at various intensities for 10,30,50,70,90 and 110s. Intensities will be changed by adjusting the height of the UV lamps in the chamber. After exposure for the set period; 1 mL of the exposed suspension will be serially diluted in 9 mL PW and spiral plated. Both sets will be incubated for 24h at 35C and colonies counted. Cooked grilled chicken breast (CB), fully cooked chicken sausage(CS), chicken breast breaded patties (BP) will be used for this experiment. LM 3a,4b and 4c cultures grown at stationary phase will be inoculated on the products at high and low concentration. Bacteria will be introduced on both surfaces of CB and BP. LM in BHI broth will be inoculated on one side of the sample and allowed to set for 3 min. The sample will then be over turned and the same process repeated. 0.01 mL of inoculum will be spread on the surface of CS. After inoculation, samples will be transferred to whirlpak bags and sealed. CB and BP will be placed in the freezer and sausages in refrigerator. For the high concentration of bacteria, samples will be directly inoculated with stationary phase cells. Lower concentrations of bacteria will be made by serially diluting the stationary phase culture. After 12h under storage conditions, samples will be exposed to UV at high and low intensities for 30,60,90,120,150, and 180s. Midway through each exposure time, the product will be overturned to ascertain that the product gets subjected to UV evenly. After UV exposure, individual sample will be placed aseptically into a whirlpak bag and a 1:9 dilution will be pulsified for 1 min. Serial dilutions using peptone water will be spread-plated on MOX. Colonies will be counted after an incubation period of 35 C for 24 h and reported as log CFU/ g of product.