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Highly publicized outbreaks of food-borne illness since 1993, primarily caused by bacteria such as E. coli O157:H7, Salmonella spp. and Listeria monocytogenes, elicited intense consumer concern about meat safety. Listeriosis affects approximately 2,500 people per year resulting in approximately 500 deaths. Symptoms of this disease include fever, muscle aches, diarrhea and nausea. More serious symptoms may include headaches, stiff neck, confusion, dizziness or convulsions. Listeriosis is caused by Listeria monocytognes (L. monocytogenes), a bacterium that may be present in pre-packaged luncheon meats, soft cheeses such as brie and camembert, as well as in raw meat such as chicken, pork or beef. This bacterium has the ability to continue to grow at temperatures normally associated with average refrigeration levels. However, the risk of contracting Listeriosis can be dramatically reduced by cooking leftovers or ready to eat foods thoroughly.
The USDA, FDA, CDC, Health and Human Services (HHS) and other governmental agencies are working hard to reduce the incidence of listeriosis and other foodborne illnesses. HHS has set national health objectives for listeriosis that aim to lower the incidence to 0.25 cases per 100,000 by the year 2010. Other efforts include Hazard Analysis Critical Control Point (HACCP) requirements for meat, poultry and seafood. To monitor and assess the effectiveness of these efforts better detection and identification tools for pathogens are needed.
Accurate and rapid pathogen testing methods are highly sought after by the food industry. Detection of L. monocytogenes is no exception to this need because the government has established a zero tolerance standard. Typical detection methods require enrichment, isolation and biochemical testing before a positive identification can be made. Commercially available rapid detection kits save time but detect all species of Listeria not just L. monocytogenes. Current antibodies used in these kits and in other immunological assays use antibodies specific for Listeria species. The lack of specificity is often due to cross-reaction of antibodies used in these methods. The cross reaction of these antibodies to surface proteins on other nonpathogenic Listeria and non-Listeria bacteria can cause false positive reactions costing the companies money and time. The ideal antibody should be specific and maintain a strong reaction with all L. monocytogenes strains. The objectives of this research are to develop antibodies specific for L. monocytogenes by targeting unique surface proteins.
Methodology and Findings
This research compared the L. monocytogenes genome to L. innocua (a non-pathogenic species of Listeria) and identified nine surface proteins specific to L. monocytogenes. Segments of these nine proteins were used to develop antibodies in rabbits. All nine antibodies were screened against a panel of L. monocytogenes, nonpathogenic Listeria, and non-Listeria bacteria. Two of the nine antibodies showed a specific reaction to L. monocytogenes. These two antibodies will be characterized further and used in the development of rapid detection methods.
The CDC (Centers for Disease Control) considers the food-borne pathogens (i.e. E. coli O157:H7, Salmonella spp., and Listeria monocytogenes) to be a significant public health risk. The food industry is under constant battle to detect and eliminate these pathogens from the food supply. The results of this study suggest that there are specific antibodies that could be used to develop a rapid detection method for Listeria monocytogenes in order to ensure a safe food supply, protect public health and save companies time and money.