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Prevalence and characterization of Listeria spp. in foods and assess its virulence

Vageeshwari, H. A. (2008) Prevalence and characterization of Listeria spp. in foods and assess its virulence. PhD thesis, University of Mysore.

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The broad spectrum of foodborne infections has changed dramatically over the years, as well-established pathogens have been controlled or eliminated and new ones have emerged. The burden of foodborne disease remains substantial. The spectrum of foodborne pathogens includes a variety of enteric bacteria, aerobes and anaerobes, viral pathogens and parasites as well as marine dinoflagellates. Listeria is one of the pathogenic bacteria emerged in 1980’s in the scene of public health causing serious foodborne outbreaks in western countries. This pathogen viewed as emerging one due to its ubiquitous nature, tolerance to adverse conditions and typical characteristics of being able to survive and even multiply in refrigerated food products. In view of the public health significance of Listeria spp., reviews have been documented on varied aspects (Ryser and Marth, 1999). Listeria is widely distributed in nature and can be readily isolated from soil, water, sewage, green plant material, decaying vegetation and numerous species of birds and mammals, including humans (Gray and Killinger, 1966). Listeria monocytogenes is a facultative human pathogen commonly found in the environment and can exist in an intracellular state within monocytes and neutrophils (Schuchat et al. 1992). According to Bergeys Manual of Systematic Bacteriology, Listeria has been placed as a genus in the family Listeriaceae Ph.D. Thesis Synopsis ii under the Order: Bacillales. Listeria are small (1.0-2.0 x 5 μm) Gram positive, facultative anaerobic, rod shaped bacterium. Listeria is a psychrotropic that can survive for long periods in cold storage. It can grow in a wide range of temperatures from –1.50C to 500C and pH of 4.3 to 9.6 (Farber et al. 1989; Hudson et al. 1994). Listeria can be isolated by conventional selective isolation methods (like FDA, USDA and others), which involves steps of enrichment and plating on selective isolation medium. Nucleic acid based methods such as PCR, RT-PCR, multiplex PCR, Nested PCR, RFLP and RAPD as well as immunological methods like ELISA, ELFA and immuno-precipitin have enabled in rapid and specific detection of these organisms, both in pure culture system and in certain foods. Studies relating to incidences of Listeria spp. in foods in India are few, with much emphasis on sea foods (Fuchs and Surendran, 1989; Kamat and Nair, 1994; Jayashekaran et al. 1996; Karunasagar and karunasagar, 2000). Few studies have been carried out to investigate the occurrence of Listeria spp in milk and milk based products (Pednekar et al. 1997; Warke et al. 2000; Barbuddhe et al. 2002), vegetables (Pingulikar 2001) and meat from Indian market (Kamat and Nair, 1994; Barbuddhe, 2002). The reports on neonatal listeriosis (Thomas et al. 1981) and listeriosis during pregnancy (Gupta et al. 2003) and the presence L. Ph.D. Thesis Synopsis iii monocytogenes in clinical samples (Dhanashree et al. 2003) has emphasized the documentation of prevalence of Listeria spp. in the present Indian scenario. In the background of information documented in literature about public health significance of these Listeria species, the present study was done to detect the prevalence of Listeria spp. in different foods. Antibody based and DNA based techniques were developed for rapid detection and the virulence of native isolates were assessed using Drosophila model. The data generated from the above investigations are presented in Ph.D. programme along with introduction, review of literature and summary & conclusion and Bibliography. In this background, it is desired that studies should primarily focus on: • Prevalence of Listeria species including those of L. monocytogenes in foods • Develop detection systems, which can detect large number of Listeria species over that of L. monocytogenes • Assess the virulence factors, which may exist among non-L. monocytogenes cultures The major aspects covered in various sections of review of literature are summarized below.  Foodborne pathogens  Listeria and its species Ph.D. Thesis Synopsis iv  Methods of isolation  Virulence determination  Incidence in food In the third chapter, object and scope of the study has been discussed. The fourth chapter involves four sub-chapters, which focuses on experimental plan, results and discussion. PREVALENCE OF LISTERIA SPECIES IN DIVERSIFIED FOODS Prevalence of Listeria monocytogenes and other Listeria spp. in different foods like milk and milk based products, meat and meat based products, vegetables and vegetable based were assessed, using non-selective cold enrichment technique. The presumptive isolates were further confirmed by morphological, biochemical and cultural characteristics. IMMUNOLOGICAL METHODS FOR THE DETECTION OF LISTERIA MONOCYTOGENES Listeriolysin O was purified by L. monocytogenes cultures and characterized. The pure LLO was used in production of antibody in rabbit and poultry. The produced antibody was used in the detection of L. monocytogenes in pure form and from artificially contaminated milk and market samples. Immunobeads were prepared by coating antibody to protein A beads and immunocapture of L. monocytogenes was carried out from milk. Ph.D. Thesis Synopsis v MOLECULAR METHODS FOR THE DETECTION OF LISTERIA SPP. Primers were designed for the detection of all pathogenic Listeria and different spp. in particular. Uniplex, multiplex, nested and immunoPCR were carried out for the detection of L. monocytogenes in pure cultures and in artificially contaminated milk. The native isolates were confirmed by PCR technique. ASSESSING THE VIRULENCE TRAITS IN LISTERIA SPECIES Native Listeria isolates were assessed for virulence using Drosophila model. The Drosophila was established as a model for pathogenicity assessment in respect of Listeria cultures and other Gram positive and Gram negative bacteria

Item Type: Thesis (PhD)
Uncontrolled Keywords: oodborne infections; Listeria-; Isolation; Selective isolation methods-; FDA; USDA; Fuchs; Milk and milk based products
Subjects: 600 Technology > 01 Medical sciences > 07 Food borne disease
Divisions: Human Resource Development
Depositing User: Food Sci. & Technol. Information Services
Date Deposited: 18 Mar 2010 07:03
Last Modified: 18 Mar 2010 07:03
URI: http://ir.cftri.res.in/id/eprint/9400

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