Isolation of anti-listerial bacteriocin producing Lactococcus lactis CFR-B3 from Beans (Phaseolus vulgaris)

摘要

Contamination of food samples by Listeria monocytogenes is a major cause of food-borne infections. Controlling the growth of Listeria sp. by application of bacteriocin or bacteriocin producing-organism in foods is one of the challenges in the development of effective bio-preservation process. The objective of this study was to isolate and to characterize bacteriocinogenic strain Lactococcus lactis CFR-B3 from Indian beans. Bacterial strain of Pediococcus acidilactici NRRL B1153 was used as indicator to screen bacteriocin production. The culture was found to produce class IIa heat-stable anti-listerial bacteriocin of MW ~ 5 kDa. The use of food-grade organism as an indicator for screening bacteriocinogenic strains of lactic acid bacteria circumvent the need for using pathogenic cultures such as listeria spp. The native isolate Lc. lactis CFR-B3 finds its application in the preservation of vegetables due to its prevalence in the same ecological niche. Source of fund: This work was financially supported from the institute project under MLP-0304 Introduction Consumption of raw and fresh vegetables is known to be an essential aspect of all healthy food habits. Several culinary vegetables being consumed are known to be nutritious in the human diet. However, the possible spread of pathogenic bacteria in these foods has not viewed seriously. Listeriosis, caused by List monocytogenes, is a major food borne infection in humans. In the United State, as per the report by the Centre for Disease control, an estimated 2, 500 persons become seriously ill with listeriosis every year. Of them atleast 20% cases lead to fatality. One of potential source of pathogenic outbreak is contaminated food, fresh vegetables etc. Several reports indicated that different serotypes of List. monocytogenes transmit via dairy products (Cheese), meat samples and raw vegetables. As Listeria sp have the ability to grow at low temperature, cold storage of vegetables act as selective advantage for this species (Farber and Peterkin, 1991, Cotter et al., 2005; Resenquist et al., 2005). Incorporation of bacteriocin or bacteriocin producing lactic acid bacteria (LAB) in food has advantage in preservation by inhibiting the growth of food- borne pathogens like List. monocytogenes (Drider et al., 2006). A recent survey conducted jointly by the UK Health Protection Agency and local authority body LACORS uncovered two products with listeria levels above the EU's regulatory limit. About 5 per cent of mixed raw vegetable salads in the UK were found to be contaminated with Listeria monocytogenes (Little et al., 2007). Indian beans, apart from its sole use in Indian curry, is being used for the preparation of several culinary dishes that are being served during normal meals. These include salad, vegetable soup, vegetable sandwitch, vegetable rolls, etc. Beside normal practices of minimal processing of the beans by MAP, the pathogenic bacteria can multiply during storage and transport. In order to ensure safety during raw consumption and to minimize the spread of pathogenic bacteria, biopreservation practices can be adopted that include the use of bacteriocinogenic cultures of LAB isolated from the same ecological niche as protective cultures (Kelly et al., 1998; Cotter et al., 2005; Pounce et al., 2007). Among LAB, Lactococcus lactis represent one of the important species, widely known for the production of nisin. Nisin is a ribosomally synthesized antimicrobial peptide, approved by FDA to be used for the preservation of canned foods and dairy products (Delves-Broughton et al., 1996). However, several reports indicated that this bacterium also produces other novel, class IIa, non-lanthionine group of bacteriocin (Lee et al., 1999; Ghrairi et al., 2005). The objective of this study was to characterize the bacteriocin producing culture of Lactococcus lactis isolated from beans using classical and molecular biology techniques and partial characterization of bacteriocin. Material and