Characterization of bacterocin-like substances produced by two local Lactobacillus paracasei subsp. paracasei strains

Abstract

The increasing consumer awareness of the risks derived not only from food borne pathogens, but also from the artificial chemical preservatives used to control them, has led to an increased interest in food -grade preservatives of biological origin. In this respect, special interest has been focused on the antimicrobial bacteriocins and the lactic acid bacteria producing them which are considered safe biopreservatives. In the present study, sixty nine lactobacillus strains isolated from retail samples of local foods and dairy products were screened for bacteriocin production Of the 47 Lactobacillus isolates found to be bacteriocin-like substances producers, five best strains which showed the strongest antibacterial activity against E.coli; Listeria monocytogenes; Bacillus cereus; Salmonella enteritides; and Staphylococcus aureus, were selected and identified, among these isolates, two were found belong to Lb. paracasei subsp. paracasei. The bacteriocin-like substances (BLS) produced by these strains were tested for characteristics that could determine their usefulness as food biopreservatives. The two BLS retained most of their bacterial activity even after autoclaving and after extended refrigerated and freezing storage, as well as after exposure to organic solvents or surfactants, and they remained functional over a wide pH rang of 3.0 to 12.0 and tolerated up to 20.0% sodium chloride. In addition they exhibited broad antimicrobial spectra against not only G + bacteria but also against Gbacteria and yeasts. These results suggest that BLS produced by two local Lactobacillus strains has an application potential as food biopreservatives, and may be used as alternatives or complimentary for antibiotics. Keywords: Bacteriocins, Lactobacillus paracasei subsp. paracasei, antibiotics. INTRODUCTIONQuality and safety of foods have always a significant public health concern. Although various methods are employed for the preservation of foods, an increasingly health conscious public may seek to avoid foods that have undergone extensive processing or which contain artificial chemical preservatives. This provided an increased interest in food-grade preservatives of biological origin. In this respect, special interest has been focused on bacteriocins produced by bacteria.Bacteriocins are defined as ribosomally synthesized peptides or proteins with antagonistic activity against species genetically closely related (De Vuyst and leroy, 1994), and some of them are inhibitory towards food spoilage and food borne pathogenic bacteria (Zamfir et al., 1999). The aim of using bacteriocins to improve quality and safety of foods has stimulated intensive research efforts in recent years (Deegan , 2006). Although bacteriocins are produced by many Gram-positive and Gramnegative bacteria, those produced by lactic acid bacteria (LAB) are of particular Gamal-Eldin,H. et al.