Studies on Antimicrobial Activity and Characteristics of Bacteriocins Produced by Lactobacillus strains Isolated from Milk of Domestic Animals

摘要

Lactobacilli strains were isolated from the milk of domestic animals for potential probiotic. A total of 120 milk samples (40 each from buffalo, cow and goat) were analyzed and 110 Lactic Acid Bacteria (LAB) were identified, out of these 43 were identified as probiotics, (L. acidophilus, L. bulgaricus, L. plantarum, L. lactis and L. rhamnosus). Out of these, 11 isolates were potential probiotics, which includes L. plantarum (C1, C4, C7, G7, G8 and B14) and L. rhamnosus (B13, C5, G4, G10 and G18). Their bacteriocins showed a broad inhibitory spectrum against the indicator organisms tested. The bacteriocins produced by L. plantarum (C4, G7) and L. rhamnosus (G18) showed prominent antimicrobial activity, resistance to heat at 1210C and tolerate acidic pH 3 but sensitive to pH 9 indication strong probiotic potential. These isolated LABS, exhibiting excellent probiotic characteristics, can be use in the protection and improvement of intestinal microbial flora and contribute health benefits to consumers. Introduction Lactic acid bacteria (LAB) widely distributed in the nature and occurring indigenous microflora in raw milk that play an important role in many food and feed fermentations with increased shelf life. Within the LAB group, the genus Lactobacillus is the most widely encountered for probiotics because they display numerous antimicrobial activities. This is mainly due to the production of antimicrobial metabolites including organic acids, hydrogen peroxide and bacteriocins. Among these, bacteriocins have gained increasing interest. Bacteriocins, as defined by Ogunbanwo et al, (2003) are proteinaceous compounds produced by bacteria that exhibit a bactericidal mode of action against related as well as unrelated organisms. Bacteriocin generally exert their antimicrobial action by interfering with the cell wall or the membrane of target organisms, either by inhibiting cell wall biosynthesis or causing pore formation, subsequently resulting in death (Sullivan et al, 2002). The bacteriocin from food grade LAB appear to qualify as ideal food biopreservative primarily because they have proven non-toxic to humans, do not alter the nutritional properties, effective at low concentration, active under refrigerated storage and can be used even in the preservation of foods by the use of bacteriocin produced by LAB. Bacteriocins produced by LAB have been the focus of many investigations because of their particular importance in the dairy industry. Several bacteriocins with industrial potential have been purified and characterized. The highly promising results of these studies underline the important role that functional, bacteriocinogenic LAB strains may play in the food industry as starter cultures, co-cultures, or bioprotective cultures, to improve food quality and safety (De vuyst and Leroy, 2007). Many LAB produce proteinaceous antimicrobial bacteriocins, some of which could provide valuable alternatives to traditional therapeutic antibiotics for the treatment of infectious diseases (Ryan et al, 1989). Bacteriocins are inhibitory towards sensitive strains and are produced by both Gram positive and Gram negative bacteria (Kacem et al, 2005). Bacteriocins have attracted a great interest in food industry due to their application potentiality in food preservation. It is relatively hydrophobic and heat stable (Klaenhammer, 1993). The purpose of this work was to isolate potential probiotic Lactobacillus strains and determined the characterization and antimicrobial activity of bacteriocins. Materials and Methods Isolation and identification of Lactobacillus species: A total of 120 milk samples (40 each from cow, goat and buffalo) were randomly collected in sterilized glass bottles. Milk was serially diluted to 10-5_10-6 using sterile distilled water and 0.1mL plated on to sterile de-Mann, Rogosa and Sharpe (MRS) agar. The MRS plates were maintained in microaerophilic condition and incubated at 37°C for 48h. After incubation well-isolated typi