Abstract
Lactic acid bacteria (LAB) present many important properties in food manufacturing, such as improvement of physical characteristics and the production of lactic acid that aids in the increase of the shelf life of food products. Also, LAB can suppress growth of pathogens, control of serum cholesterol level, modulate immune system, and improve lactose digestion. Five standard (Lactobacillus paracasei, Lactobacillus helveticus, Lactobacillus fermentum, Bifidobacterium longum and Lactococcus lactis) lactic acid bacterial strains were screened for probiotic potential properties and their ability to antagonize the growth of some enteric pathogens isolated from patients suffering from acute gastroenteritis. The five strains of LAB were resistant to acidic pH and bile salts. Lactobacillus strains showed protein and starch digesting capability on agar plate while B. longum ATCC 15707 and L. lactis subsp. lactis ATCC 11454 showed only protein digestion. In addition, Lactobacillus strains showed antagonistic effects against all pathogenic strains tested. L. paracasei and L. helveticus [culture and cell-free culture supernatant (CFCS)] exhibited the highest antagonistic activity against the tested pathogens followed by L. fermentum. While B. longum and L. lactis subsp. lactis showed weak or no activity against the tested strains. L. paracasei, L. helveticus, and L. fermentum showed potential to be used as probiotic strains with considerable good antagonistic activity against the most important enteric pathogens. Key words: Lactobacillus paracasei, Lactobacillus helveticus, Lactobacillus fermentum, Bifidobacterium longum subsp. longum, Lactococcus lactis subsp. lactis, potential probiotic, antagonistic activity.
Highlights
Foodborne bacterial pathogens, such as Escherichia coli, Salmonella, Shigella, Yersinia enterocolitica and Staphylococcus aureus can cause diseases that ranged from mild diarrhea to severe illness with high mortality (Petri Jr. et al, 2008)
Lactobacillus strains were cultured in De Man, Rogosa and Sharpe (MRS) broth with tween 80 (Biolife Italiana, Milano, Italia) anaerobically at 37°C, B. longum subsp. longum ATCC 15707 were cultured in tryptone soy (TS) broth (Lab M Limited, United Kingdom) anaerobically at 37°C, L. lactis subsp. lactis ATCC 11454 were cultured in Brain heart infusion (BHI) broth (Lab M Limited, United Kingdom) aerobically at 37°C
B. longum subsp. longum and L. lactis subsp. lactis showed only protein digestion, Lactic acid bacteria (LAB) have developed a complex system of proteinases and peptidases which enable them to utilize casein protein found in milk (Smid et al, 1991)
Summary
Foodborne bacterial pathogens, such as Escherichia coli, Salmonella, Shigella, Yersinia enterocolitica and Staphylococcus aureus can cause diseases that ranged from mild diarrhea to severe illness with high mortality (Petri Jr. et al, 2008). Bifidobacterium and Lactobacillus are naturally inhabitants of the human intestinal microbiota, some strains have a satisfactory tolerance to the gastrointestinal transit, good survival in food or pharmaceutical supplements and healthpromoting effects; so, the strategy of probiotic supplementation is the reinforcement of the intestinal microbiota, at least transitory, with health-promoting bacteria to benefit the intestinal balance (Farnworth, 2008). The effects of probiotics depend on the dosage and route of administration (Upadhyay and Moudgal, 2012) Some of these mechanisms are the production of bacteriocins, such as nisin [approved by the US Food and Drug Administration (FDA) since last decade for food preservation and shelf life extension] (Yateem et al, 2008; Collins et al, 2012) or lowering the pH by producing acidic compounds like lactic acid (Psomas et al, 2001). Based on previously reported beneficial properties of probiotics, our study aimed to evaluate the probiotic properties of Lactobacillus paracasei ATCC 25598, Lactobacillus helveticus ATCC 15009, Lactobacillus fermentum EMCC 1346, Bifidobacterium longum subsp. longum ATCC 15707 and Lactococcus lactis subsp. lactis ATCC 11454, including their antagonistic activity against some enteric and food borne-pathogens
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