The aim of the present study was firstly to isolate probiotic cultures that either protect against gastrointestinal colonization and infection by foodborne pathogens. Secondly, to investigate if isolated strains are suitable for application in dairy products. Lactobacillus strains of dairy product and gastrointestinal (GI) origin were tested for their ability to inhibit Listeria monocytogenes and Salmonella typhimurium in vitro. Strains that inhibited growth of Listeria and Salmonella, in an agar overlay assay, were selected for further studies. In these further studies, the protection against the pathogen was assessed in animal models. This assessment involved treating mice (BALB/c) with selected Lactobacillus cultures, after challenge with Listeria or Salmonella. Symptoms of disease were indicated by a loss of animal body weight. GI colonization was assessed by monitoring faecal levels of the pathogen.
The protective effect of cultures was monitored by recording animal body weight, and faecal levels of pathogen. One day after challenge with Listeria monococytogenes, faecal levels of Listeria reached 10 6 cfu/g in most animals. In contrast, animals given L. acidophilus LAFTI® L10 (L10) in conjunction with L. monocytogenes displayed significantly lower (p < 0.01) levels of faecal Listeria. Using a similar model, animals challenged with a single dose of Salmonella lost approximately 14% of their pre-experimental body weight. In contrast, animals given L. paracasei LAFTI® L26 (L26) displayed no signs of infection or loss of body weight. It was concluded that L26 protects against Salmonella infection, and that L10 reduces the ability of Listeria monocytogenes to survive in the mouse GI tract, which may reduce the pathogens ability to invade and infect the animal.
Subsequently, yoghurt was prepared by inoculating a standard yoghurt base with L10, L26 and B. lactis LAFTI® B94 (B94) and yoghurt cultures. Post-acidification and survival of these probiotic cultures was monitored during storage of the yoghurt. Fermentation was terminated at pH 4.5, immediately cooled to 4°C, and stored for 6 weeks. Populations of L10, L26, B94 and pH were monitored weekly. No or minimal viability losses of LAFTI® cultures occurred during the storage of yoghurt. Similarly, there was no or minimal post acidification during storage of yoghurt fermented by these novel probiotic strains. Results presented indicate that L10 and L26 may be used for production of functional probiotic dairy products with desirable technological properties. These cultures may contribute to increased protection against infection, and safety of products that occasionally contain potentially pathogenic bacteria.
Back to the Publications & Presentations 2002 overview
