ANTIMICROBIAL ACTIVITY AND SURVIVAL IN THE GASTROINTESTINAL TRACT AND FOOD PROCESSING CONDITIONS OF LAB AND BIFIDOBACTERIA STRAINS.

Lactic acid bacteria and bifidobacteria are natural inhabitants of the human intestinal tract with health–promoting effects. In this work, the antimicrobial activity of 92 LAB and bifidobacteria strains (Lactobacillus spp., Bifidobacterium spp., Pediococcus spp., Leuconostoc spp) was tested in vitro against 3 strains of Campylobacter jejuni. The results evidenced that 9 LAB and 2 bifidobacteria strains possessed antimicrobial activity against all C. jejuni strains, which was not caused by acid formation. The nature of the compounds responsible for this activity has been studied by treatment with different enzymes, thus evidencing a possible proteinaceus nature of them. The eleven strains have been characterized for their antibiotic resistance profile and assayed for their survival in the GI tract (viability at pH 2.5 and resistance to bile salts). Furthermore, their ability to survive under two different food processing conditions (heat and osmotic stress) was evaluated. The results showed that most of the strains rapidly loose their viability at low pH, whereas treatment with bile salts did not affect the survival of the majority of them. Almost all strains survived well at both processing conditions tested. Tests are being performed to evaluate the colonization of the selected strains in poultry and their in vivo activity against C. jejuni.