Will a high adhering capacity in a probiotic strain guarantee exclusion of pathogens from intestinal epithelia

Probiotics are described as microorganisms that exert both beneficial and therapeutical effects when administered to an animal or human host. High adhesion to gut epithelium was proposed to be crucial for the selection of optimal probiotic strains. Two highly adherent bifidobacterial strains of human origin (Bifidobacterium bifidum CIDCA 537 and Bifidobacterium bifidum CIDCA 5310) were tested for their abilities to inhibit cell attachment and cell invasion of a diarrhoeagenic Salmonella arizonae isolated from-a clinical sample. Both strains which had adhered to Caco-2 monolayers before the addition of Salmonella arizonae could not prevent adhesion of this pathogen. Moreover, if Bifidobacterium bifidum CIDCA 537 had been previously frozen the adhesion of Salmonella arizonae to enterocyte-like cells was enhanced. Go-aggregation experiments indicated that this increment in pathogens attachment was presumably due to the formation of mixed aggregates with bifidobacterial strains. Bifidobacterium bifidum CIDCA 5310 seemed to be effective in reducing Caco-2 cells invasion of Salmonella arizonae, whereas strain CIDCA 537 did not. The data suggest that although adhesion to epithelial surfaces is considered an important prerequisite for probiotic activity, high adhesiveness may not guarantee protective properties in a selected strain. We highlight here the strain-dependent character of the 'probiotic effect' and the importance of in vivo experiments for the preparation of dietary adjuncts. (C) 1999 Academic Press.