African Journal of Microbiology Research Vol. 1 (6), 065-078, November, 2007          
ISSN 1996-0808 © 2007 Academic Journals

The presented study aims to characterize Lactobacillus acidophilus DSM 20079 and DSM 20242 and Bifidobacterium bifidum DSM 20082, DSM 20215, DSM 20239 and DSM 20456 strains. Within the framework of the performed investigations, the author evaluated their biochemical properties, resistance to antibiotics, antagonism towards selected pathogens as well as the effect on their survivability of different environmental conditions with special emphasis on the conditions prevailing in the human gastrointestinal tract. The performed experiments revealed significant differences between the examined bacterial species as well as between strains of the same species. All the examined strains were characterized by diverse biochemical properties, resistance to antibiotics and showed antagonistic action against Helicobacter pylori bacteria. The tested strains of the L. acidophilus bacteria were found to exhibit antagonistic activity against Escherichia coli and Salmonella enteritidis bacteria, although the observed activity was smaller in comparison with the antagonistic activity against H. pylori. These data confirm reports about the antagonistic effect of probiotic bacteria on the growth of pathogenic bacteria. All the examined bacterial strains fulfil the basic criterion expected from probiotic strains, that is, are capable of surviving in the ‘in vitro’ conditions of the gastrointestinal tract, at low pH and in the presence of bile salts.

Key words: Bifidobacterium bifidum, Lactobacillus acidophilus, probiotic, antibiotic resistance, acidity resistance, bile tolerance, antagonistic activity.