Characterization of intestinal lactobacilli as putative probiotic candidates

Aims: To use antioxidative activity and antagonistic properties of lactobacilli against selected pathogens and members of the normal microflora as a basis for screening probiotic candidates. Methods and Results: Antagonistic activity of lactobacilli against target bacteria in both microaerobic and anaerobic environments was tested. Production of antagonistic metabolites (ethanol, hydrogen peroxide (H₂O₂), acetic, lactic and succinic acid) by lactobacilli as well as their total antioxidative activity were assessed. In general, the lactobacilli tested were most effective against Gram-negative bacteria and their antagonistic activity was strain-specific. However, obligately heterofermentative lactobacilli had the strongest activity when tested in a microaerobic environment. Additionally, facultatively heterofermentative lactobacilli were equally effective in either milieu and produced significant levels of acetic and lactic acid. Moreover, obligately homofermentative lactobacilli had high H₂O₂ production and total antioxidative activity but weak antagonistic activity. Conclusions: Antioxidative and antagonistic activity of intestinal lactobacilli is strain-specific but typically can be related to their fermentation type which may be used for rapidly screening large numbers of lactobacilli for probiotic candidates. Significance and Impact of the Study: This study represents the first report on the utilization of group characteristics to screen lactobacilli intended for specific probiotic use. Such uses include the targeting of particular gut niches and pathogens as well as allowing for long-term benefits to the host.