In-vitro characterization of potentially probiotic Lactobacillus strains isolated from human microbiota: interaction with pathogenic bacteria and the enteric cell line HT29

Among the various tests commonly used for selecting probiotic microorganisms, the tolerance to gastrointestinal transit conditions remains being commonly used to evaluate the probiotic potential of the strains. Besides, the adhesion to epithelial cells and the competition with pathogens constitute significant traits for evaluating the colonization ability and functional performance of candidate strains. In this study, a total of 13 lactic acid bacteria strains isolated from human feces were first identified by biochemical tests and 16S rRNA gene sequencing, and then characterized in vitro for their tolerance to gastrointestinal conditions, hemolytic activity, and antibiotics sensibility. The isolates were identified as Lactobacillus fermentum (06), Lactobacillus rhamnosus (04), Lactobacillus plantarum (02), and Lactobacillus salivarius (01). The adhesion to epithelial cells HT29 was shown to be a strain-dependent character. L. fermentum 88 and L. plantarum 9, being the ones showing higher adhesion values. They were further characterized by determining their antimicrobial activity, hydrophobicity, co-aggregation, antioxidant activity, as well as the ability to inhibit the adhesion of pathogens to the human epithelial cell line HT29. Moreover, these two strains were able to reduce the adhesion of Escherichia coli to HT29 cells, although they failed for inhibiting the adhesion of other pathogens such as Cronobacter sakazaki or Salmonella enterica. These results point out the importance of considering the ecological fitness of the strains in selecting probiotic bacteria and the potential of some of the analyzed strains for the development of food products.