Probiotic features of Lactobacillus strains isolated from Ragusano and Pecorino Siciliano cheeses

Abstract

In the present study 177 Lactobacillus spp. strains, isolated from Ragusano and Pecorino Siciliano cheeses, were in vitro screened for probiotic traits, and their characteristics were compared to those of Lactobacillus rhamnosus GG, commercial strain. Based on acidic and bile salt resistance, thirteen Lactobacillus strains were selected. The multiplex-PCR application revealed that nine strains belonged to L. rhamnosus species and four to Lactobacillus paracasei species. All selected strains were further investigated for transit tolerance in simulated upper gastrointestinal tract (GI), for adhesion capacity to human intestinal cell lines, for hydrophobicity, for co-aggregation and auto-aggregation and for antimicrobial activities. Moreover, antibiotic resistance, hemolytic and bile salt hydrolase activities were investigated for safety assessment. Viable counts after simulated gastric and duodenal transit revealed that overall the selected lactobacilli tolerated better pancreatic juice and bile salts than acidic juice. In particular, three L. rhamnosus strains (FS10, FS2, and PS11) and one L. paracasei strain (PM8) increased their cell density after the simulated GI transit. The same strains showed also high percentage of auto-aggregation and co-aggregation with Escherichia coli. All strains were effective against both Staphylococcus aureus and E. coli and variability was achieved versus Listeria monocytogenes and Enterococcus faecalis used as pathogenic indicator strains. Different behavior was revealed by strains for adhesion ability and hydrophobicity, which are not always linked each other and are strongly strain-dependent. From the safety point of view, no isolate showed hemolytic and bile salt hydrolase activities, except one, and most of the strains were sensitive to a broad range of clinical antibiotics. This work showed that the L. rhamnosus FS10 and the L. paracasei PM8 are good promising probiotic candidates for further in vivo investigations.

Keywords: Acidic and bile resistances; Antibiotic resistance; Principal component analysis; Probiotics; Safety assessment; Simulated GI transit tolerance.