Bile stimulates cell surface hydrophobicity, Congo red binding and biofilm formation of Lactobacillus strains

Seventeen Lactobacillus strains were tested for cell surface hydrophobicity (CSH) using the salt aggregation test (SAT) and Congo red binding (CRB) assay. CRB was dependent on pH and ionic strength and was protease-sensitive. In the presence of 100 μg mL(-1) cholesterol, the CRB was significantly reduced. Autoaggregating (AA) Lactobacillus crispatus strains showed 50% more CRB than the reference strain, the curli-producing Escherichia coli MC4 100. CRB of L. crispatus 12005, L. paracasei F8, L. plantarum F44 and L. paracasei F19 were enhanced when grown in Man Rogosa Sharpe (MRS) broth with 0.5% taurocholic acid (TA) or 5% porcine bile (PB) (P < 0.05). CSH was also enhanced for the non-AA strains L. plantarum F44, L. paracasei F19 and L. rhamnosus GG when grown in MRS broth with 0.5% TA, 5% PB or 0.25% mucin, with enhanced biofilm formation in MRS broth with bile (P < 0.05). Two AA strains, L. crispatus 12005 and L. paracasei F8, developed biofilm independent of bile or mucin. In summary, under bile-stressed growth conditions, early (24-h cultures) biofilm formation is associated with an increase in hydrophobic cell surface proteins and high CRB. Late mature (72-h culture) biofilm contained more carbohydrates, as shown by crystal violet staining.