All bacterial strains used in this study are listed in Table 1. All Neisseria strains and Streptococcus pyogenes strains were grown on GC agar (Acumedia) containing Kellogg's supplement (Kellogg et al., 1963). Pseudomonas aeruginosa, Staphylococcus aureus, all Salmonella strains and the E. coli strains were grown on Luria agar (Acumedia). The Lactobacillus strains were grown on Rogosa agar (Oxoid). All aforementioned bacteria were cultured at 37°C and 5% CO2 for 16–18 h before experimentation. The Helicobacter pylori strains were grown on Colombia blood agar (Acumedia) supplemented with 5% defibrinated horse blood and 5% inactivated horse serum (Håtunalab) for 3 days at 37°C under microaerophilic conditions (5% O2, 10% CO2). Before each experiment, the bacteria were washed once and resuspended in cell culture medium without serum that was specific to the cell line that was used.