## 2 Materials and Methods
### Adherence of Bacteria to HeLa Cells  
A total of 4 \(\times\) 10\({}^{5}\) HeLa cells were seeded in 6-well plates and incubated at 37 \({}^{\circ}\)C for 24 h. After PBS washing, HeLa cells were incubated with 1 mL of _Lactobacillus_ suspension at a concentration of 1.5 \(\times\) 10\({}^{9}\) cells/mL at 37 \({}^{\circ}\)C for 1 h, to allow the adhesion of _Lactobacillus_ to cells. Six different _Lactobacillus_ strains were individually used in the experiment including _L. rhamn_s GMNL-74, _L. acidophilus_ GMNL-185, _L. rhamn_s GMNL-680, _L. plantarum_ GMNL-682, _L. rhamn_s GR-1, and _L. reuteri_ RC-14. Then, the cells were washed twice with PBS to remove nonadhering bacteria. For quantitation of the adhering bacteria, the washed cells were lysed in PBS containing 1% triton \(\times\) 100 and centrifuged at 2200 g for 5 min. After removing the supernatant, the pellet was resuspended and serially diluted in PBS and then the appropriate dilution was inoculated onto MRS agar plates, followed by 48-h incubation at 37 \({}^{\circ}\)C. After incubation, the colonies were counted to determine the adhering bacteria number.  
To further examine the ability of _Lactobacillus_ to block the adherence of pathogenic bacteria to cells, 3 different adhesion assays were performed, including exclusion assay, displacement assay, and competition assay [18]. The scheme of the experimental procedure is shown in Figure S1. Three different pathogens were individually used in these adhesion assays including _G. vaginalis_, _S. agalactiae_, and _C. albicans_. In the exclusion assay, the ability of _Lactobacillus_ to interfere with the adherence of vaginal pathogenic bacteria to HeLa cells was examined. 4 \(\times\) 10\({}^{5}\) HeLa cells in 6-well plates were incubated with 1 mL of _Lactobacillus_ suspension (1.5 \(\times\) 10\({}^{9}\)/mL) at 37 \({}^{\circ}\)C for 1 h, to allow the adhesion of _Lactobacillus_to cells. Subsequently, the cells were washed twice with PBS to remove the nonadhering bacteria, and incubated again with 1 mL of bacterial pathogen suspension (1.5 \(\times\) 10\({}^{9}\)/mL) at 37 \({}^{\circ}\)C for 1 h. Finally, the cells were washed, stained with Giemsa stain and examined under the microscope. In displacement assay, the ability of _Lactobacillus_ to displace the already-adhered pathogenic bacteria on HeLa cells was examined. The experiment protocol was the same as the exclusion test, but the incubation sequence was reversed. HeLa cells were first incubated with pathogenic bacterial suspension and then incubated with _Lactobacillus_ suspension. In a competitive assay, HeLa cells were simultaneously incubated with _Lactobacillus_ and pathogenic bacteria suspensions at 37 \({}^{\circ}\)C for 1 h. For microscopy examinations, the cells were fixed with methanol, stained with Giemsa stain and the adherence of pathogenic bacteria was counted under the microscope (BX51, Olympus, Japan). The following formula was used to calculate the inhibition of pathogen adhesion to cells--inhibition rate (%) = [1 \(-\) (mean number of pathogens in _Lactobacillus_ and pathogen co-treatment group/mean number of pathogens in pathogen treatment group)] \(\times\) 100.