Initial adhesion assays were realized through different experimental settings, simulating dysbiosis conditions (ES1 and ES4), candidiasis (ES2), and healthy vaginal microbiota (ES3). The lactobacilli displacement was firstly evaluated on low levels (ES1 and ES2) against low and high concentrations of C. albicans and then on high levels (ES3 and ES4), as shown in Additional file 5. On low levels of lactobacilli, the range of displacement was between 15 and 99% (see Fig. 1). At ES1, C. albicans ATCC10231 induced bigger displacement of L. gasseri IMAUFB014 (84%; P = 0.010, two-way ANOVA) and H59.2 (83%; P < 0.001, two‐way ANOVA) showing significant differences among C. albicans isolates (Tukey's post hoc, P < 0.05). Likewise, all C. albicans isolates showed to be statistically different in their displacement ability among the L. gasseri. C. albicans from healthy vaginal microbiota was able to displace 99% of L. gasseri IMAUFB014, while C. albicans isolated from candidiasis demonstrated 99% of displacement against L. gasseri JCM1131. At ES2, no statistically significant differences were found in the displacement among L. gasseri. At ES3, C. albicans isolated from candidiasis showed statistical differences, evidencing a greater ability to displace L. gasseri H59.2 (90%; P < 0.001, two‐way ANOVA). L. gasseri JCM1131 showed only 15% of displacement by C. albicans isolated from candidiasis, being statistically different when compared to C. albicans ATCC10231 (83%; P = 0.001, Tukey's post hoc) and C. albicans isolated from healthy vaginal microbiota (84%; P < 0.001, Tukey's post hoc). At ES4, L. gasseri JCM1131 showed 65% of displacement by C. albicans isolated from candidiasis, but it only evidenced a statistically significant difference against C. albicans isolated from healthy vaginal microbiota (93%; P = 0.045, Tukey's post hoc).
The adhesion inhibition of C. albicans by L. gasseri was also evaluated (see Fig. 2). At ES1, L. gasseri JCM1131 and L. gasseri IMAUFB014 showed statistically significant differences among C. albicans isolates (L. gasseri JCM1131 P = 0.006, and L. gasseri IMAUFB014 P = 0.002; two-way ANOVA). L. gasseri JCM1131 evidenced the lowest inhibition rate against C. albicans ATCC10231 (27%), illustrating statistically significant values when compared against C. albicans isolated from candidiasis (60%; P = 0.016, Tukey's post hoc) and C. albicans isolated from healthy vaginal microbiota (67%; P = 0.006, Tukey's post hoc). While L. gasseri IMAUFB014 showed a more efficient inhibition rate against C. albicans isolated from candidiasis (76%; P = 0.002, Tukey's post hoc). At ES2, L. gasseri H59.2 was the only strain to show statistically inhibition values among C. albicans isolates (P = 0.008; two‐way ANOVA). Again at ES3, only L. gasseri H59.2 demonstrated a statistically significant difference in its inhibition ability (P = 0.030; two‐way ANOVA) against C. albicans ATCC10231 (61%) and C. albicans isolated from candidiasis (89%; P = 0.034, Tukey's post hoc). At ES4, all C. albicans isolates showed statistically significant inhibition rates (C. albicans ATCC10231: P = 0.010; C. albicans isolated from candidiasis: P = 0.011; C. albicans isolated from healthy microbiota: P = 0.025, two‐way ANOVA analysis). L. gasseri IMAUFB014 showed the highest inhibition rate against C. albicans isolated from healthy microbiota (80%), being statistically different to C. albicans ATCC10231 (47%; P = 0.016, Tukey's post hoc).
Probiotic ability of Lactobacillus plantarum ATCC14917 was realized against C. albicans ATCC10231 and compared with L. gasseri evidencing significant displacement values and inhibition values (see Additional file 6 and Fig. 3A). The displacement values of L. plantarum were 23% and 54% against low (ES1) and high (ES2) levels of C. albicans, respectively. These values were significantly inferior to L. gasseri (ES1: 61–99% and ES2: 82–96%), more exactly: L. gasseri IMAUFB014 (ES1: P < 0.001and ES2: P = 0.002, Tukey's post hoc); L. gasseri JCM1131 (ES1: P = 0.003 and ES2: P = 0.025, Tukey's post hoc); and L. gasseri H59.2 (ES1: P < 0.001 and ES2: P = 0.012, Tukey's post hoc). At ES3, L. plantarum was only displaced by 31% evidencing again a better resistance when compared to L. gasseri (ES3: 83–95%), specifically: L. gasseri IMAUFB014 (P < 0.001, Tukey's post hoc); L. gasseri H59.2 (P < 0.001, Tukey's post hoc); and L. gasseri JCM1131 (P = 0.001, Tukey's post hoc). At ES4, L. plantarum was displaced 94% without statistical differences. As shown in Fig. 3B, the adhesion inhibition of C. albicans by L. plantarum demonstrated a superior activity in ES1 (81%) and ES2 (58%) when compared to L. gasseri (ES1:27–73% and ES2:1–49%; both P < 0.001, two-way ANOVA). At ES3 and ES4, L. plantarum showed the lowest inhibition rate (50–56%), but no statistically significant differences were found.