To evaluate if the inhibitory effect of Lactobacillus cells could beascribed to the physical interaction with GBS, we screened the ability ofLactobacillus cells to auto-aggregate, as well as the capacity to co-aggregate with Streptococcus cells.As shown in Fig. S1 (Supplementary material), the rate of auto-aggregation of all Lactobacillus tended to increase over time, with a highstrain-specific variability. After 3 h of incubation auto-aggregationpercentages ranged between 0 and 5% (BC8, BC13, BC14) to about30–45% (BC3, BC12).Considering co-aggregation with GBS after 1 h-interaction, wefound that all the Lactobacillus strains that reduced significantly GBSviability by means of cell pellets (L. crispatus BC3 and BC6, L. gasseriBC9, BC13 and BC14, and L. vaginalis BC16) were able to aggregatewith Streptococcus cells (rate of co-aggregation 8–20%; Table S1). Onthe contrary, with the exception of L. crispatus BC8, no significant coaggregation with Streptococcus cells was observed with the remainingstrains (0–3%; Table S1).