2.4. Co-Aggregation Assay

A co-aggregation assay was adapted from Pessoa et al. [25]. For the co-aggregation assay, the Lactobacillus sp. suspension was prepared similarly to the auto-aggregation assay. The G. vaginalis suspension was prepared and standardized to 1 × 10⁸ CFU/mL in 0.01 M PBS. Each Lactobacillus sp. suspension (1 mL) was mixed with the same volume of G. vaginalis suspension, and the mixture was vortexed for 10 s prior to gravity sedimentation. Control tubes contained 2 mL of each bacterial suspension alone. The absorbance of the suspensions was read at 600 nm in a spectrophotometer after a 3-h incubation at 37 °C. Co-aggregation was calculated using the following formula: co-aggregation (%) = [(Ax+Ay)/2−A (x+y)] / [(Ax+ Ay)/2] %, where Ax and Ay indicate the absorbance of strains in the control tubes, and A (x + y) indicates the absorbance of the mixtures.