Vaginal lactobacilli protect against C. albicans and C. trachomatis infections

A normal vaginal microbiota, dominated by lactobacilli, is crucial for the prevention of several urogenital and sexually transmitted infections, including Candida and Chlamydia (Gupta et al., 1998; Spurbeck and Arvidson, 2008; Parolin et al., 2015; Nardini et al., 2016; Foschi et al., 2017; Ñahui Palomino et al., 2017). Some lactobacilli strains, previously isolated from healthy vaginal swabs (Parolin et al., 2015) were tested in order to evaluate their protective role against C. albicans and C. trachomatis infections. Two mechanisms of action at the basis of the protective role of lactobacilli against C. albicans were identified: 1) BC1 and BC9 strains interacting with HeLa plasma membrane caused a modification of polar lipids organization and increased membrane fluidity; 2) BC2, BC11 and BC15 strains acted modulating α5β1 exposure on HeLa plasma membrane. Both mechanisms resulted in the inhibition of C.albicans adhesion to HeLa cells. Furthermore, we aimed to identify vaginal Lactobacilli strains able to interfere with C.trachomatis infection process. Specifically, L. crispatus BC5 was the most active strain in counteract C. trachomatis adhesion to HeLa cells. Importantly, through siRNA silencing of ITGA5 gene, we demonstrated that C. trachomatis needs of α5 integrin subunit for its adhesion and internalization into HeLa cells. Moreover, L. crispatus BC5 was able to protect from C. trachomatis infection by means of a dual mechanism. On the one hand, L. crispatus BC5 interaction with HeLa caused an increase of plasma membrane fluidity and a reduction of α5 integrin exposure on cell surface, making this protein less available for C. trachomatis binding and internalization. On the other hand, L.crispatus BC5 directly interacted with C.trachomatis, grabbing it and preventing its binding to α5 integrin. Interestingly, both in L. crispatus BC5 lysate and BS5 we found a protein similar to α5 integrin which could be responsible for C. trachomatis binding.