Lactobacilli extracellular vesicles: potential postbiotics to support the vaginal microbiota homeostasis

Abstract

Background Lactobacillus species dominate the vaginal microflora performing a first-line defense against vaginal infections. Extracellular vesicles (EVs) released by lactobacilli are considered mediators of their beneficial effects affecting cellular communication, homeostasis, microbial balance, and host immune system pathways. Up to now, very little is known about the role played by Lactobacillus EVs in the vaginal microenvironment, and mechanisms of action remain poorly understood. Results Here, we hypothesized that EVs can mediate lactobacilli beneficial effects to the host by modulating the vaginal microbiota colonization. We recovered and characterized EVs produced by two vaginal strains, namely Lactobacillus crispatus BC5 and Lactobacillus gasseri BC12. EVs were isolated by ultracentrifugation and physically characterized by Nanoparticle Tracking Analysis (NTA) and Dynamic Light Scattering (DLS). EVs protein and nucleic acids (DNA and RNA) content was also evaluated. We explored the role of EVs on bacterial adhesion and colonization, using a cervical cell line (HeLa) as an in vitro model. Specifically, we evaluated the effect of EVs on the adhesion of both vaginal beneficial lactobacilli and opportunistic pathogens (i.e., Escherichia coli, Staphylococcus aureus, Streptococcus agalactiae, and Enterococcus faecalis). We demonstrated that EVs from L. crispatus BC5 and L. gasseri BC12 significantly enhanced the cellular adhesion of all tested lactobacilli, reaching the maximum stimulation effect on strains belonging to L. crispatus species (335% and 269% of average adhesion, respectively). At the same time, EVs reduced the adhesion of all tested pathogens, being EVs from L. gasseri BC12 the most efficient. Conclusions Our observations suggest for the first time that EVs released by symbiotic Lactobacillus strains favor healthy vaginal homeostasis by supporting the colonization of beneficial species and preventing pathogens attachment. This study reinforces the concept of EVs as valid postbiotics and opens the perspective of developing postbiotics from vaginal strains to maintain microbiota homeostasis and promote women’s health.

Use of probiotic lactobacilli in the treatment of vaginal infections: In vitro and in vivo investigations

“…The potential benefits of probiotic lactobacilli have been Investigated in vitro with AV pathogens. Extracellular vesicles, phenyl-lactic acid, bacteriocins, and exopolysaccharides, isolated from lactobacilli display remarkable antioxidant and antiproliferative activity and inhibit S. aureus, E. faecalis, S. agalactiae , and E. coli with noticeable antibiofilm activity ( Xiu et al., 2020 ; Abdul-Rahim et al., 2021 ; Croatti et al., 2022 ; Jiang et al., 2022 ). Studies have shown that lactobacilli can inhibit S. aureus through interfering with the staphylococcal quorum-sensing system agr , a key regulator of virulence genes, and by suppressing the generation of toxic shock syndrome toxin-1 in S. aureus ( Li et al., 2011 ; Singh et al., 2022 ).…”

Microorganism-derived extracellular vesicles: emerging contributors to female reproductive health

“…EVs have been found to promote the colonization of Lactobacillus spp., while reducing the adhesion of pathogenic species. 69 69 Beyond bacterial adhesion, some evidence suggests that EVs may contribute to high recurrence rates of BV by facilitating the formation of biofilms in the vagina (Fig. 4).…”

“…72 Further work could be done to determine which specific cargoes may play a role in these observations. 69 A Lactobacillus spp.-dominated vaginal microbiome is associated with a decreased risk of sexually transmitted infections, including HIV-1. These protective properties are facilitated through several biological mechanisms: maintenance of the mucosal barrier, inactivation of HIV-1 via acidification of the vagina, and induction of host immune response against HIV-1.…”

“…EVs have been found to promote the colonization of Lactobacillus spp., while reducing the adhesion of pathogenic species. 69 By pretreating cervical cells with L. crispatus - and L. gasseri -derived EVs, Croatti, et al demonstrated increased adhesion of lactobacilli in vitro , accompanied by reduced adhesion of Escherichia coli , Staphylococcus aureus , Streptococcus agalactiae , and Enterococcus faecalis . 69 Beyond bacterial adhesion, some evidence suggests that EVs may contribute to high recurrence rates of BV by facilitating the formation of biofilms in the vagina (Fig.…”

“…72 Further work could be done to determine which specific cargoes may play a role in these observations. 69…”