Antimicrobial Compounds Produced by Vaginal Lactobacillus crispatus Are Able to Strongly Inhibit Candida albicans Growth, Hyphal Formation and Regulate Virulence-related Gene Expressions

Abstract

The female vaginal environment contains diverse microorganisms, and their interactions play significant roles in health and disease. Lactobacillus species are the predominant vaginal microorganisms in healthy women and relevant as a barrier to defense against pathogens, including Candida albicans. The yeast-to-hyphae transition is believed to be a determinant of C. albicans pathogenesis. In this study, we investigated the effects of vaginal isolates of L. crispatus (seven strains), L. gasseri (six strains), and L. jensenii (five strains) on growth, hyphal formation and virulence-related genes expression of C. albicans ATCC 10231. We found that the L. crispatus showed the most significant antimicrobial activities in microplate-based liquid medium assay (P < 0.05). All seven cell-free supernatants (CFS) from L. crispatus strains reduced the growth of C. albicans by >60%. The effects might be due to their productions of some secretory antimicrobial compounds in addition to H2O2 and organic acids. Furthermore, each of the CFS of Lactobacillus strains was found to significantly suppress the yeast-to-hyphae transition of C. albicans under hyphae-inducing conditions (RPMI 1640 medium supplemented with 10% fetal bovine serum). The hyphae inhibition rates of C. albicans treated by CFS from L. crispatus, L. gasseri, and L. jensenii were 88.3 ± 3.02%, 84.9 ± 6.0%, and 81.9 ± 6.2%, respectively. Moreover, the expression of hyphae-specific genes (ALS3, HWP1, ECE1, EAP1, and SAP5) and transcriptional regulatory genes (EFG1, TEC1, and NRG1) were analyzed using quantitative real-time PCR. The results demonstrated that L. crispatus CFS significantly down-regulated the expression of hyphae-specific genes ALS3 (0.140-fold)), HWP1 (0.075-fold), and ECE1 (0.045-fold), while up-regulated the expression of the negative transcriptional regulator gene NRG1 with 1.911-fold. The antimicrobial compounds from L. crispatus B145 against Candida growth were heat stable and protease resistance, but those against hyphal formation were partially sensitive to the same treatments. Our novel findings suggest that L. crispatus, a dominant Lactobacillus species associated with a healthy vagina, could strongly inhibit C. albicans growth and hyphal formation. L. crispatus might repress the expression of hyphae-specific genes (ALS3, HWP1, and ECE1) in a NRG1-dependent manner. Besides, L. crispatus B145 is highly worthwhile for probiotic investigation.

Fungal interactions with the human host: exploring the spectrum of symbiosis

“…Initially it was suggested that antibiotic treatment removed lactobacilli from the vaginal mucosa, increasing vaginal pH, and promoting Candida hyphal formation. In agreement with this, lactobacilli have been proposed to reduce Candida colonisation [37], and have been explored as a potential probiotics [38]. However, other studies suggest that vaginal pH, and the lactobacilli population are not significantly altered in VVC [39], and that Candida colonisation is more common in women with a lactobacillus dominated microflora [40].…”

Vulvovaginal Candidiasis: A Current Understanding and Burning Questions

“…The metabolites of Lactobacillus spp. including organic acids, hydrogen peroxide, bacteriocins, and biosurfactants, all contribute to these antifungal effects [124,125]. However, only specific Lactobacillus strains are capable of producing these effectors in quantities required for antifungal activity, which possibly explains the failure of some vaginal lactobacilli to suppress Candida colonization.…”

“…In support of this, down-regulation of hypha-specific transcriptional regulatory genes (EFG1, BCR1, and CPH1, etc.) and virulence related genes (HWP1, ALS3, ECE1, and SAP5) were observed during co-culture with lactobacilli or treatment with spent culture supernatant [125,127]. Lactobacilli were also reported to compete with the attachment of C. albicans to host cells, resulting in reduced adhesion to epithelial surfaces [128].…”

Comparative Genomics of Lactobacillus crispatus from the Gut and Vagina Reveals Genetic Diversity and Lifestyle Adaptation

“…Numerous studies have shown the considerable probiotic potential of L. crispatus, such as modulating the host's immune system [2], reducing allergic symptoms in mice [3], down-regulating the expression of cancer genes, and inhibiting the proliferation of MDA-MB-231 breast cancer cell lines [4]. In addition, as one of the most detected Lactobacillus species in the healthy female vagina [5], L. crispatus can inhibit vaginal pathogenic microorganisms, and maintain the health of the female reproductive system [6][7][8]. Moreover, clinical trials have shown the therapeutic effect of L. crispatus on female vaginitis and recurrent urinary tract infection [9,10].…”