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