Lactic acid bacteria are considered an inexhaustible source of bioactive compounds; indeed, products from their metabolism are known to have immunomodulatory and anti-inflammatory activity. Recently, we demonstrated that Cell-Free Supernatants (CFS) obtained from Lactobacillus (L.) acidophilus, Lactiplantibacillus (L.) plantarum, Lacticaseibacillus (L.) rhamnosus, and Limosilactobacillus (L.) reuteri can impair Candida pathogenic potential in an in vitro model of epithelial vaginal infection. This effect could be ascribed to a direct effect of living lactic acid bacteria on Candida virulence and to the production of metabolites that are able to impair fungal virulence. In the present work, stemming from these data, we deepened our knowledge of CFS from these four lactic acid bacteria by performing a metabolomic analysis to better characterize their composition. By using an untargeted metabolomic approach, we detected consistent differences in the metabolites produced by these four different lactic acid bacteria. Interestingly, L. rhamnosus and L. acidophilus showed the most peculiar metabolic profiles. Specifically, after a hierarchical clustering analysis, L. rhamnosus and L. acidophilus showed specific areas of significantly overexpressed metabolites that strongly differed from the same areas in other lactic acid bacteria. From the overexpressed compounds in these areas, inosine from L. rhamnosus returned with the best identification profile. This molecule has been described as having antioxidant, anti-inflammatory, anti-infective, and neuroprotective properties. The biological significance of its overproduction by L. rhamnosus might be important in its probiotic and/or postbiotic activity.

Antimicrobial peptides represent a promising alternative to traditional drugs in relation to cost, toxicity, and, primarily, the growing problem of drug resistance. Here, we report on the activity against HSV-1 and HSV-2 of a previously described wide-spectrum synthetic decapeptide, Killer Peptide (KP). As determined by plaque reduction assays, treatment with KP at 100 μg/mL resulted in a reduction in the viral yield titer of 3.5 Logs for HSV-1 and 4.1 Logs for HSV-2. Further evaluation of KP antiviral activity focused on the early stages of the virus replicative cycle, including the determination of the residual infectivity of viral suspensions treated with KP. A direct effect of the peptide on viral particles impairing virus absorption and penetration was shown. The toxicity profile proved to be extremely good, with a selectivity index of 29.6 for HSV-1 and 156 for HSV-2. KP was also active against acyclovir (ACV)-resistant HSV isolates, while HSV subcultures in the presence of sub-inhibitory doses of KP did not lead to the emergence of resistant strains. Finally, the antiviral action of KP proved to be synergistic with that of ACV. Overall, these results demonstrate that KP could represent an interesting addition/alternative to acyclovir for antiviral treatment.

Lactobacilli are considered an inexhaustible source of potentially bioactive substances; indeed, several products from their metabolism are known to have immunomodulatory and anti-inflammatory activity. Recently, we demonstrated that cell-free supernatants (CFS) obtained from Lactobacillus (L.) acidophilus, L. plantarum, L. rhamnosus and L. reuteri can impair Candida pathogenic potential in an in vitro model of epithelial vaginal infection. This effect could be ascribed to a direct effect of living lactobacilli on Candida virulence and to the production of metabolites which are able to impair fungal virulence. In the present work, stemming from those data, we deepened our knowledge on the CFS from these 4 lactobacilli by performing a metabolomic analysis to better characterize their composition. By using an untargeted metabolomic approach, we detected consistent differences in the metabolites produced by these four different lactobacilli. Interestingly, L. rhamnosus showed the most peculiar metabolic profile. Specifically, after a hierarchical clustering analysis in positive and negative ionization mode, L. rhamnosus showed a specific area of significant overexpressed metabolites that strongly differed from the same area in other lactobacilli. In this area, inosine was identified among the overexpressed metabolites of L. rhamnosus. This molecule has been described to have antioxidant, anti-inflammatory, anti-infective and neuroprotective properties. The biological significance of its overproduction by L. rhamnosus might be important in its probiotic and/or postbiotic activity.

Little is known about the complex events driving host–pathogen and pathogen–pathogen interplay in polymicrobial infections. Using an in vitro model of a reconstituted vaginal epithelium (RVE) employing the A-431 cell line supplemented with synthetic vaginal fluid (SVF), we studied the consequences of single versus dual infections with Candida albicans and/or Herpes Simplex Virus-2 (HSV-2). Our data show (a) a relevant, SVF-enhanced expression of the differentiation marker cytokeratin 5/6 in the RVE; (b) the ability of Candida albicans to enhance HSV-2 in the dual infection model, with the virus titer almost doubling in the presence of SVF; (c) RVE damage (>20%), mostly attributable to Candida albicans and related to oxidative stress whether SVF is present; (d) the dysregulation of mucin-1, the production of which is enhanced (from 13 to 21 ng/mL) or impaired (from 21 to 10 ng/mL) in response to either SVF or infection, respectively; and (e) a partial-to-negligible cytokine response from the RVE, depending upon SVF presence. In conclusion, using an in vitro RVE model upgraded through the addition of synthetic vaginal fluid, we provide details on epithelial cell–pathogen–pathogen interaction, contributing to a better comprehension of the pathogenesis of polymicrobial infections at a mucosal level.

Antimicrobial peptides represent a promising alternative to traditional drugs in relation to cost, toxicity and, primarily, the growing problem of drug resistance. Here we report on the activity against HSV-1 and HSV-2 of a previously described wide-spectrum synthetic decapeptide, Killer Peptide (KP). As determined by plaque reduction assays, treatment with KP at 100 μg/mL resulted in a reduction in the viral yield titer of 3.5 Logs for HSV-1 and 4.1 Logs for HSV-2. Further evaluation of KP antiviral activity focused on the early stages of virus replicative cycle, including the determination of the residual infectivity of viral suspensions treated with KP. A direct effect of the peptide on viral particles, impairing virus absorption and penetration, was shown. The toxicity profile proved to be extremely good with a selectivity index of 29.6 for HSV-1 and 156 for HSV-2. KP was also active against an acyclovir (ACV)-resistant HSV-1 strain, while HSV-1 subcultures in the presence of sub-inhibitory doses of KP did not lead to the emergence of resistant strains. Finally, the antiviral action of KP proved to be synergistic with that of ACV. Overall, these results demonstrate that KP could represent an interesting addition/alternative to acyclovir for antiviral treatment.

Candida albicans (C. albicans) is a commensal of the vaginal mucosa and the main etiological agent of acute and recurrent vulvovaginal candidiasis (VVC/RVVC). Disease severity is thought to depend on a dysregulated host inflammatory response to Candida, not necessarily associated with increased fungal burden and/or morphogenesis. The role of strain-specific differences leading to epithelial immune response or tolerance remains undefined. In this study, we compared the virulence profile of vaginal C. albicans isolates from women with acute VVC/RVVC (VVC/RVVC), asymptomatic colonizer (Colonizing), and VVC/RVVC associated with microbial co-infections (Co-infections). Isolates were evaluated for growth and biofilm formation under standard culture conditions and tested in an in vitro vaginal epithelial cell (VEC) infection model to assess fungal shedding, epithelial damage, and cytokine production. Corresponding vaginal samples were analyzed for C. albicans morphology, polymorphonuclear neutrophil presence, microbiota composition, cytokines levels, and anti-C. albicans IgA production. No significant differences in growth or biofilm formation were observed among isolates under culture conditions. However, VEC infection revealed strain-dependent differences: acute VVC/RVVC and Co-infections isolates induced greater fungal shedding, while VVC/RVVC isolates caused increased epithelial damage and showed a trend toward higher cytokine production. Vaginal samples from symptomatic groups displayed increased neutrophils, hyphal morphology, elevated IL-1α, IL-1β, and anti-Candida IgA, but not IL-1Ra, without differences in lactobacilli abundance or Community-State-Type (CST) distribution. These findings suggest that C. albicans pathogenicity in VVC depends on strain-specific interactions with VEC driving differential host responses.