Optimization of Propidium Monoazide qPCR (Viability-qPCR) to Quantify the Killing by the Gardnerella-Specific Endolysin PM-477, Directly in Vaginal Samples from Women with Bacterial Vaginosis

Key bacterial vaginosis-associated bacteria influence each other's growth in biofilms in rich media and media simulating vaginal tract secretions

Bacterial vaginosis (BV) is a very common gynaecologic condition affecting women of reproductive age worldwide. BV is characterized by a depletion of lactic acid-producing Lactobacillus species and an increase in strict and facultative anaerobic bacteria that develop a polymicrobial biofilm on the vaginal epithelium. Despite multiple decades of research, the etiology of this infection is still not clear. However, some BV-associated bacteria (BVAB) may play a key role in the development of this infection, namely Gardnerella species, Prevotella bivia, and Fannyhessea vaginae. In this work, we aimed to characterize the growth of these three species in a rich medium and in a medium simulating vaginal tract secretions (mGTS). We first assessed planktonic growth in New York City (NYCIII) medium and mGTS and observed that the three species showed distinct capacities to grow in the two media. Surprisingly, despite the ability of all three species to grow in single-species in NYCIII, in a triple-species consortium P. bivia was not able to increase its concentration after 48 h, as assessed by qPCR. Furthermore, when using the more restrictive mGTS media, G. vaginalis was the only BVAB able to grow in the triple-species consortia. Interestingly, we found that P. bivia growth in NYCIII was influenced by the cell-free supernatant (CFS) of F. vaginae and by the CFS of G. vaginalis in mGTS. This antimicrobial activity appears to happen due to the acidification of the media. Single- and triple-species biofilms were then formed, and the growth of each species was further quantified by qPCR. While G. vaginalis had a high capacity to form biofilms in both media, F. vaginae and P. bivia biofilm growth was favored when cultured in rich media. Differences were also found in the structure of triple-species biofilms formed in both media, as assessed by confocal laser scanning microscopy. In conclusion, while all three species were able to grow in single-species biofilms in rich media, in mGTS the growth of G. vaginalis was essential for incorporation of the other species in the biofilm.

Prevalence and clinical correlates of Gardnerella spp., Fannyhessea vaginae, Lactobacillus crispatus and L. iners in pregnant women in Bukavu, Democratic Republic of the Congo

Background

Gardnerella is a key pathogen in bacterial vaginosis (BV), but the role of the different Gardnerella species remains unclear. We investigated the role of four Gardnerella species, as well as Fannyhessea vaginae, Lactobacillus crispatus and L. iners in BV.

Methods

From 331 pregnant women from the Democratic Republic of the Congo, BV was diagnosed using Nugent scoring and a cervicovaginal lavage was used to quantify G. leopoldii, G. piotii, G. swidsinskii, G. vaginalis, F. vaginae, L. crispatus and L. iners by qPCR. Univariate associations between these species and clinical outcomes were assessed. A logistic regression model and ROC curves were calculated to determine the best diagnostic marker for BV.

Results

Here, L. iners (75.8%) was the most prevalent species and G. vaginalis (36.0%) the most common Gardnerella species. All investigated Gardnerella spp. were prevalent (50.9-57.9%) in women with (asymptomatic) BV. Univariate analysis revealed no significant associations with clinical symptoms of BV, while F. vaginae (positive Whiff test, high pH), G. vaginalis (high pH) and L. crispatus (low pH) were associated with signs of BV. G. piotii was associated with markers of urinary tract infection. Women with L. iners had higher odds of delivering preterm. ROC analyses showed that F. vaginae was the best marker for BV (AUC 0.81), and the combined model further increased the diagnostic performance (AUC 0.90).

Conclusion

All Gardnerella species were involved in BV, although none were associated with the most important clinical symptoms of BV and none emerged as a superior molecular marker for BV.

Development and validation of a PMA-qPCR method for accurate quantification of viable Lacticaseibacillus paracasei in probiotics

The effectiveness of probiotic products hinges on the viability and precise quantification of probiotic strains. This study addresses this crucial requirement by developing and validating a precise propidium monoazide combination with quantitative polymerase chain reaction (PMA-qPCR) method for quantifying viable Lacticaseibacillus paracasei in probiotic formulations. Initially, species-specific primers were meticulously designed based on core genes from the whole-genome sequence (WGS) of L. paracasei, and they underwent rigorous validation against 462 WGSs, 25 target strains, and 37 non-target strains across various taxonomic levels, ensuring extensive inclusivity and exclusivity. Subsequently, optimal PMA treatment conditions were established using 25 different L. paracasei strains to effectively inhibit dead cell DNA amplification while preserving viable cells. The developed method exhibited a robust linear relationship (R 2 = 0.994) between cycle threshold (Cq) values and viable cell numbers ranging from 103 to 108 CFU/mL, with an impressive amplification efficiency of 104.48% and a quantification limit of 7.30 × 103 CFU/mL. Accuracy assessments revealed biases within ±0.5 Log10 units, while Bland-Altman analysis demonstrated a mean bias of 0.058 Log10, with 95% confidence limits of -0.366 to 0.482 Log10. Furthermore, statistical analysis (p = 0.76) indicated no significant differences between theoretical and measured values. This validated PMA-qPCR method serves as a robust and accurate tool for quantifying viable L. paracasei in various sample matrices, including pure cultures, probiotics as food ingredients, and composite probiotic products, thereby enhancing probiotic product quality assurance and contributing to consumer safety and regulatory compliance.

In vitro bacterial vaginosis biofilm community manipulation using endolysin therapy

Bacterial vaginosis (BV) affects approximately 26% of women of childbearing age globally, presenting with 3-5 times increased risk of miscarriage and two-fold risk of pre-term birth. Antibiotics (metronidazole and clindamycin) are typically employed to treat BV; however the success rate is low due to the formation of recalcitrant polymicrobial biofilms. As a novel therapeutic, promising results have been obtained in vitro using Gardnerella endolysins, although to date their efficacy has only been demonstrated against simple biofilm models. In this study, a four-species biofilm was developed consisting of Gardnerella vaginalis, Fannyhessea vaginae, Prevotella bivia and Mobiluncus curtisii. Biofilms were grown in NYC III broth and treated using antibiotics and an anti-Gardnerella endolysin (CCB7.1) for 24 h. Biofilm composition, viability and structure were assessed using colony counts, live/dead qPCR and scanning electron microscopy. All species colonised biofilms to varying degrees, with G. vaginalis being the most abundant. Biofilm composition remained largely unchanged when challenged with escalated concentrations of conventional antibiotics. A Gardnerella-targeted endolysin candidate (CCB7.1) showed efficacy against several Gardnerella species planktonically, and significantly reduced viable G. vaginalis within polymicrobial biofilms at 1 to 4X pMIC (p < 0.05 vs. vehicle control). Collectively, this study highlights the resilience of biofilm-embedded pathogens against the currently used antibiotics and provides a polymicrobial model that allows for more effective pre-clinical screening of BV therapies. The Gardnerella-specific endolysin CCB7.1 demonstrated significant activity against G. vaginalis within polymicrobial biofilms, altering the overall community dynamic and composition.

Six Bacterial Vaginosis-Associated Species Can Form an In Vitro and Ex Vivo Polymicrobial Biofilm That Is Susceptible to Thymbra capitata Essential Oil

Bacterial vaginosis (BV) is associated with serious gynaecologic and obstetric complications. The hallmark of BV is the presence of a polymicrobial biofilm on the vaginal epithelium, but BV aetiology is still a matter of debate. We have previously developed an in vitro biofilm model that included three BV-associated species, but, up to now, no studies are available whereby more bacterial species are grown together to better mimic the in vivo situation. Herein, we characterized the first polymicrobial BV biofilm consisting of six cultivable BV-associated species by using both in vitro and ex vivo vaginal tissue models. Both models revealed that the six species were able to incorporate the polymicrobial biofilm, at different bacterial concentrations. As it has been thought that this polymicrobial biofilm may increase the survival of BV-associated species when exposed to antibiotics, we also assessed if the Thymbra capitata essential oil (EO), which has recently been shown to be highly bactericidal against several Gardnerella species, could maintain its anti-biofilm activity against this polymicrobial biofilm. Under our experimental conditions, T. capitata EO exhibited a high antibacterial effect against polymicrobial biofilms, in both tested models, with a significant reduction in the biofilm biomass and the number of culturable cells. Overall, this study shows that six BV-associated species can grow together and form a biofilm both in vitro and when using an ex vivo model. Moreover, the data obtained herein should be considered in further applications of T. capitata EO as an antimicrobial agent fighting BV.

Exploiting the Anti-Biofilm Effect of the Engineered Phage Endolysin PM-477 to Disrupt In Vitro Single- and Dual-Species Biofilms of Vaginal Pathogens Associated with Bacterial Vaginosis

Bacterial vaginosis (BV) is the most frequent vaginal infection in women of reproductive age. It is caused by the overgrowth of anaerobic vaginal pathogens, such as Gardnerella vaginalis, Fannyhessea vaginae, and Prevotella bivia, which are vaginal pathogens detected during the early stages of incident BV and have been found to form multi-species biofilms. Treatment of biofilm-associated infections, such as BV, is challenging. In this study, we tested the role of an investigational engineered phage endolysin, PM-477, in the eradication of dual-species biofilms composed of G. vaginalis–F. vaginae or G. vaginalis–P. bivia. Single-species biofilms formed by these species were also analysed as controls. The effect of PM-477 on biomass and culturability of single- and dual-species biofilms was assessed in vitro using a microtiter plate assay, epifluorescence microscopy, confocal laser scanning microscopy, and quantitative PCR. The results showed that PM-477 was particularly effective in the disruption and reduction of culturability of G. vaginalis biofilms. In dual-species biofilms, PM-477 exhibited lower efficiency but was still able to selectively and significantly eliminate G. vaginalis. Since polymicrobial interactions have been shown to strongly affect the activity of various antibiotics, the activity of PM-477 in dual-species biofilms is a potentially promising result that should be further explored, aiming to completely eradicate multi-species biofilms associated with BV.