Biotypes and virulence factors of Gardnerella vaginalis isolated from cases of bacterial vaginosis

Under conditions closely mimicking vaginal fluid, Lactobacillus jensenii strain 62B produces a bacteriocin-like inhibitory substance that targets and eliminates Gardnerella species

Within the vaginal ecosystem, lactobacilli and Gardnerella spp. likely interact and influence each other's growth, yet the details of this interaction are not clearly defined. Using medium simulating vaginal fluid and a two-chamber co-culturing system to prevent cell-to-cell contact between the bacteria, we examined the possibility that Lactobacillus jensenii 62B (Lj 62B) and/or G. piotii (Gp) JCP8151B produce extracellular factors through which they influence each other's viability. By 24 h post-inoculation (hpi) in the co-culture system and under conditions similar to the vaginal environment - pH 5.0, 37 °C, and 5% CO2, Lj 62B viability was not affected but Gp JCP8151B had been eliminated. Cell-free supernatant harvested from Lj 62B cultures (Lj-CFS) at 20 hpi, but not 16 hpi, also eliminated Gp JCP8151B growth. Neither lactic acid nor H2O2 production by Lj 62B was responsible for this effect. The Lj-CFS did not affect viability of three species of lactobacilli or eight species of Gram-positive and Gram-negative uropathogens but eliminated viability of eight different strains of Gardnerella spp. Activity of the inhibitory factor within Lj-CFS was abolished by protease treatment and reduced by heat treatment suggesting it is most likely a bacteriocin-like protein; fractionation revealed that the factor has a molecular weight within the 10-30 kDa range. These results suggest that, in medium mimicking vaginal fluid and growth conditions similar to the vaginal environment, Lj 62B produces a potential bacteriocin-like inhibitory substance (Lj-BLIS) that clearly targets Gardnerella spp. strains. Once fully characterized, Lj-BLIS may be a potential treatment for Gardnerella-related BV that does not alter the vaginal microflora.

Gardnerella Revisited: Species Heterogeneity, Virulence Factors, Mucosal Immune Responses, and Contributions to Bacterial Vaginosis

Gardnerella species are associated with bacterial vaginosis (BV) and have been investigated as etiological agents of the condition. Nonetheless, the isolation of this taxon from healthy individuals has raised important questions regarding its etiological role. Recently, using advanced molecular approaches, the Gardnerella genus was expanded to include several different species that exhibit differences in virulence potential. Understanding the significance of these different species with respect to mucosal immunity and the pathogenesis and complications of BV could be crucial to solving the BV enigma. Here, we review key findings regarding the unique genetic and phenotypic diversity within this genus, virulence factors, and effects on mucosal immunity as they stand. We also comment on the relevance of these findings to the proposed role of Gardnerella in BV pathogenesis and in reproductive health and identify key gaps in knowledge that should be explored in the future.

Prognosis of recurrent bacterial vaginosis based on longitudinal changes in abundance of Lactobacillus and specific species of Gardnerella

Refractory responses to standard-of-care oral metronidazole among recurrent bacterial vaginosis (BV) patients is not rare, and recurrence within a year is common. A better understanding of the bacterial determinants of these outcomes is essential. In this study we ask whether changes in specific species of Gardnerella are associated with poor short or long term clinical outcomes, and if and how resurgence of Lactobacillus species affects these outcomes. We quantify Lactobacillus isolates as a proportion of total vaginal bacteria using the LbRC5 qPCR assay, and 5 prevalent species of Gardnerella using primers that target species-specific polymorphisms within the cpn60 gene. The study includes 43 BV patients: 18 refractory, 16 recurrent, and 11 remission patients, sampled daily for up to two weeks post-treatment; clinical outcomes were tracked for up to 9 months. Persistently high titers of Gardnerella Gsp07 were associated with refractory responses, and persistently low abundance of Gardnerella Gsp07 and G. swidsinskii / G. leopoldii were associated with remission. Lactobacillus species abundance rose in 4-14 days after initiation of treatment in most but not all recurrent and remission patients, although increases were more sustained among remission patients. The findings suggest that Gardnerella Gsp07 and G. swidsinskii / G. leopoldii are markers of poor clinical outcome or may directly or indirectly suppress recovery of Lactobacillus species, thereby interfering with clinical recovery. Therapies that target these strains may improve patient outcome.

The Female Vaginal Microbiome in Health and Bacterial Vaginosis

The vaginal microbiome is an intricate and dynamic microecosystem that constantly undergoes fluctuations during the female menstrual cycle and the woman's entire life. A healthy vaginal microbiome is dominated by Lactobacillus which produce various antimicrobial compounds. Bacterial vaginosis (BV) is characterized by the loss or sharp decline in the total number of Lactobacillus and a corresponding marked increase in the concentration of anaerobic microbes. BV is a highly prevalent disorder of the vaginal microbiota among women of reproductive age globally. BV is confirmed to be associated with adverse gynecologic and obstetric outcomes, such as sexually transmitted infections, pelvic inflammatory disease, and preterm birth. Gardnerella vaginalis is the most common microorganism identified from BV. It is the predominant microbe in polymicrobial biofilms that could shelter G. vaginalis and other BV-associated microbes from adverse host environments. Many efforts have been made to increase our understanding of the vaginal microbiome in health and BV. Thus, improved novel and accurate diagnosis and therapeutic strategies for BV have been developed. This review covers the features of vaginal microbiome, BV, BV-associated diseases, and various strategies of diagnosis and treatment of BV, with an emphasis on recent research progresses.

Comparative analysis of virulence factors & biotypes of Gardnerella vaginalis isolated from the genital tract of women with & without bacterial vaginosis

Background & objectives

: Bacterial vaginosis (BV) involves the presence of a thick vaginal multispecies biofilm, where Gardnerella vaginalis is the predominant species. The reason for an increase in the number of G. vaginalis which are usually present as normal flora of the female genital tract in cases of BV, is not known. Hence, the objective of the present study was to compare the biotypes and virulence factors of G. vaginalis isolated from the genital tract of women with and without BV.

Methods

: High vaginal swabs collected from 811 women of reproductive age were cultured. G. vaginalis isolates were biotyped and tested for adherence to vaginal epithelial cells, biofilm formation, agglutination of human red blood cells (RBCs), protease production, phospholipase production and surface hydrophobicity.

Results

: Of the isolates from women with BV, 83.3 per cent (60/72) showed good adherence, 78.4 per cent (58/74) produced biofilm, 82.9 per cent (63/76) produced phospholipase, 67.1 per cent (51/76) produced protease, 77.3 per cent (58/75) were positive for surface hydrophobicity and 61.6 per cent (45/73) were positive for haemagglutination of human RBC. In case of G. vaginalis from non-BV women, 25 per cent (15/60) isolates showed good adherence, 18.4 per cent (9/49) biofilm production, 35 per cent (21/60) phospholipase, 36.6 per cent (22/60) protease, 41.7 per cent (25/60) surface hydrophobicity and 10.1 per cent (6/59) agglutination of human RBCs. Maximum number of isolates belonged to biotypes 6, 2 and 3. Biotype 3 was more associated with non-BV rather than BV; biotype 6, 2 and 1 were more associated with cases of BV. Maximum virulence factors were expressed by biotypes 6, 2 and 1.

Interpretation & conclusions

: Virulence factors were more expressed by G. vaginalis isolates obtained from women with BV rather than from non-BV. Biotypes 6, 2 and 1 were more associated with cases of BV and expressed maximum virulence factors.

Prevalence of vaginolysin, sialidase and phospholipase genes in Gardnerella vaginalis isolates between bacterial vaginosis and healthy individuals

Background: Gardnerella vaginalis is considered as the predominant microorganism found in bacterial vaginosis (BV). The aim of this study was to evaluate the prevalence of virulence factors in G. vaginalis associated with BV or non-BV cases and their correlations with this disorder. Methods: A total of 102 vaginal specimens were collected from patients during their visit to Akbar Abadi hospital in Tehran, Iran. Bacterial vaginosis was determined by Nugent score and Amsel's criteria. Polymerase chain reaction (PCR) was used for the detection of G. vaginalis 16S rRNA, vaginolysin, sialidase and phospholipase genes. To evaluate the association between the presence of vly, pho, and sld genes and BV. Pearson Chi-square test was applied using SPSS software. P-value ≤0.05 was considered as significant. Results: Totally, 27.4% of the patients were suffering from BV. Gardnerella vaginalis was found in 100% women with BV and in 56.7% women with normal vaginal discharge. The prevalence of vly, sld and pho genes in BV-associated G. vaginalis was 10 (35.7%) (95% CI [0.18, 0.53]), 19 (67.8%) (95% CI [0.51, 0.85]) and 6 (21.4%) (95% CI [0.06, 0.37]), respectively. The prevalence of the aforementioned genes in non-BV associated G. vaginalis was 20 (47.6%) (95% CI [0.33, 0.63]), 28 (66.6%) (95% CI [0.52, 0.81]), and 5 (11.9%) (95% CI [0.02, 0.22]), respectively. Our results showed no statistically significant association between the presence of the virulence genes and BV associatedness of this microorganism. Conclusion: Our results showed the presence of G. vaginalis in all BV patients and relatively high prevalence in healthy individuals. The prevalence rates of the three virulence genes were different in BV and non-BV associated G. vaginalis; however, the differences were not statistically significant.

Quantitation of all Four Gardnerella vaginalis Clades Detects Abnormal Vaginal Microbiota Characteristic of Bacterial Vaginosis More Accurately than Putative G. vaginalis Sialidase A Gene Count

Background

Bacterial vaginosis (BV) is a vaginal disorder characterized by a depletion of the normal lactobacillus-dominant microbiota and overgrowth of mainly anaerobic bacteria.

Objectives

The study aimed to evaluate the distribution and abundance of the Gardnerella vaginalis clades and sialidase A gene in vaginal samples from Russian women, and investigate if the G. vaginalis sialidase A gene count detects an abnormal vaginal microbiota characteristic of BV more accurately than G. vaginalis load.

Methods

Vaginal samples from 299 non-pregnant patients of gynecological clinics were examined using Nugent scores and G. vaginalis clade and sialidase A gene quantitative real-time polymerase chain reactions (PCRs). Discriminatory power for BV microbiota was evaluated with receiver operating characteristic (ROC) analysis.

Results

The vaginal microbiota was characterized by Nugent scores as normal, intermediate, and BV microbiota in 162, 58, and 79 women, respectively. G. vaginalis clades 1, 2, 3, 4, and the sialidase A gene were detected in 56% (51–62%), 40% (34–45%), 20% (16–25%), 94% (91–96%), and 70% (64–75%) of vaginal samples, respectively. The frequency and abundance of clades 1, 2, 4, and the sialidase A gene as well as clade multiplicity were significantly associated with abnormal microbiota. The sialidase A gene was present in all multi-clade samples, in all single-clade samples comprising clades 1, 2, and 3, and in four of 84 (5% [2–12%]) samples comprising clade 4 only. Total G. vaginalis load showed significantly higher discriminatory power for abnormal microbiota than sialidase A gene count (areas under ROC curves 0.933 vs. 0.881; p = 0.0306).

Conclusions

Quantifying all four G. vaginalis clades discriminates between BV microbiota and normal microbiota more accurately than measuring G. vaginalis sialidase A gene. Clade 4 is strongly associated with BV microbiota, despite most clade 4 strains lacking the sialidase A gene.

Etiology of bacterial vaginosis and polymicrobial biofilm formation

Microorganisms in nature rarely exist in a planktonic form, but in the form of biofilms. Biofilms have been identified as the cause of many chronic and persistent infections and have been implicated in the etiology of bacterial vaginosis (BV). Bacterial vaginosis is the most common form of vaginal infection in women of reproductive age. Similar to other biofilm infections, BV biofilms protect the BV-related bacteria against antibiotics and cause recurrent BV. In this review, an overview of BV-related bacteria, conceptual models and the stages involved in the polymicrobial BV biofilm formation will be discussed.

Anaerobes and bacterial vaginosis in pregnancy: virulence factors contributing to vaginal colonisation

The aetiology and pathogenesis of bacterial vaginosis (BV) is unclear but it appears to be associated with factors that disrupt the normal acidity of the vagina thus altering the equilibrium between the normal vaginal microbiota. BV has serious implications for female morbidity, including reports of pelvic inflammatory disease, adverse pregnancy outcomes, increased susceptibility to sexually transmitted infections and infertility. This paper reviewed new available information regarding possible factors contributing to the establishment of the BV vaginal biofilm, examined the proposed role of anaerobic microbial species recently detected by new culture-independent methods and discusses developments related to the effects of BV on human pregnancy. The literature search included Pubmed (NLM), LISTA (EBSCO), and Web of Science. Because of the complexity and diversity of population groups, diagnosis and methodology used, no meta-analysis was performed. Several anaerobic microbial species previously missed in the laboratory diagnosis of BV have been revealed while taking cognisance of newly proposed theories of infection, thereby improving our understanding and knowledge of the complex aetiology and pathogenesis of BV and its perceived role in adverse pregnancy outcomes.

Identification, quantification and subtyping of Gardnerella vaginalis in noncultured clinical vaginal samples by quantitative PCR

Gardnerella vaginalis is an important component of the human vaginal microflora. It is proposed to play a key role in the pathogenesis of bacterial vaginosis (BV), the most common vaginal condition. Here we describe the development, validation and comparative analysis of a novel molecular approach capable of G. vaginalis identification, quantification and subtyping in noncultured vaginal specimens. Using two quantitative PCR (qPCR) assays, we analysed G. vaginalis bacterial loads and clade distribution in 60 clinical vaginal-swab samples. A very high pathogen prevalence was revealed by species-specific qPCR not only among BV patients (100 %), but also in healthy women (97 %), although the G. vaginalis concentration was significantly lower in non-BV samples. G. vaginalis clades identified in vaginal specimens by subtyping multiplex qPCR, which targets four clade-specific genetic markers, had frequencies of 53 % for clade 1, 25 % for clade 2, 32 % for clade 3 and 83 % for clade 4. Multiple clades were found in 70 % of samples. Single G. vaginalis clades were represented by clade 1 and clade 4 in 28 % of specimens. A positive association with BV was shown for clade 1 and clade 3, while clade 2 was positively associated with intermediate vaginal microflora, but not with BV. Clade 4 demonstrated no correlation with the disorder. The presence of multiple clades had a high positive association with BV, whereas G. vaginalis identified as a single clade was negatively linked with the condition. Polyclonal G. vaginalis infection may be a risk factor for BV.

Fluorescence in situ Hybridization method using Peptide Nucleic Acid probes for rapid detection of Lactobacillus and Gardnerella spp

BACKGROUND

Bacterial vaginosis (BV) is a common vaginal infection occurring in women of reproductive age. It is widely accepted that the microbial switch from normal microflora to BV is characterized by a decrease in vaginal colonization by Lactobacillus species together with an increase of Gardnerella vaginalis and other anaerobes. Our goal was to develop and optimize a novel Peptide Nucleic Acid (PNA) Fluorescence in situ Hybridization assay (PNA FISH) for the detection of Lactobacillus spp. and G. vaginalis in mixed samples.

RESULTS

Therefore, we evaluated and validated two specific PNA probes by using 36 representative Lactobacillus strains, 22 representative G. vaginalis strains and 27 other taxonomically related or pathogenic bacterial strains commonly found in vaginal samples. The probes were also tested at different concentrations of G. vaginalis and Lactobacillus species in vitro, in the presence of a HeLa cell line. Specificity and sensitivity of the PNA probes were found to be 98.0% (95% confidence interval (CI), from 87.8 to 99.9%) and 100% (95% CI, from 88.0 to 100.0%), for Lactobacillus spp.; and 100% (95% CI, from 92.8 to 100%) and 100% (95% CI, from 81.5 to 100.0%) for G. vaginalis. Moreover, the probes were evaluated in mixed samples mimicking women with BV or normal vaginal microflora, demonstrating efficiency and applicability of our PNA FISH.

CONCLUSIONS

This quick method accurately detects Lactobacillus spp. and G. vaginalis species in mixed samples, thus enabling efficient evaluation of the two bacterial groups, most frequently encountered in the vagina.

Clinical features of bacterial vaginosis in a murine model of vaginal infection with Gardnerella vaginalis

Bacterial vaginosis (BV) is a dysbiosis of the vaginal flora characterized by a shift from a Lactobacillus-dominant environment to a polymicrobial mixture including Actinobacteria and Gram-negative bacilli. BV is a common vaginal condition in women and is associated with increased risk of sexually transmitted infection and adverse pregnancy outcomes such as preterm birth. Gardnerella vaginalis is one of the most frequently isolated bacterial species in BV. However, there has been much debate in the literature concerning the contribution of G. vaginalis to the etiology of BV, since it is also present in a significant proportion of healthy women. Here we present a new murine vaginal infection model with a clinical isolate of G. vaginalis. Our data demonstrate that this model displays key features used clinically to diagnose BV, including the presence of sialidase activity and exfoliated epithelial cells with adherent bacteria (reminiscent of clue cells). G. vaginalis was capable of ascending uterine infection, which correlated with the degree of vaginal infection and level of vaginal sialidase activity. The host response to G. vaginalis infection was characterized by robust vaginal epithelial cell exfoliation in the absence of histological inflammation. Our analyses of clinical specimens from women with BV revealed a measureable epithelial exfoliation response compared to women with normal flora, a phenotype that, to our knowledge, is measured here for the first time. The results of this study demonstrate that G. vaginalis is sufficient to cause BV phenotypes and suggest that this organism may contribute to BV etiology and associated complications. This is the first time vaginal infection by a BV associated bacterium in an animal has been shown to parallel the human disease with regard to clinical diagnostic features. Future studies with this model should facilitate investigation of important questions regarding BV etiology, pathogenesis and associated complications.

Comparative genomic analyses of 17 clinical isolates of Gardnerella vaginalis provide evidence of multiple genetically isolated clades consistent with subspeciation into genovars

Gardnerella vaginalis is associated with a spectrum of clinical conditions, suggesting high degrees of genetic heterogeneity among stains. Seventeen G. vaginalis isolates were subjected to a battery of comparative genomic analyses to determine their level of relatedness. For each measure, the degree of difference among the G. vaginalis strains was the highest observed among 23 pathogenic bacterial species for which at least eight genomes are available. Genome sizes ranged from 1.491 to 1.716 Mb; GC contents ranged from 41.18% to 43.40%; and the core genome, consisting of only 746 genes, makes up only 51.6% of each strain's genome on average and accounts for only 27% of the species supragenome. Neighbor-grouping analyses, using both distributed gene possession data and core gene allelic data, each identified two major sets of strains, each of which is composed of two groups. Each of the four groups has its own characteristic genome size, GC ratio, and greatly expanded core gene content, making the genomic diversity of each group within the range for other bacterial species. To test whether these 4 groups corresponded to genetically isolated clades, we inferred the phylogeny of each distributed gene that was present in at least two strains and absent in at least two strains; this analysis identified frequent homologous recombination within groups but not between groups or sets. G. vaginalis appears to include four nonrecombining groups/clades of organisms with distinct gene pools and genomic properties, which may confer distinct ecological properties. Consequently, it may be appropriate to treat these four groups as separate species.