Biosynthesis and degradation of H2O2 by vaginal lactobacilli

Vaginal pH and microbicidal lactic acid when lactobacilli dominate the microbiota

Lactic acid at sufficiently acidic pH is a potent microbicide, and lactic acid produced by vaginal lactobacilli may help protect against reproductive tract infections. However, previous observations likely underestimated healthy vaginal acidity and total lactate concentration since they failed to exclude women without a lactobacillus-dominated vaginal microbiota, and also did not account for the high carbon dioxide, low oxygen environment of the vagina. Fifty-six women with low (0-3) Nugent scores (indicating a lactobacillus-dominated vaginal microbiota) and no symptoms of reproductive tract disease or infection, provided a total of 64 cervicovaginal fluid samples using a collection method that avoided the need for sample dilution and rigorously minimized aerobic exposure. The pH of samples was measured by microelectrode immediately after collection and under a physiological vaginal concentration of CO2. Commercial enzymatic assays of total lactate and total acetate concentrations were validated for use in CVF, and compared to the more usual HPLC method. The average pH of the CVF samples was 3.5 ± 0.3 (mean ± SD), range 2.8-4.2, and the average total lactate was 1.0% ± 0.2% w/v; this is a five-fold higher average hydrogen ion concentration (lower pH) and a fivefold higher total lactate concentration than in the prior literature. The microbicidal form of lactic acid (protonated lactic acid) was therefore eleven-fold more concentrated, and a markedly more potent microbicide, than indicated by prior research. This suggests that when lactobacilli dominate the vaginal microbiota, women have significantly more lactic acid-mediated protection against infections than currently believed. Our results invite further evaluations of the prophylactic and therapeutic actions of vaginal lactic acid, whether provided in situ by endogenous lactobacilli, by probiotic lactobacilli, or by products that reinforce vaginal lactic acid.

Development of a carbohydrate-supplemented semidefined medium for the semiselective cultivation of Lactobacillus spp

The macronutrient and micronutrient compositions of traditional media used to cultivate Lactic Acid Bacteria (LAB) are largely undefined, which precludes their use in many metabolic bioassays. In order to address this deficiency, we developed MS: a carbohydrate-supplemented semidefined medium with low-background coloration. MS was designed to support the semiselective cultivation of a wide range of fastidious species belonging to the Lactobacillus clade of the LAB. When supplemented with 100 mM D-glucose, the MS medium stimulated the proliferation of 21 strains of LAB, including Pediococcus spp. and Lactobacillus spp. The MS medium supported biomass accumulation comparable with MRS, an undefined medium routinely used for the cultivation of lactobacilli. Interestingly, however, the novel MS medium exhibited greater semiselectivity against non-LAB than MRS. Together, these results suggest that MS is an acceptable alternative to MRS for use in metabolic and phenotypic bioassays that use a colorimetric reporter system or would benefit from a semidefined nutrient composition.

Genomic and phenotypic evidence for probiotic influences of Lactobacillus gasseri on human health

Certain lactic acid bacteria (LAB) have the capacity to occupy mucosal niches of humans, including the oral cavity, gastrointestinal tract, and vagina. Among commensal, LAB are species of the acidophilus complex, which have proven to be a substantial reservoir for microorganisms with probiotic attributes. Specifically, Lactobacillus gasseri is an autochthonous microorganism which has been evaluated for probiotic activity based on the availability of genome sequence and species-specific adaptation to the human mucosa. Niche-related characteristics of L. gasseri contributing to indigenous colonization include tolerance of low pH environments, resistance to bile salts, and adhesion to the host epithelium. In humans, L. gasseri elicits various health benefits through its antimicrobial activity, bacteriocin production, and immunomodulation of the innate and adaptive systems. The genomic and empirical evidence supporting use of L. gasseri in probiotic applications is substantiated by clinical trial data displaying maintenance of vaginal homeostasis, mitigation of Helicobacter pylori infection, and amelioration of diarrhea.

Longitudinal qPCR study of the dynamics of L. crispatus, L. iners, A. vaginae, (sialidase positive) G. vaginalis, and P. bivia in the vagina

BACKGROUND

To obtain more detailed understanding of the causes of disturbance of the vaginal microflora (VMF), a longitudinal study was carried out for 17 women during two menstrual cycles.

METHODS

Vaginal swabs were obtained daily from 17 non-pregnant, menarchal volunteers. For each woman, Gram stains were scored, the quantitative changes of 5 key vaginal species, i.e. Atopobium vaginae, Lactobacillus crispatus, L. iners, (sialidase positive) Gardnerella vaginalis and Prevotella bivia were quantified with qPCR and hydrogen-peroxide production was assessed on TMB+ agar.

RESULTS

Women could be divided in 9 subjects with predominantly normal VMF (grades Ia, Ib and Iab, group N) and 8 with predominantly disturbed VMF (grades I-like, II, III and IV, group D). VMF was variable between women, but overall stable for most of the women. Menses were the strongest disturbing factor of the VMF. L. crispatus was present at log7-9 cells/ml in grade Ia, Iab and II VMF, but concentrations declined 100-fold during menses. L. crispatus below log7 cells/ml corresponded with poor H(2)O(2)-production. L. iners was present at log 10 cells/ml in grade Ib, II and III VMF. Sialidase negative G. vaginalis strains (average log5 cells/ml) were detected in grade I, I-like and IV VMF. In grade II VMF, predominantly a mixture of both sialidase negative and positive G. vaginalis strains (average log9 cells/ml) were present, and predominantly sialidase positive strains in grade III VMF. The presence of A. vaginae (average log9 cells/ml) coincided with grade II and III VMF. P. bivia (log4-8 cells/ml) was mostly present in grade III vaginal microflora. L. iners, G. vaginalis, A. vaginae and P. bivia all increased around menses for group N women, and as such L. iners was considered a member of disturbed VMF.

CONCLUSIONS

This qPCR-based study confirms largely the results of previous culture-based, microscopy-based and pyrosequencing-based studies.

Behavioral predictors of colonization with Lactobacillus crispatus or Lactobacillus jensenii after treatment for bacterial vaginosis: a cohort study

Objective: Evaluate predictors of vaginal colonization with lactobacilli after treatment for bacterial vaginosis (BV). Methods. Vaginal fluid specimens from women with BV underwent qPCR for Lactobacillus crispatus, L. jensenii, and L. iners pre- and posttreatment. Results. Few women with BV were colonized with L. crispatus (4/44, 9%) or L. jensenii (1/44, 2%), though all had L. iners. One month posttreatment 12/44 (27%) had L. crispatus, 12/44 (27%) L. jensenii, and 43/44 (98%) L. iners. Presence of L. jensenii posttreatment was associated with cure (Risk Ratio (RR) 1.67; 95% CI 1.09–2.56); L. crispatus showed a similar trend (RR 1.41; 95% CI 0.89–2.24, P = 0.14). Receptive oral sex was associated with 2.2-log₁₀ lower concentration of L. crispatus (95% CI −4.38, −.02), and digital-vaginal sex with 2.6-log₁₀ lower concentration (95% CI −4.87, −.33). Conclusion. One month after BV treatment, few women established colonization with L. crispatus or L. jensenii. Few behaviors were associated with colonization.

Non-heme manganese catalase--the 'other' catalase

Non-heme manganese catalases are widely distributed over microbial life and represent an environmentally important alternative to heme-containing catalases in antioxidant defense. Manganese catalases contain a binuclear manganese complex as their catalytic active site rather than a heme, and cycle between Mn(2)(II,II) and Mn(2)(III,III) states during turnover. X-ray crystallography has revealed the key structural elements of the binuclear manganese active site complex that can serve as the starting point for computational studies on the protein. Four manganese catalase enzymes have been isolated and characterized, and the enzyme appears to have a broad phylogenetic distribution including both bacteria and archae. More than 100 manganese catalase genes have been annotated in genomic databases, although the assignment of many of these putative manganese catalases needs to be experimentally verified. Iron limitation, exposure to low levels of peroxide stress, thermostability and cyanide resistance may provide the biological and environmental context for the occurrence of manganese catalases.

Lactobacilli at the front line of defense against vaginally acquired infections

Probiotics are microorganisms that provide a health benefit to the host and are promoted as alternatives for the treatment and prevention of infectious diseases and other conditions. One of the most rapidly developing areas of probiotic research is in the management of vaginally acquired infections. Several Lactobacillus species produce compounds that kill or inhibit the growth of vaginally acquired pathogens. Other lactobacilli reduce the adherence of pathogens to urogenital epithelial cells in culture. This article discusses the mechanisms by which vaginal lactobacilli prevent pathogen colonization of the urogenital tract, and potential mechanisms that warrant investigation. Animal models and clinical studies, while limited, are discussed with the idea that these are the next critical steps to advance the study of probiotics for the treatment and prevention of vaginally acquired infections.

Are pathogenic bacteria just looking for food? Metabolism and microbial pathogenesis

It is interesting to speculate that the evolutionary drive for microbes to develop pathogenic characteristics was to access the nutrient resources that animals provided. Animal environments that pathogens colonize have likely driven the evolution of new bacterial characteristics to maximize these new nutritional opportunities. This review focuses on genomic and functional aspects of pathogen metabolism that allow efficient utilization of nutrient resources provided by animals. Similar to genes encoding specific virulence traits, genes encoding metabolic functions have been horizontally acquired by pathogens to provide a selective advantage in host tissues. Selective advantage in host tissues can also be gained by loss of function mutations that alter metabolic capabilities. Greater understanding of bacterial metabolism within host tissues should be important for increased understanding of host-pathogen interactions and the development of future therapeutic strategies.

Microbial biofilms on the surface of intravaginal rings worn in non-human primates

Millions of intravaginal rings (IVRs) are used by women worldwide for contraception and for the treatment of vaginal atrophy. These devices also are suitable for local and systemic sustained release drug delivery, notably for antiviral agents in human immunodeficiency virus pre-exposure prophylaxis. Despite the widespread use of IVRs, no studies have examined whether surface-attached bacterial biofilms develop in vivo, an important consideration when determining the safety of these devices. The present study used scanning electron microscopy, fluorescence in situ hybridization and confocal laser scanning microscopy to study biofilms that formed on the surface of IVRs worn for 28 days by six female pig-tailed macaques, an excellent model organism for the human vaginal microbiome. Four of the IVRs released the nucleotide analogue reverse transcriptase inhibitor tenofovir at a controlled rate and the remaining two were unmedicated. Large areas of the ring surfaces were covered with monolayers of epithelial cells. Two bacterial biofilm phenotypes were found to develop on these monolayers and both had a broad diversity of bacterial cells closely associated with the extracellular material. Phenotype I, the more common of the two, consisted of tightly packed bacterial mats approximately 5 µm in thickness. Phenotype II was much thicker, typically 40 µm, and had an open architecture containing interwoven networks of uniform fibres. There was no significant difference in biofilm thickness and appearance between medicated and unmedicated IVRs. These preliminary results suggest that bacterial biofilms could be common on intravaginal devices worn for extended periods of time.

Microbiota restoration: natural and supplemented recovery of human microbial communities

In a healthy host, a balance exists between members of the microbiota, such that potential pathogenic and non-pathogenic organisms can be found in apparent harmony. During infection, this balance can become disturbed, leading to often dramatic changes in the composition of the microbiota. For most bacterial infections, nonspecific antibiotics are used, killing the non-pathogenic members of the microbiota as well as the pathogens and leading to a substantial delay in the restoration of a healthy microbiota. However, in some cases, infections can self-resolve without the intervention of antibiotics. In this Review, we explore the mechanisms underlying microbiota restoration following insult (antibiotic or otherwise) to the skin, oral cavity, and gastrointestinal and urogenital tracts, highlighting recovery by natural processes and after probiotic administration.