Abstract
The common but poorly understood condition known as bacterial vaginosis (BV) increases vulnerability to HIV infection and is associated with the absence of H2O2-producing Lactobacillus. Vaginal lactic acid bacteria (LAB) produce anti-HIV factors such as organic acids and hydrogen peroxide (H2O2), and may bind and inactivate HIV particles during scavenging of mannose. These factors define potential criteria for initial selection of candidate probiotics to block heterosexual transmission of HIV. Therefore, the primary goal of this study was to characterize acid production on mannose and H2O2 production in vaginal isolates from Canadian adolescents (192 isolates, 16 individuals) and commercial sex workers in Nairobi, Kenya (576 isolates, 96 individuals). Selection of isolates from H2O2-detecting media suggested an idiosyncratic individual-level profile and extensive phenotypic diversity, including the identification of a subset of “double-strong” acid- and H2O2-producers with phenotypes similar to well-characterized probiotic strains. Molecular fingerprinting of all isolates by capillary electrophoresis of 16S-23S rRNA interspacer amplicons was coupled with chaperonin-60 universal target (cpn60 UT) sequencing in a subset, tentatively identifying 96% of isolates although only 19% were sequenced. Most isolates belonged to Lactobacillus, Streptococcus, Bifidobacterium or Gardnerella, with a total of 37 species in 15 genera, as well as 5 potentially novel organisms, identified in this study. This sensitivity was likely enhanced by phenotype-based selection on two chromogenic media formulations. Identification of double-strong isolates may provide a rational basis for selection and further characterization of vaginal probiotics, with potential application as part of HIV prevention initiatives in western Canada and East Africa.
Highlights
Colonization of the female genital tract by Lactobacillus species is recognized as critical for overall vaginal health and resistance to infection by bacterial and viral pathogens, including HIV [1,2,3]
Since the specific application we propose for these organisms is as vaginal probiotics for prevention of HIV infection, we propose that identifying and artificially increasing the levels of known mannose-scavenging, HIV-inactiviting probiotics in a population may represent a novel approach to HIV prevention in high-risk groups
Phenotyping experiments were optimized using a panel of relevant bacterial strains and tested for acid and H2O2 production using chromogenic media
Summary
Colonization of the female genital tract by Lactobacillus species is recognized as critical for overall vaginal health and resistance to infection by bacterial and viral pathogens, including HIV [1,2,3]. Linked with negative reproductive health outcomes, such as miscarriage, premature birth, post-operative infections, pelvic inflammatory disease and HIV infection, its etiology and clinical course remain poorly defined with a consequent lack of effective prevention and treatment strategies [5,6,7]. Especially by Lactobacillus species, reduces the overall pH of the vaginal lumen to ‘‘normal’’ levels, in the range of 3.9 to 4.5 [9,10]. Along with effectors such as H2O2 and bacteriocins, acid production by Lactobacillus is believed to discourage overgrowth of other bacterial genera including Streptococcus, Gardnerella, Bacteroides and Mycoplasma [11]. Production of acid and H2O2 may be synergistic, since bacterial H2O2 is more likely to remain stable at lower pH in vitro [13]
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