Characterisation of biofilm associated with bacterial vaginosis

    Research output: ThesisDoctoral dissertation - Doctoral dissertation

    Abstract

    The vagina plays a major part in the likelihood of conception and the probability of a full term delivery, and in the protection against intruding pathogens. The state of the vaginal environment is very important for a positive outcome. The most favourable state of the vaginal microbiome is one in which the lactobacilli are abundant, and in which the vagina is protected and kept moist by cervicovaginal fluid. Conversely, a considerably unfavourable microbiome state is one where the beneficial lactobacilli are being overruled by other, more pathogenic, anaerobic bacteria, as seen in bacterial vaginosis (BV).
    BV is the most prevalent vaginal disorder worldwide, and is associated with an entire array of serious gynaecological and obstetric complications and with an increased incidence of sexually transmitted infections (STIs). At present, little knowledge about the exact aetiology of BV is available, but the typical spectrum of bacteria that overgrow the vaginal microbiome in BV has been reasonably well-described. The two main players in this vaginal microbiome imbalance are Gardnerella vaginalis, often found in the Lactobacillus-dominated microbiome as well, and Atopobium vaginae. In addition, the presence of a bacterial biofilm in BV has been established to a certain extent, and is reflected by the presence of clue cells, epithelial cells covered with bacteria, in the vaginal fluid. This bacterial biofilm is a polymicrobial group of sessile bacteria adhering to the vaginal epithelium sticking together in a self-produced mucous matrix. Being part of a biofilm results in an enhanced tolerance to antimicrobial treatment and to the host immune system.
    In this thesis, we delved into the role of G. vaginalis and A. vaginae in the BV biofilm. We designed new probes for fluorescence in situ hybridisation (FISH) to visualise and identify G. vaginalis and A. vaginae in the biofilm using vaginal samples on microscopy slides. Using FISH, we were able to confirm and visualise the dominant presence of G. vaginalis in the biofilm. Further, we reported on the symbiosis between A. vaginae and G. vaginalis: the probability of having BV increased when A. vaginae was present in the G. vaginalis-dominated biofilm.
    Because G. vaginalis can also be detected in the health-associated lactobacilli-dominated microbiome, we explored the role of G. vaginalis’ sialidase gene. Sialidase is an enzyme that can increase the virulence of G. vaginalis, for example by facilitating adherence to the epithelium after cleaving of the sialic acid on the glycans of mucous epithelial membranes. We established that the presence of the G. vaginalis sialidase gene, as measured by quantitative polymerase chain reaction (qPCR) in the vaginal specimens, was associated with a BV diagnosis and with the existence of a G. vaginalis-dominated biofilm. The impact of the polymicrobial biofilm and the ability of G. vaginalis to produce sialidase are important findings which could lead to improved techniques for BV diagnosis. Furthermore, these results should be taken into account while designing and developing new strategies for BV treatment and prevention.
    The existence of a vaginal biofilm is of importance in relation to medical devices applied vaginally such as vaginal rings. Currently, vaginal rings are available for contraception and treatment of vaginal atrophy. Moreover, rings are also being developed and studied for the controlled release of compounds to prevent and treat STIs. Limited information is available on the colonisation of these vaginal rings when used continuously for a period of three months or more. We demonstrated that it was common for vaginal rings to be covered with biomass consisting of vaginal epithelial cells and associated bacteria after three weeks use. We also showed that a higher density of this biomass on the contraceptive rings was related to: BV, a vaginal biofilm with G. vaginalis and A. vaginae, and the presence of A. vaginae on the contraceptive vaginal ring. More research will be needed to better understand if this biomass could have an impact on the vaginal microbiome state and, possibly, on the release of active product from the rings.
    The work leading to this thesis has contributed to solving part of the complicated BV puzzle, but –as always– more research will be needed to determine the role of BV-associated bacteria to unravel the aetiology of BV.
    Original languageEnglish
    Publication statusPublished - 2016

    Keywords

    • B780-tropical-medicine

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