By Davina-Nelson Apiyo

The vaginal microbiota is a complex and dynamic ecosystem. This polymicrobial community constitutes beneficial Lactobacilli, as well as commensal anaerobes, including species from the genera Gardnerella, Atopobium, Mobiluncus and Prevotella (Smith & Ravel, 2017). Lactobacilli serve as the primary colonizing bacteria within the female genital tract (FGT) of a healthy woman; their antagonistic properties – production of lactic acid and bacteriocins – keep the vaginal environment acidic, thereby inhibiting the growth of potentially pathogenic commensal anaerobes. However, various internal and external manipulative stimuli (such as menstruation, sexual activity, douching, hormonal influences and antibiotherapy) (Amabebe & Anumba, 2018) can bring about changes to the microbiome, resulting in a decline in Lactobacilli numbers and a concomitant increase in anaerobe numbers. This excessive proliferation of commensal anaerobes is associated with the manifestation of bacterial vaginosis (BV), a bacterial infection that mostly affects women of reproductive age.

This genital condition was once considered a nuisance infection, but further studies on this microbial dysbiosis revealed that its presence in the FGT leads to an increased risk in reproductive and obstetric-related complications – such as preterm delivery and pelvic inflammatory disease – as well as a higher risk of acquisition of sexually transmitted infections. Epidemiological studies also show that women of African ethnicity are at a higher risk of acquiring the disease, as well as female subjects with intermediate (reduced Lactobacilli) vaginal flora (Cherpes et al., 2008). Its aetiology remains unclear, though Gardnerella vaginalis has historically been thought to be the main cause of this condition (Gardner & Dukes, 1955).

Currently, the recommended standard of care is antibiotic therapy, either through the oral or intravaginal use of metronidazole or clindamycin. Yet, this form of therapy has been deemed inadequate, given the high rates of recurrence of the infection three to six months post-treatment (Bradshaw et al., 2006). This issue has necessitated investigation of alternative forms of therapy that can reduce the recurrence of BV, one of which is the use of probiotics. A number of clinical trials have been undertaken to demonstrate the efficacy of certain probiotic strains in alleviating BV symptoms, many of which have shown promising results (Anukam et al., 2006; Marcone et al., 2008; Martinez et al., 2009; Rossi et al., 2010; Vujic et al., 2013). Nonetheless, there is still some hesitancy in using probiotics as a standalone treatment or adjuvant therapy to antibiotics, because of the heterogeneity of the BV cure rates. The difference in results is brought about by the varying methodologies (in terms of sample sizes, study designs, diagnosis criteria, treatment regimens and probiotic stains) that these clinical trials employ. How can we find the most promising candidates before testing them in clinical cohorts? It would be of benefit, to have a standard protocol by which probiotic efficacy can be tested prior to clinical trials. This is where we come in; as a collaborative effort from researchers at the Centre for Bioprocess Engineering (CeBER) at the University of Cape Town and the Bioelectronic Systems Technology (BEST) labs at the University of Cambridge, we propose developing a standardized in vitro model for testing potential biotherapeutics for BV treatment. This model is to be developed under conditions that closely mimic the in vivo environment of the FGT.

The proposed model will comprise vaginal epithelial cells (ECs) cultured in a three-dimensional manner, by seeding these cells into a scaffold. This cell culturing format will ascertain the development of multicellular structures that closely resemble in vivo vaginal ECs. The scaffold in question not only serves as a structure for cellular growth and differentiation, but also permits the non-invasive monitoring of cells through electrical impedance spectroscopy. This is made possible due to its conductive nature – the material of the scaffold is composed of a conjugated polymer film that can be used to measure the transepithelial electrical resistance of a polarized epithelium (Jimison et al., 2012; Moysidou et al., 2021; Tria et al., 2014). This measurement aids in exploring the integrity of the in vitro vaginal tissue. We hypothesize that biofilm formation by G. vaginalis on the vaginal epithelial layer can be used as a physiological marker of BV (Patterson et al., 2010; Swidsinski et al., 2005), as well as a tracking feature for the measure of BV treatment. Therefore, upon setting up the model, the vaginal ECs will be colonised with G. vaginalis (to manifest the condition), after which probiotic Lactobacilli will be added, to investigate its ability to break down the biofilm, and in turn, deter G. vaginalis growth.

Inasmuch as the project scope does not seek to determine the actual aetiological agent of BV, it is envisioned that the establishment of this model could serve as a baseline for such work. Furthermore, this system has the potential to be a standard pre-clinical model that can be used to not only test for probiotic efficacy and safety, but also eliminate potential strains that would have a poor efficacy in a clinical trial setting. In the long run, we seek to develop a region-specific probiotic that reduces BV recurrence in South African women.

Davina-Nelson Apiyo (apydav001@myuct.ac.za) is a doctoral student at the Centre for Bioprocess Engineering (CeBER) at the University of Cape Town, South Africa.

She is under the supervision of Dr. Marijke Fagan-Endres (marijke.fagan-endres@uct.ac.za). Development of the 3D model is in collaboration with Prof Rόisίn M. Owens (University of Cambridge).

References

Amabebe, E., & Anumba, D. O. C. (2018). The vaginal microenvironment: The physiologic role of Lactobacilli. Frontiers in Medicine, 5(JUN), 1–11. https://doi.org/10.3389/fmed.2018.00181

Anukam, K. C., Osazuwa, E., Osemene, G. I., Ehigiagbe, F., Bruce, A. W., & Reid, G. (2006). Clinical study comparing probiotic Lactobacillus GR-1 and RC-14 with metronidazole vaginal gel to treat symptomatic bacterial vaginosis. Microbes and Infection, 8(12–13), 2772–2776. https://doi.org/10.1016/j.micinf.2006.08.008

Bradshaw, C. S., Morton, A. N., Hocking, J., Garland, S. M., Morris, M. B., Moss, L. M., Horvath, L. B., Kuzevska, I., & Fairley, C. K. (2006). High recurrence rates of bacterial vaginosis over the course of 12 months after oral metronidazole therapy and factors associated with recurrence. Journal of Infectious Diseases, 193(11), 1478–1486. https://doi.org/10.1086/503780

Cherpes, T. L., Hillier, S. L., Meyn, L. A., Busch, J. L., & Krohn, M. A. (2008). A delicate balance: Risk factors for acquisition of bacterial vaginosis include sexual activity, absence of hydrogen peroxide-producing lactobacilli, black race, and positive herpes simplex virus type 2 serology. Sexually Transmitted Diseases, 35(1), 78–83. https://doi.org/10.1097/OLQ.0b013e318156a5d0

Gardner, H. L., & Dukes, C. D. (1955). Haemophilus vaginalis vaginitis: A newly defined specific infection previously classified “nonspecific” vaginitis. American Journal of Obstetrics and Gynecology, 69(5), 962–976.

Jimison, L. H., Tria, S. A., Khodagholy, D., Gurfinkel, M., Lanzarini, E., Hama, A., Malliaras, G. G., & Owens, R. M. (2012). Measurement of barrier tissue integrity with an organic electrochemical transistor. Advanced Materials, 24(44), 5919–5923. https://doi.org/10.1002/adma.201202612

Developing a standardized model for testing novel probiotics for the treatment of bacterial vaginosis in South African women.