Peptidomimetic cationic amphiphiles for the control of biofilms and antibiotic resistance in bacterial vaginosis
Creators: name: Weeks, Richard
Publisher: name: No Publisher Supplied
Year: 2021

description: Bacterial vaginosis (BV) is a polymicrobial bacterial infection and the most common vaginal disorder in women of reproductive age. BV is characterized by dysbiosis and a shift in the vaginal microbiota from a Lactobacillus-dominated environment to one with an increased prevalence of opportunistic anaerobic pathogens, including Gardnerella vaginalis, Prevotella bivia, Peptostreptococcus anaerobius, and Mobiluncus curtisii. The exact cause for this shift is not well understood, and no single etiological agent can be identified. However, the anaerobic and Gram-variable pathogen Gardnerella vaginalis is isolated in some 98% of BV cases and is considered by many to be a keystone species in bacterial vaginosis. Together, the BV-associated species form a robust polymicrobial biofilm. Cells within the biofilm exhibit synergy and are highly resistant to the action of antibiotics, resulting in a high risk of antibiotic resistance development and treatment failure. The reoccurrence rate following antibiotic treatment is as high as 78% within the first 6 months, which is often associated with antibiotic-resistant pathogens. Therefore, effective strategies must be developed in the search for antibiotic alternatives for the treatment of BV.The dissertation-related published reports include three major components of the study. The first chapter reviews naturally occurring antimicrobial peptides, their key physicochemical properties, and how those properties interact and influence the pharmacology of peptide-based antimicrobials. Key limitations that have prevented their widespread use against human pathogens related to these intrinsic properties are also discussed. These factors are then discussed in the context of peptidomimetic drug design, providing an overview of several different approaches for improving and developing novel peptides and peptidomimetics via chemical modification and other strategic alterations. Together, this chapter serves as a framework for the development of rationally designed and selective antimicrobial peptides and peptidomimetics that are effective against antibiotic resistant pathogens while also lowering the risk of antibiotic resistance development in the first place.The second chapter is focused on a novel series of synthetic peptidomimetic antimicrobial compounds, know as cationic amphiphiles (CAms) and their activity against bacterial vaginosis pathogens, their biofilms, and representative species of the vaginal commensal microbiota. This study also investigated potential synergy between the peptidomimetic compounds and the nitroimidazole antibiotic metronidazole. The CAms were effective against planktonic cells of all tested pathogens and in inhibiting biofilm formation and killing preformed biofilms of G. vaginalis at clinically relevant concentrations. The action of the CAms against G. vaginalis biofilms, both alone and in combination with metronidazole, was confirmed by SEM imaging. Notably, the tested healthy vaginal lactobacilli were found to be significantly more resistant to the CAms, which was not unexpected according to the design of the studied CAms. The CAms also showed pote synergy in combination with metronidazole, which may significantly reduce the risk of antibiotic resistance development in bacterial vaginosis pathogens.The third chapter is focused on a second generation of rationally designed peptidomimetic antimicrobials, designed based on the reported antimicrobial activity of the earlier series of compounds, and investigates their activity against bacterial vaginosis pathogens, G. vaginalis and Lactobacillus biofilms, and representative species of the vaginal commensal microbiota. This study also includes the generation of bacterial strains resistant to either metronidazole or clindamycin, their genetic characterization, and an investigation of the peptidomimetic antimicrobials activity against these strains. Interestingly, the CAm compounds were found to be as effective or more effective against the generated resistant strains than wild-type G. vaginalis. Synergy together with metronidazole and clindamycin was also assessed using a checkerboard assay and the calculation of fractional inhibitory concentrations, showing a potential additive effect for the majority of the tested CAm compounds. The potential safety of the CAm compounds was investigated for mutagenic potential using a modified Ames test and for toxicity against using the epivaginal ectocervical tissue model developed by MatTek. Notably, no mutagenic potential or toxicity were detected for the tested CAm compounds at inhibitory and biofilm killing concentrations.Together, these studies represent the culmination of a comprehensive, multidisciplinary effort towards the development, characterization, and implementation of small molecule peptidomimetic antimicrobials to control pathogenic biofilms and antibiotic resistance development with minimal toxicity and activity against the commensal microbiota and host tissues.