In vitro Antibacterial Activity of an FDA-Approved H+-ATPase Inhibitor, Bedaquiline, Against Streptococcus mutans in Acidic Milieus

Abstract

BackgroundDental caries is an acid-related disease. Current anti-caries agents mainly focus on the bacteriostatic effect in a neutral environment and do not target acid-resistant microorganisms related to caries in acidic milieus.ObjectivesTo assess the in vitro antibacterial activities of bedaquiline against oral pathogens in acidic milieus.MethodsStreptococcus mutans, Streptococcus sanguinis, and Streptococcus salivarius were used to prepare the mono-/multiple suspension and biofilm. The MIC and IC50 of bedaquiline against S. mutans were determined by the broth microdilution method. Bedaquiline was compared regarding (i) the inhibitory activity in pH 4–7 and at different time points against planktonic and biofilm; (ii) the effect on the production of lactic acid, extracellular polysaccharide, and pH of S. mutans biofilm; (iii) the cytotoxicity effects; and (iv) the activity on H+-ATPase enzyme of S. mutans.ResultsIn pH 5 BHI, 2.5 mg/L (IC50) and 4 mg/L (MIC) of bedaquiline inhibited the proliferation and biofilm generation of S. mutans and Mix in a dose-dependent and time-dependent manner, but it was invalid in a neutral environment. The lactic acid production, polysaccharide production, and pH drop range reduced with the incorporation of bedaquiline in a pH 5 environment. Its inhibitory effect (>56 mg/L) against H+-ATPase enzyme in S. mutans and its non-toxic effect (<10 mg/L) on periodontal ligament stem cells were also confirmed.ConclusionBedaquiline is efficient in inhibiting the proliferation and biofilm generation of S. mutans and other oral pathogens in an acidic environment. Its high targeting property and non-cytotoxicity also promote its clinical application potential in preventing caries. Further investigation of its specific action sites and drug modification are warranted.

A New pH-Responsive Nano Micelle for Enhancing the Effect of a Hydrophobic Bactericidal Agent on Mature Streptococcus mutans Biofilm

“…25 μg ml –1 bedaquiline) reduced the growth rate of the bacteria to half that of the control ( p < 0.001). Our pervious study had found that at pH 7, bedaquiline cannot inhibit the biofilm formation of S. mutans ( Zhang et al, 2021 ). In order to figure out the reasons for these inconsistent results, we had conducted additional study to measure the pH change of medium during bacterial growth.…”

“…The stable and cohesive biofilm formed by S. mutans ( Cross et al, 2006 ; Koo et al, 2013 ) can block the penetration of antibacterial agents, including bedaquiline ( Zhang et al, 2021 ). This is a key self-protection property of biofilms.…”

“…Dental biofilm mainly relies on exopolysaccharides to strengthen the interconnection between bacterial cells ( Koo et al, 2013 ; Lin et al, 2021 ). Bedaquiline has no influence on the carbohydrate metabolism of S. mutans , while it can bind to H + -ATPase and destroy the cell membrane, exerting a bactericidal effect ( Zhang et al, 2021 ). The bactericide effect on mature biofilm found in the present study shows that the study nanomicelle drug delivery system facilitates the penetration of bedaquiline into bacterial biofilm, making the contact between bedaquiline and bacteria available, and then killing the bacteria inside the biofilm.…”

“…This microecology not only provides a great haven for the reproduction of caries pathogens and the fermentation of an acidic environment ( Filoche et al, 2010 ) but also resists attack from foreign substances, including antibiotics and antibacterial agents ( Pizzolato-Cezar et al, 2019 ). Many agents have an antibacterial effect on cariogenic pathogens in suspension ( Jiang et al, 2020 ; Zhang et al, 2021 ), but it is extremely difficult for these agents to penetrate into biofilm and attack the pathogens in the biofilm. This is a major challenge for the clinical applications of these agents for dental caries management.…”

“…Bedaquiline is an inhibitor that targets an acid-resistant protein H + -ATPase ( Preiss et al, 2015 ). Results of our previous study show that bedaquiline can potently inhibit the growth of Streptococcus mutans ( S. mutans ) suspension and biofilm generation in acidic environment (pH 5) but has no effect in neutral environment ( Zhang et al, 2021 ). Besides, this hydrophobic agent cannot exert bactericidal effect on the bacteria within biofilm.…”