Abstract
Only two reports exist on drug-resistance of quaternary ammonium monomers against oral bacteria; both studies tested planktonic bacteria for 10 passages, and neither study tested biofilms or resins. The objectives of this study were to investigate the drug-resistance of Streptococcus mutans, Streptococcus sanguinis and Streptococcus gordonii against dimethylaminohexadecyl methacrylate (DMAHDM), and to evaluate biofilms on resins with repeated exposures for 20 passages for the first time. DMAHDM, dimethylaminododecyl methacrylate (DMADDM) and chlorhexidine (CHX) were tested with planktonic bacteria. Biofilms were grown on a resin containing 3% DMAHDM. Minimum-inhibitory concentrations were measured. To detect drug-resistance, the survived bacteria from the previous passage were used as inoculum for the next passage for repeated exposures. S. gordonii developed drug-resistance against DMADDM and CHX, but not against DMAHDM. Biofilm colony-forming units (CFU) on DMAHDM-resin was reduced by 3–4 log; there was no difference from passages 1 to 20 (p > 0.1). No drug-resistance to DMAHDM was detected for all three bacterial species. In conclusion, this study showed that DMAHDM induced no drug-resistance, and DMAHDM-resin reduced biofilm CFU by 3–4 log, with no significant change from 1 to 20 passages. DMAHDM with potent antibacterial activities and no drug-resistance is promising for dental applications.
Highlights
Dental caries is a prevalent biofilm-infectious disease and a major public health problem globally with heavy economic burdens[1]
Antibacterial dental materials containing quaternary ammonium monomers (QAMs) have promising clinical benefits, little attention has been paid to the emergence of potential antibacterial drug resistance in oral microorganism induced by QAMs
The present study investigated three caries-related oral species: S. gordonii, S. sanguinis, and cariogenic S. mutans, which were exposed to dimethylaminohexadecyl methacrylate (DMAHDM) resin for 20 passages, with the results that 3% DMAHDM resin could effectively inhibit most of the bacteria in the biofilm without resistant bacteria accumulation
Summary
Dental caries is a prevalent biofilm-infectious disease and a major public health problem globally with heavy economic burdens[1]. It has been reported that bacteria embedded in a biofilm are up to 1000-fold more resistant to antibiotics compared to their planktonic counterparts[31] In these two studies[29,30], the QAM was dissolved in the culture medium, not co-polymerized in a dental resin as a clinically-relevant restorative material. A literature search revealed no report on: (1) investigation of drug resistance in oral or non-oral biofilms induced by QAMs (previous studies only tested planktonic bacteria); (2) testing of bacterial drug resistance for QAM-containing resins (previous studies only added QAM into culture medium); and (3) evaluation of relatively longer-term drug resistance with repeated exposures to a QAM for more than 10 passages. The objectives of this study were to investigate the drug resistance of oral bacteria against QAM in both planktonic and biofilm forms, with DMAHDM being co-polymerized in a dental resin and having repeated exposures for 20 passages. It was hypothesized that: (1) Different antibacterial agents (DMAHDM, DMADDM, CHX) would induce different levels of drug resistance in planktonic bacteria; (2) Different oral bacterial species would exhibit different drug resistance properties against the same antibacterial agent; (3) The new DMAHDM would not induce drug resistance in planktonic bacteria and biofilms, whether being incorporated into the culture medium or co-polymerized in a dental resin, from passages 1 to 20
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