Starvation Survival and Biofilm Formation under Subminimum Inhibitory Concentration of QAMs.

Sanjay Kumar Tiwari,Biao Ren,Yannan Huang,Mingyun Li,Xuedong Zhou,Lei Cheng,Xian Peng,Hockin H K Xu,Yan Xiao,Suping Wang,Luca Fiorillo

doi:10.1155/2021/8461245

Abstract

Quaternary ammonium methacrylates (QAMs) are useful antimicrobial compounds against oral bacteria. Here, we investigated the effects of two QAMs, dimethylaminododecyl methacrylate (DMADDM) and dimethylaminohexadecyl methacrylate (DMAHDM), on biofilm formation, survival and development of tolerance by biofilm, and survival and development of tolerance against QAMs after prolonged starvation. Enterococcus faecalis (E. faecalis), Streptococcus gordonii (S. gordonii), Lactobacillus acidophilus (L. acidophilus), and Actinomyces naeslundii (A. naeslundii) were used. Minimum inhibitory concentration (MIC) of QAMs against multispecies biofilm was determined. Biofilm formed under sub-MIC was observed by crystal violet staining and confocal laser scanning microscopy (CLSM). Metabolic activity was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and lactic acid production measurement. Development of tolerance was determined by MIC values before and after exposure to QAMs or after prolonged starvation. It was found that E. faecalis and S. gordonii could survive and form biofilm under sub-MIC of QAMs. Lactic acid production from biofilms formed under sub-MIC was significantly higher than control specimens (p < 0.05). The exposure to sub-MIC of QAMs promoted biofilm formation, and prolonged starvation or prolonged contact with sub-MIC helped bacteria develop tolerance against killing by QAMs.

Highlights

Dental diseases, including persistent periapical infection, are biofilm-mediated infections, which have been associated with the etiology of several systemic diseases, ranging from arthritis to neurodegenerative diseases [1,2,3,4]
The number of E. faecalis, S. gordonii, and L. acidophilus was significantly increased on day 15 (p < 0:05)
The proportion of S. gordonii increased on day 20 before observation, and the growth trend continued until day 25, after which it began to decline

Summary

Introduction

Dental diseases, including persistent periapical infection, are biofilm-mediated infections, which have been associated with the etiology of several systemic diseases, ranging from arthritis to neurodegenerative diseases [1,2,3,4]. Enterococcus spp., Lactobacillus spp., Streptococcus spp., and Actinomyces spp. are the most common species in persistent periapical infection [6, 7]. These bacteria can be well entrenched in the root canal system under lethal concentrations of root canal irrigants and starvation due to biofilm formation and synergistic effects. The use of antimicrobial compounds or antibiotics is an effective way to control bacterial infection in the root canal system [8,9,10,11,12,13,14,15,16].

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