# Antibacterial Effects of _Paeonia lactiflora_ Extract on Oral Microcosm Biofilms
###### Abstract  
The aim of this study was to evaluate the antibacterial effects of _Paeonia lactiflora_ (PL) extract on oral microcosm biofilms and determine its usefulness as a natural alternative to current antimicrobial agents. Oral biofilms were cultivated on hydroxyapatite disks using human saliva for 2 days, following which they were treated with 1.5 mL of distilled water (DW), 30 \(\mathrm{\SIUnitSymbolMicro g}\)/mL of PL extract, or 0.12% chlororexidine gluconate (CHX) once daily for 3 days. Antibacterial effects were assessed by measuring red fluorescence intensity (Ratio\({}_{\mathrm{f/G}}\)), bacterial viability (Ratio\({}_{\mathrm{G/G+R}}\)), and aciduric bacterial counts. Ratio\({}_{\mathrm{f/G}}\) was evaluated using quantitative light-induced fluorescence digital imaging. Ratio\({}_{\mathrm{f/G}}\) and Ratio\({}_{\mathrm{C/G+R}}\) in the PL group were 0.94-fold and 0.73-fold lower than those in the DW group (\(p<0.001\) and \(p=0.011\), respectively) and comparable to those in the CHX group (\(p=0.356\) and \(p=0.964\), respectively). Aciduric bacterial counts in the PL group were 0.97-fold lower than those in the DW group (\(p<0.001\)), with no significant difference from those in the CHX group (\(p=0.892\)). Thus, the antibacterial effect of PL extract was comparable to that of CHX; this suggests its potential as a natural alternative for managing oral biofilm-associated diseases. oral microcosm biofilm; _Paeonia lactiflora_ extract; natural antimicrobial agents; antibacterial effects; saliva +
Footnote †: journal: Applied sciences  
Mechanical removal using methods such as toothbrushing is the most important strategy for managing oral biofilms on teeth. However, mechanical removal alone may not be sufficient to manage mature oral biofilms, particularly in hard-to-reach areas of the oral cavity. Therefore, antimicrobial agents are often used as complementary strategies [13]. However, as oral biofilms mature, their resistance to external antimicrobial agents increases. This can be attributed to the physical barrier formed by the oral biofilm, which hinders the penetration of external substances [14]. The antimicrobial efficacy of 0.2% chlororexidine (CHX) has been shown to be limited to the outermost layer of the oral biofilm, with minimal effects in deeper layers [15]. Furthermore, chemical antimicrobial agents such as CHX can cause an accumulation of dead bacteria within the oral biofilm, potentially providing new attachment sites for live bacteria and consequently promoting recolonization [16; 17]. Thus, it is necessary to identify novel antimicrobial agents that can overcome the limitations of conventional treatments and inhibit the growth of pathogenic oral bacteria. Natural substances have been used for the treatment of diseases for centuries, and their antimicrobial properties are well documented [18]. Previous studies have demonstrated the antimicrobial effects of natural substances against oral microorganisms, particularly their ability to inhibit the synthesis of EPSs [19; 20; 21; 22]. Among these, _Paeonia laciflora_ (PL), commonly known as Chinese peony, is a well-known antimicrobial herbal medicine, with its antimicrobial effects reported in various studies [23; 24; 25; 26]. One of the primary active components of PL, paeoniflorin, is a monoterpene glycoside that exhibits antioxidant, anti-inflammatory, and anticonvulsant effects [27], and it is a known therapeutic component used in the treatment of anemia, menstrual disorders, and rheumatoid arthritis [28]. Notably, a previous study reported that PL extract has antimicrobial effects against the oral pathogens _S. mutans_ and _Candida albicans_[29]. Most studies have employed single-species oral biofilm models; however, in reality, more than 1000 different bacterial species have been collectively identified across individuals, with each individual hosting a subset of these diverse species [30]. These bacterial species exhibit complex interactions that contribute to the structural stability and antimicrobial resistance of oral biofilms [31].