AUTHOR=Liu Xiaoju , Xiong Yanpeng , Shi Yiyi , Deng Xiangbin , Deng Qiwen , Liu Yansong , Yu Zhijian , Li Duoyun , Zheng Jinxin , Li Peiyu 

TITLE=In vitro activities of licochalcone A against planktonic cells and biofilm of Enterococcus faecalis

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.970901

DOI=10.3389/fmicb.2022.970901

ISSN=1664-302X

ABSTRACT=<p>This study aims to evaluate the <italic>in vitro</italic> antibacterial and anti-biofilm activities of licochalcone A on <italic>Enterococcus faecalis</italic> and to investigate the possible target genes of licochalcone A in <italic>E. faecalis</italic>. This study found that licochalcone A had antibacterial activities against <italic>E. faecalis</italic>, with the MIC<sub>50</sub> and MIC<sub>90</sub> were 25 μM. Licochalcone A (at 4 × MIC) indicated a rapid bactericidal effect on <italic>E. faecalis</italic> planktonic cells, and killed more <italic>E. faecalis</italic> planktonic cells (at least 3-log<sub>10</sub> cfu/ml) than vancomycin, linezolid, or ampicillin at the 2, 4, and 6 h of the time-killing test. Licochalcone A (at 10 × MIC) significantly reduced the production of <italic>E. faecalis</italic> persister cells (at least 2-log<sub>10</sub> cfu/ml) than vancomycin, linezolid, or ampicillin at the 24, 48, 72, and 96 h of the time-killing test. Licochalcone A (at 1/4 × MIC) significantly inhibited the biofilm formation of <italic>E. faecalis</italic>. The RNA levels of biofilm formation-related genes, <italic>agg, esp</italic>, and <italic>srtA</italic>, markedly decreased when the <italic>E. faecalis</italic> isolates were treated with licochalcone A at 1/4 × MIC for 6 h. To explore the possible target genes of licochalcone A in <italic>E. faecalis</italic>, the licochalcone A non-sensitive <italic>E. faecalis</italic> clones were selected <italic>in vitro</italic> by induction of wildtype strains for about 140 days under the pressure of licochalcone A, and mutations in the possible target genes were detected by whole-genome sequencing. This study found that there were 11 nucleotide mutations leading to nonsynonymous mutations of 8 amino acids, and among these amino acid mutations, there were 3 mutations located in transcriptional regulator genes (MarR family transcriptional regulator, TetR family transcriptional regulator, and MerR family transcriptional regulator). In conclusion, this study found that licochalcone A had an antibacterial effect on <italic>E. faecalis</italic>, and significantly inhibited the biofilm formation of <italic>E. faecalis</italic> at subinhibitory concentrations.</p>