Transcriptional and Functional Analysis of the Effects of Magnolol: Inhibition of Autolysis and Biofilms in Staphylococcus aureus

Dacheng Wang,Mingxun Xing,Hua Xiang,Xiaohong Wang,Fengge Shen,Qi Jin,Lu Yu,Xuming Deng,Rizeng Meng,Lihui Liu,Na Guo,Haihua Feng,Xudong Tang,Kaiyu Zhang,Wei Wang,Junchao Liang,J Ross Fitzgerald

doi:10.1371/journal.pone.0026833

Abstract

BackgroundThe targeting of Staphylococcus aureus biofilm structures are now gaining interest as an alternative strategy for developing new types of antimicrobial agents. Magnolol (MOL) shows inhibitory activity against S. aureus biofilms and Triton X-100-induced autolysis in vitro, although there are no data regarding the molecular mechanisms of MOL action in bacteria.Methodology/Principal FindingsThe molecular basis of the markedly reduced autolytic phenotype and biofilm inhibition triggered by MOL were explored using transcriptomic analysis, and the transcription of important genes were verified by real-time RT-PCR. The inhibition of autolysis by MOL was evaluated using quantitative bacteriolytic assays and zymographic analysis, and antibiofilm activity assays and confocal laser scanning microscopy were used to elucidate the inhibition of biofilm formation caused by MOL in 20 clinical isolates or standard strains. The reduction in cidA, atl, sle1, and lytN transcript levels following MOL treatment was consistent with the induced expression of their autolytic repressors lrgA, lrgB, arlR, and sarA. MOL generally inhibited or reversed the expression of most of the genes involved in biofilm production. The growth of S. aureus strain ATCC 25923 in the presence of MOL dose-dependently led to decreases in Triton X-100-induced autolysis, extracellular murein hydrolase activity, and the amount of extracellular DNA (eDNA). MOL may impede biofilm formation by reducing the expression of cidA, a murein hydrolase regulator, to inhibit autolysis and eDNA release, or MOL may directly repress biofilm formation.Conclusions/SignificanceMOL shows in vitro antimicrobial activity against clinical and standard S. aureus strains grown in planktonic and biofilm cultures, suggesting that the structure of MOL may potentially be used as a basis for the development of drugs targeting biofilms.

Highlights

Staphylococcus aureus (S. aureus) is one of the most important pathogens in both hospitals and communities and causes numerous diseases in humans, such as endocarditis, osteomyelitis and septicemia [1]
The growth curve of S. aureus ATCC 25923 demonstrated that MOL concentrations of 16, 32 and 64 mg/mL strongly inhibited the growth of planktonic bacteria (Fig. 1)
In S. aureus, cell death and lysis are controlled by the cid and lrg operons, the products of which are reported to function as holins and antiholins, respectively, and may serve as molecular control elements for bacterial cell lysis [38]

Summary

Introduction

Staphylococcus aureus (S. aureus) is one of the most important pathogens in both hospitals and communities and causes numerous diseases in humans, such as endocarditis, osteomyelitis and septicemia [1]. The biofilm structures are inherently resistant to antimicrobial challenge and are difficult to eradicate from the infected host [3]; there is clearly a need for novel antimicrobial agents with new mechanisms of action. Previous report showed that MOL inhibited biofilm formation by several bacteria, such as Streptococcus mutans, Streptococcus sanguis, Actinomyces naeslundii, Actinomyces viscosus, Enterococcus faecalis, and Fusobacterium nucleatum [7,8]. We found little data in the literature regarding the molecular mechanisms of MOL activity on bacteria grown in biofilm. The targeting of Staphylococcus aureus biofilm structures are gaining interest as an alternative strategy for developing new types of antimicrobial agents. Magnolol (MOL) shows inhibitory activity against S. aureus biofilms and Triton X-100-induced autolysis in vitro, there are no data regarding the molecular mechanisms of MOL action in bacteria

Methods

Results

Conclusion