Andrographolide Sulfonate Is a Promising Treatment to Combat Methicillin-resistant Staphylococcus aureus and Its Biofilms

Lulu Zhang,Jianfeng Yi,Bo Wen,Weifeng Yang,Lang Lv,Yungchi Cheng,Yong Tan,Mei Bao,Cheng Lu,Qing Chen,Tariq Mahmood,Li Li,Ning Xie

doi:10.3389/fphar.2021.720685

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a drug-resistant pathogen threatening human health and safety. Biofilms are an important cause of its drug resistance and pathogenicity. Inhibition and elimination of biofilms is an important strategy for the treatment of MRSA infection. Andrographolide sulfonate (AS) is an active component of the traditional herbal medicine Andrographis paniculata. This study aims to explore the inhibitory effect and corresponding mechanisms of AS on MRSA and its biofilms. Three doses of AS (6.25, 12.5, and 25 mg/ml) were introduced to MRSA with biofilms. In vitro antibacterial testing and morphological observation were used to confirm the inhibitory effect of AS on MRSA with biofilms. Real-time PCR and metabonomics were used to explore the underlying mechanisms of the effect by studying the expression of biofilm-related genes and endogenous metabolites. AS displayed significant anti-MRSA activity, and its minimum inhibitory concentration was 50 μg/ml. Also, AS inhibited biofilms and improved biofilm permeability. The mechanisms are mediated by the inhibition of the expression of genes, such as quorum sensing system regulatory genes (agrD and sarA), microbial surface components–recognizing adhesion matrix genes (clfA and fnbB), intercellular adhesion genes (icaA, icaD, and PIA), and a gene related to cellular eDNA release (cidA), and the downregulation of five biofilm-related metabolites, including anthranilic acid, D-lactic acid, kynurenine, L-homocitrulline, and sebacic acid. This study provided valuable evidence for the activity of AS against MRSA and its biofilms and extended the methods to combat MRSA infection.

Highlights

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common drug-resistant bacteria, and MRSA infection has posed a serious threat to public health (Fulaz et al, 2020)
Tryptone and yeast extracts were obtained from Oxoid, United Kingdom, NaCl was obtained from Merck, Germany, and 2,3,5-triphenyltetrazolium chloride (TTC) was obtained from Amresco, United States. 2,3-Bis-(2-methoxy4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) and phenazine methosulfate (PMS) were purchased from Sigma-Aldrich, United States
Based on the minimum inhibitory concentration (MIC) results of Andrographolide sulfonate (AS), three concentrations of AS, 1/8 MIC, 1/4 MIC, and 1/2 MIC (6.25, 12.5, and 25 mg/ml), were selected for the XTT-PMS mixed solution (XTT) reduction assay on MRSA biofilms

Summary

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common drug-resistant bacteria, and MRSA infection has posed a serious threat to public health (Fulaz et al, 2020). Reduced antibiotic susceptibility contributes to the persistence of biofilm infections, forming a vicious cycle (Feng et al, 2020) This result explains why MRSA has acquired resistance to practically all antibiotics developed for clinical use in the past 50 years, including vancomycin (Van), which is the last resort to treating MRSA infection (Howden et al, 2010; McGuinness et al, 2017). Researchers have turned their attention to traditional medicine (TM), expecting to identify potential antibacterial drugs that will address the limitation that all antibiotics, including Van, are ineffective at removing mature biofilms (Chopra et al, 2015)

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