Identification of anti-virulence compounds for combating Staphylococcus aureus infections by highthroughput screening (HTS)

Abstract

Introduction: The indiscriminately use of antimicrobial drugs has led to the rapid emerging of multidrug resistant (MDR) bacteria including methicillin resistant Staphylococcus aureus (MRSA). Treatment by killing bacteria using antibiotics seems not to be an effective and sustainable way of controlling infections. Alternative ways for treating bacterial infections without incubating the emergence of drug resistant bacteria are highly valued. Objectives: Identification of therapeutic agents that suppress the expression and production of S. aureus virulence factors without inhibiting bacteria growth. Methods: The promoters of major virulence factors of S. aureus were cloned into a reporter vector using bacterial luciferase (Lux) and green fluorescent protein (GFP) as the reporter genes. Promoter activities were monitored by the measurement of luminescence and fluorescence readings. HTS of a chemical library with 50,240 compounds was carried out using S. aureus harboring an alpha-hemolysin gene (hla) promoter reporter plasmid and compounds that reduced the hla promoter activities considerably were selected as hits. Selected hit compounds were tested on other S. aureus virulence promoters for the identification of compounds that could suppress multiple virulence gene expressions. Compounds with potent suppressive effects on multiple virulence promoters were selected for further examinations using mammalian cell-based infection assays and mice in vivo infection models. Results: S. aureus hla promoter together with 14 other promoters of major virulence factors or virulence associated genes were successfully constructed. HTS of 50,240 compounds using the hla promoter-based reporter system yielded 670 hits that exerted suppressive effects in hla promoter activities. The anti-virulence activities of one compound were successfully demonstrated in mammalian cell-based infection assays and a mice in vivo infection model. Conclusion: HTS of 50,240 compounds were successfully implemented for the identification of anti-virulence compounds for S. aureus infections. Hit compounds with suppressive effects on multiple virulence gene promoters were identified and mammalian cell-based infection assays and a mice in vivo infection model showed the potential of applying anti-virulence compounds in treating S.aureus and other bacterial infections.