Nanoscaled Discovery of a Shunt Rifamycin from Salinispora arenicola Using a Three-Color GFP-Tagged Staphylococcus aureus Macrophage Infection Assay

Antimicrobial resistance has emerged as a global publichealththreat, and development of novel therapeutics for treating infectionscaused by multi-drug resistant bacteria is urgent. Staphylococcus aureus is a major human and animalpathogen, responsible for high levels of morbidity and mortality worldwide.The intracellular survival of S. aureus in macrophages contributes to immune evasion, dissemination, andresilience to antibiotic treatment. Here, we present a confocal fluorescenceimaging assay for monitoring macrophage infection by green fluorescentprotein (GFP)-tagged S. aureus as afront-line tool to identify antibiotic leads. The assay was employedin combination with nanoscaled chemical analyses to facilitate thediscovery of a new, active rifamycin analogue. Our findings indicatea promising new approach for the identification of antimicrobial compoundswith macrophage intracellular activity. The antibiotic identifiedhere may represent a useful addition to our armory in tackling thesilent pandemic of antimicrobial resistance.