Electron Transport-DeficientStaphylococcus aureusSmall-Colony Variants as Emerging Pathogens

Abstract

A pathogenic organism can be seen as an ‘‘emerging’’ pathogen in several ways. It may be a newly discovered organism, an organism that has acquired new virulence factors or antibiotic resistance, or a well-known pathogen for which newly discovered subpopulations of the parent strain are able to produce disease. Staphylococcus aureus small-colony variants (SCVs) fall into the last category. In S. aureus SCVs, reversal of the SCV phenotype by adding compounds that can be utilized to repair the defect in electron transport simultaneously or by complementing the genetic defect in trans enhances alpha-toxin production. Well-characterized S. aureus hemin biosynthetic mutants demonstrate an SCV phenotype, including decreased coagulase activity, aminoglycoside resistance, decreased pigmentation, slow growth, and reduced hemolytic activity. Anaerobic growth downregulates menaquinone biosynthesis in S. aureus and electron transport. Taken together, these observations show that alpha-toxin production is dependent upon electron transport. Carotenoid pigments that give S. aureus SCV colonies their characteristic yellow color require ATP for their biosynthesis. Aminoglycoside uptake by S. aureus is an energy-dependent process that requires ATP and an electrochemical gradient, which is produced via the electron transport system.