SYNOPSIS From Friend to Foe: Toxicity Trade-Offs Govern Staphylococcus aureus Infection Severity

Staphylococcus aureus is a nearly ubiquitous bacterium. Most of the time, it lives quietly and unnoticed as a member of the microbiota on your skin and in your nose. However, S. aureus— or “staph ” as it is commonly known—is an opportunistic pathogen, switching from friend to foe when it gets the chance. Some staph infections can be mild, local infections while in other instances it can lead to severe, life-threatening cases of pneumonia and bacteremia (blood infection) (Fig 1). When staph goes from being a mild-mannered microbiota member (a state known as car-riage) to an active infection, what governs whether it will be a minor or a major infection? Pre-vious research has implicated the secretion of toxins by staph as one of the determinants. These toxins are responsible for damaging local tissue, releasing nutrients to aid in bacteria Fig 1. Methicillin-resistant S. aureus (MRSA). S. aureus is a ubiquitous commensal bacterium and an opportunistic pathogen. When it acquires antibiotic resistance genes, it is extremely difficult to treat. Image credit: NIAID. doi:10.1371/journal.pbio.1002230.g00