Staphylococcus Aureus: The Bacterium Living on Your Skin

What is Staphylococcus Aureus?

Staphylococcus aureus is a gram-positive bacterium named for its golden color ("aureus" means golden in Latin) when grown in culture. It's one of the most common human pathogens, remarkable both for how harmlessly it lives on many of us and how deadly it can be when it invades.

About 30% of the population carries S. aureus in their nose (anterior nares), and about 20% carry it persistently.[2] Most carriers never develop disease; the bacterium simply coexists with the human microbiome. But when barriers are broken (through cuts, catheters, or surgery), staph can cause serious infections.

Clinical Infections

S. aureus causes an extraordinary range of infections, from minor to life-threatening:

Skin and Soft Tissue

Staph is the most common cause of bacterial skin infections:

• Folliculitis: Infection of hair follicles
• Furuncles (boils): Deep follicular infections
• Carbuncles: Clusters of connected boils
• Cellulitis: Spreading skin infection
• Impetigo: Superficial skin infection, common in children

Invasive Infections

When staph enters the bloodstream or deep tissues, it causes severe disease:

• Bacteremia: Bloodstream infection; can seed distant sites
• Endocarditis: Heart valve infection; often requires surgery
• Osteomyelitis: Bone infection
• Septic arthritis: Joint infection
• Pneumonia: Lung infection, often severe

Toxin-Mediated Disease

Some staph strains produce toxins that cause disease even without tissue invasion:

• Food poisoning: Preformed toxin causes rapid vomiting and diarrhea[4]
• Toxic shock syndrome: Superantigen-mediated shock and multi-organ failure
• Scalded skin syndrome: Toxin causes skin to peel in sheets (mostly in infants)

Staph Bacteremia

S. aureus bacteremia (SAB) is a particularly dangerous infection. Unlike many bloodstream infections that clear with antibiotics, staph tends to seed other sites in the body: heart valves, bones, joints, brain. Even with optimal treatment, mortality ranges from 20-30%.[1]

Management of SAB requires:

• Prolonged IV antibiotics (at least 2 weeks, often longer)
• Source control (removing infected catheters, draining abscesses)
• Echocardiogram to rule out endocarditis
• Infectious diseases consultation (shown to improve outcomes)

Treatment

Treatment depends on antibiotic susceptibility:

• MSSA (methicillin-susceptible): Nafcillin, oxacillin, or cefazolin
• MRSA (methicillin-resistant): Vancomycin, daptomycin, or linezolid[3]

Abscess drainage is crucial; antibiotics alone often fail without source control. For minor skin infections in healthy patients, incision and drainage may be sufficient without antibiotics.

Why Is Staph So Successful?

S. aureus has evolved an impressive arsenal of virulence factors:

• Protein A: Binds antibodies the "wrong way," preventing immune recognition
• Coagulase: Triggers clotting, creating protective fibrin barrier
• Biofilm formation: Creates communities resistant to antibiotics and immunity
• Immune evasion: Multiple mechanisms to hide from neutrophils and complement
• Persistence: Can survive inside host cells, causing relapsing infections

"Staph aureus is a master of survival. It can live peacefully on your skin, or invade and cause life-threatening infection. Understanding what tips the balance is key to prevention."

Prevention

Preventing staph infections focuses on:

• Hand hygiene: The single most important intervention
• Wound care: Cleaning and covering cuts
• Not sharing: Personal items like towels and razors
• Decolonization: Nasal mupirocin and chlorhexidine baths for carriers undergoing surgery
• Device management: Proper care of catheters and other invasive devices

Despite decades of research, there is no approved vaccine against S. aureus.[5] Multiple candidates have failed in clinical trials; the bacterium's sophisticated immune evasion mechanisms have proven formidable obstacles.