[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Staphylococci](https://durgical.com/en/microbiology/groups/staphylococci/) › Staphylococcus aureus [Microbiology](https://durgical.com/en/microbiology/) · [Staphylococci](https://durgical.com/en/microbiology/groups/staphylococci/) # Staphylococcus aureus - Bacterium - Gram-positive - Contact - Exam priority: high A common skin and nose bacterium that causes boils, cellulitis, bone infection, endocarditis and toxic shock; some strains are resistant (MRSA). Updated 2026-11-01 Also called: golden staph, MRSA (methicillin-resistant), MSSA (methicillin-susceptible) ## Key points - Catalase positive + coagulase positive = S. aureus. - MRSA: mecA encodes PBP2a, which binds beta-lactams poorly. - TSST-1 is a superantigen: toxic shock (tampons, nasal packing, wounds). - Food poisoning from preformed toxin: vomiting within hours. - Leading cause of osteomyelitis and acute endocarditis; tricuspid valve in people who inject drugs. ## At a glance **Gram** Gram-positive **Shape** Cocci in clusters **Oxygen** Facultative anaerobe **Family** Staphylococcaceae **Stain** Gram positive; catalase and coagulase positive ## Morphology - Gram-positive cocci in grape-like clusters - Golden, beta-haemolytic colonies on blood agar - Ferments mannitol on mannitol salt agar ## Transmission - Direct contact with infected skin or with carriers (nostrils) - Contaminated objects and surfaces - Health-care workers' hands in hospital - Food carrying preformed enterotoxin (food poisoning) ### Isolation precautions What the care team adds to standard precautions. **Contact** Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing. ## Virulence factors - Protein A: binds the Fc portion of IgG and blocks opsonisation - Coagulase: builds a fibrin coat that shields the bacterium - TSST-1 and enterotoxins: superantigens that switch on T cells en masse - Heat-stable enterotoxins: vomiting a few hours after a meal - Exfoliative toxins: scalded skin syndrome in children - Panton-Valentine leukocidin: kills white cells; linked to community MRSA ## Diseases it causes - Cellulitis, boils and skin abscesses [Cellulitis of the leg →](https://durgical.com/en/conditions/cellulitis-of-the-leg/) - Osteomyelitis (leading cause) [Osteomyelitis →](https://durgical.com/en/conditions/osteomyelitis/) - Septic arthritis [Septic Arthritis of the Knee →](https://durgical.com/en/conditions/septic-arthritis-of-the-knee/) - Infective endocarditis, especially in people who inject drugs [Infective endocarditis →](https://durgical.com/en/conditions/infective-endocarditis/) - Toxic shock syndrome [Toxic shock syndrome →](https://durgical.com/en/conditions/toxic-shock-syndrome/) - Breast abscess and mastitis [Breast abscess →](https://durgical.com/en/conditions/breast-abscess/) - Impetigo, alone or with S. pyogenes [Impetigo →](https://durgical.com/en/conditions/impetigo/) ## Clinical picture - A fluctuant abscess full of pus - Fever, low blood pressure and a red rash that peels on palms and soles (toxic shock) - Sudden vomiting soon after eating (food poisoning) ## Diagnosis - Gram stain: Gram-positive cocci in clusters - Catalase positive and coagulase positive - Culture on blood agar and mannitol salt agar - mecA or PBP2a detection to confirm MRSA - Blood cultures when bacteraemia or endocarditis is suspected ## Treatment MSSA: anti-staphylococcal penicillins (oxacillin) or first-generation cephalosporins (cefazolin). MRSA: vancomycin, linezolid or daptomycin depending on the site; clindamycin and other oral agents are also used for skin infection. MRSA resists nearly all beta-lactams through PBP2a; draining abscesses is part of treatment. Drug class only; doses and regimens are set by the clinician from the current guideline. In Pharmacology: - [Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/) - [Oxacillin](https://durgical.com/en/pharmacology/oxacillin/) - [Cefazolin](https://durgical.com/en/pharmacology/cefazolin/) - [Vancomycin](https://durgical.com/en/pharmacology/vancomycin/) - [Linezolid](https://durgical.com/en/pharmacology/linezolid/) - [Daptomycin](https://durgical.com/en/pharmacology/daptomycin/) - [Clindamycin](https://durgical.com/en/pharmacology/clindamycin/) ## Prevention - Hand hygiene - Covering draining wounds - Contact precautions for patients with MRSA - No sharing of towels or personal items ## In Colombia Community-onset MRSA circulates in Colombia and causes skin and soft-tissue infections in people with no previous hospital contact. ## Memory aid Picture a golden knight with a shield (protein A) and a fibrin cloak (coagulase): it hides from the immune system and settles wherever it lands. ## Test yourself Think of the answer, then tap the question to see it. ## Which gene explains MRSA's resistance to methicillin? mecA, which encodes PBP2a, a penicillin-binding protein with low affinity for beta-lactams. ## Which S. aureus toxin causes toxic shock syndrome? TSST-1, a superantigen that massively activates T cells and releases cytokines. ## Why does S. aureus food poisoning start so quickly? Because the heat-stable enterotoxin is already formed in the food; the bacterium does not need to grow in the gut. ## Which precautions does nursing apply to a patient with MRSA? Standard precautions plus contact precautions: gown and gloves, dedicated equipment and hand hygiene. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/staphylococcus-aureus/) ## Related - [Staphylococcus epidermidis](https://durgical.com/en/microbiology/staphylococcus-epidermidis/) - [Streptococcus pyogenes](https://durgical.com/en/microbiology/streptococcus-pyogenes/) ## Related conditions - [Cellulitis of the leg](https://durgical.com/en/conditions/cellulitis-of-the-leg/) - [Osteomyelitis](https://durgical.com/en/conditions/osteomyelitis/) - [Septic Arthritis of the Knee](https://durgical.com/en/conditions/septic-arthritis-of-the-knee/) - [Infective endocarditis](https://durgical.com/en/conditions/infective-endocarditis/) - [Toxic shock syndrome](https://durgical.com/en/conditions/toxic-shock-syndrome/) - [Breast abscess](https://durgical.com/en/conditions/breast-abscess/) - [Impetigo](https://durgical.com/en/conditions/impetigo/) ## What the colours mean **Gram-positive** Thick peptidoglycan wall: stains purple. **Gram-negative** Thin wall with an outer membrane: stains pink. **Acid-fast** Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain. **Contact** Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing. **Droplet** Surgical mask within about a metre; single room. **Airborne** N95 respirator and a negative-pressure room. [← Back to the group: Staphylococci](https://durgical.com/en/microbiology/groups/staphylococci/) Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Methicillin-resistant Staphylococcus aureus (MRSA) Basics](https://www.cdc.gov/mrsa/about/index.html) (CDC, 2025); [Staphylococcal Infections](https://medlineplus.gov/staphylococcalinfections.html) (MedlinePlus (NLM), 2025); [Toxic shock syndrome: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000653.htm) (MedlinePlus (NLM), 2024); [Food poisoning: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/001652.htm) (MedlinePlus (NLM), 2024). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/microbiology/staphylococcus-aureus/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/staphylococcus-aureus/