Staphylococci !
- Bacteria
Gram-positive cocci in clusters that live on skin and in the nose; S. aureus is the most aggressive and MRSA the most feared in hospitals.
Updated 2026-11-01
What they are
Staphylococci are Gram-positive cocci that grow in grape-like clusters and are catalase positive, which separates them from streptococci. Coagulase splits the genus: S. aureus is coagulase positive, while the others (S. epidermidis, S. saprophyticus) are coagulase negative. All are part of the normal flora of skin and mucosa.
What they share
- Cocci in clusters, catalase positive
- Coagulase positive only in S. aureus
- Salt tolerant: grow on mannitol salt agar
- Methicillin resistance through the mecA gene (PBP2a)
- Colonise skin and nostrils
Microorganisms in this group
- Staphylococcus aureusA common skin and nose bacterium that causes boils, cellulitis, bone infection, endocarditis and toxic shock; some strains are resistant (MRSA).Exam priority: high
- Staphylococcus epidermidisA normal skin bacterium that infects catheters, prostheses and artificial valves by forming a sticky biofilm.Exam priority: medium
- Staphylococcus saprophyticusA bacterium that causes urinary infection in young sexually active women; it is their second most common cause of community cystitis.Exam priority: medium
Test yourself
Think of the answer, then tap the question to see it.
Which biochemical test separates staphylococci from streptococci?
Catalase: staphylococci produce it (bubbles with hydrogen peroxide) and streptococci do not.
Which test distinguishes S. aureus from the other staphylococci?
Coagulase: S. aureus is coagulase positive; S. epidermidis and S. saprophyticus are coagulase negative.
How are S. epidermidis and S. saprophyticus told apart in the lab?
With novobiocin: S. epidermidis is sensitive and S. saprophyticus is resistant.
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 (CDC, 2025); Staphylococcal Infections (MedlinePlus (NLM), 2025); Urinary tract infection - adults (MedlinePlus (NLM), 2024).
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Representative model, for educational purposes only.