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# 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

## Key points

- Catalase positive = staphylococcus; catalase negative = streptococcus or enterococcus.
- S. aureus: coagulase positive, beta-haemolytic, golden colonies, ferments mannitol.
- S. epidermidis: biofilm on catheters and prostheses; novobiocin sensitive.
- S. saprophyticus: cystitis in young sexually active women; novobiocin resistant.
- MRSA needs contact precautions.

## Microorganisms in this group

- [**Staphylococcus aureus** A common skin and nose bacterium that causes boils, cellulitis, bone infection, endocarditis and toxic shock; some strains are resistant (MRSA). Exam priority: high](https://durgical.com/en/microbiology/staphylococcus-aureus/)
- [**Staphylococcus epidermidis** A normal skin bacterium that infects catheters, prostheses and artificial valves by forming a sticky biofilm. Exam priority: medium](https://durgical.com/en/microbiology/staphylococcus-epidermidis/)
- [**Staphylococcus saprophyticus** A bacterium that causes urinary infection in young sexually active women; it is their second most common cause of community cystitis. Exam priority: medium](https://durgical.com/en/microbiology/staphylococcus-saprophyticus/)

## 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.

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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); [Urinary tract infection - adults](https://medlineplus.gov/ency/article/000521.htm) (MedlinePlus (NLM), 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/groups/staphylococci/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/groups/staphylococci/