# Actinomycosis and Nocardiosis

> Actinomycosis and nocardiosis for NEET-PG Medicine covering sulphur granules, partially acid-fast filaments, cervicofacial disease and antibiotic therapy.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/actinomycosis-and-nocardiosis
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Harrison's Principles of Internal Medicine; Mandell's Principles and Practice of Infectious Diseases; Ananthanarayan and Paniker's Textbook of Microbiology
- How to cite: "Actinomycosis and Nocardiosis", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/actinomycosis-and-nocardiosis

## Direct answer
Actinomycosis and nocardiosis are chronic suppurative infections caused by filamentous Gram-positive bacteria, with Actinomyces israelii responsible for actinomycosis and Nocardia species for nocardiosis. Actinomycosis classically produces yellow sulphur granules in pus, while Nocardia shows partially acid-fast branching filaments and tends to affect immunosuppressed patients through the lungs or brain. Penicillin treats actinomycosis, and cotrimoxazole is the standard choice for nocardiosis.

## What you must remember
- **Sulphur granules:** Yellow, grain-like clusters in pus made of Actinomyces colonies with club-shaped hyphae at the periphery; they are not elemental sulphur.
- **Cervicofacial actinomycosis:** The commonest form, often after dental extraction or trauma, with woody induration and discharging sinuses.
- **Thoracic and abdominal actinomycosis:** Thoracic disease may follow aspiration, and abdominal disease may follow appendicitis or intrauterine device use.
- **Treatment of actinomycosis:** Prolonged high-dose penicillin with surgical drainage of collections, so the course is measured in months.
- **Nocardia:** Aerobic and partially acid-fast on modified Ziehl-Neelsen stain, causing pulmonary, cutaneous and cerebral disease, especially in immunosuppressed hosts.
- **Treatment of nocardiosis:** Cotrimoxazole is the drug of choice, with imipenem, amikacin or linezolid as alternatives in severe or sulfonamide-intolerant disease, and brain abscesses need drainage.

## A worked pathway: a steroid-treated patient with a lung lesion

A 52-year-old man on long-term prednisolone for a connective tissue disorder presents with fever, productive cough, lung consolidation and a subcutaneous nodule on the forearm.

1. **Stain the sputum:** A modified Ziehl-Neelsen stain shows beaded, branching, partially acid-fast filaments, which points towards Nocardia and away from Mycobacterium tuberculosis.
2. **Start cotrimoxazole early:** Culture takes several days, so cotrimoxazole is begun empirically while the diagnosis is still unproven.
3. **Image the brain:** Nocardia disseminates to the brain in immunosuppressed patients, so brain imaging is done and any abscess is considered for drainage.
4. **Monitor the drug:** Renal function and potassium are checked during cotrimoxazole, since creatinine can rise and hyperkalaemia can occur.
5. **Choose alternatives if needed:** If sulfonamides are not tolerated, imipenem, amikacin or linezolid is chosen after specialist advice.
6. **Treat for months:** Therapy continues for many months, guided by clinical response and imaging, which confirms resolution before the course is stopped.

## Where the exam tries to catch you

Examiners exploit look-alike features and drug swaps.

- **Trap:** Treating a Nocardia lung lesion as tuberculosis because both are acid-fast to some degree — **Correct:** Nocardia is only partially acid-fast and needs cotrimoxazole, so antitubercular drugs waste time.
- **Trap:** Giving cotrimoxazole for actinomycosis — **Correct:** Actinomyces israelii is an anaerobic, non-acid-fast organism treated with prolonged penicillin, and recurrence is prevented by drainage and dental source control.
- **Trap:** Calling every grain-bearing sinus actinomycosis — **Correct:** Sulphur granules must be distinguished from mycetoma grains, which have a different clinical picture, though actinomycotic mycetoma can be caused by Nocardia.

A cervicofacial lesion should never be expected to show acid-fast organisms.

## Frequently asked questions

### What is the drug of choice for nocardiosis?
Cotrimoxazole, which combines trimethoprim and sulfamethoxazole, is the drug of choice for nocardiosis. Duration is usually prolonged, particularly for brain or disseminated disease, and alternatives such as imipenem, amikacin or linezolid are used when sulfonamides cannot be given.

### Which organism causes sulphur granules, and where does it typically infect?
Actinomyces israelii causes sulphur granules, and infection classically involves the cervicofacial region after dental trauma. It also affects the thorax and abdomen, and the lesions form sinus tracts that discharge pus containing yellow granules.

### Why is Nocardia called partially acid-fast?
Nocardia resists decolourisation by weak acid (1 per cent sulphuric acid) but loses the carbol fuchsin with strong acid-alcohol, so it is described as partially acid-fast on a modified Ziehl-Neelsen stain. This differs from fully acid-fast Mycobacterium tuberculosis and is a key laboratory clue in vignettes.

### Which antibiotic is used for cervicofacial actinomycosis?
High-dose penicillin is the standard antibiotic for cervicofacial actinomycosis, given intravenously first and then orally for a prolonged period, usually months. Surgical drainage of collections and dental source control are also part of management.