Actinomyces israelii

Actinomyces israelii is a bacterium that normally lives harmlessly in the mouth and gut but can cause a slow-growing, chronic infection called actinomycosis if it enters deeper tissues, often after injury, surgery, or dental procedures.

Infection typically occurs when the bacterium breaches normal mucosal barriers, such as after dental work, jaw trauma, aspiration into the lungs, or use of certain intrauterine devices, allowing it to invade deeper tissue.

Symptoms depend on location but often include a slow-growing, painless or mildly painful lump, chronic drainage of pus through the skin (sinus tracts), and sometimes low-grade fever and weight loss.

It is not usually life-threatening but can cause significant, progressive tissue damage if untreated, as it tends to spread slowly into surrounding structures, mimicking a tumour on imaging.

Yes, it responds well to prolonged antibiotic treatment, usually penicillin-based, and most people achieve a full cure, though treatment duration is much longer than for typical bacterial infections.

Treatment involves a prolonged course of antibiotics, often several weeks to months, sometimes combined with surgical drainage or removal of affected tissue if there's a significant abscess or mass.

Antibiotic courses typically last from a few weeks up to six months or more, depending on the extent of infection, reflecting the slow-growing nature of the bacterium.

Actinomycosis can closely mimic a tumour on imaging due to its slow-growing, invasive appearance, but a biopsy showing characteristic bacterial colonies (sulfur granules) and response to antibiotics confirms infection rather than cancer.

Diagnosis usually requires tissue biopsy or culture showing the characteristic bacteria, as imaging alone often cannot distinguish it from a tumour or other chronic infection.

See a doctor for a persistent, unexplained lump or drainage, especially after dental work or trauma. NHS referral timing depends on urgency, while private specialist assessment is often available within about one to two weeks.