Actinomyces israelii

1. GC 101 (Diagnosis of Infections) emphasises that prolonged anaerobic culture is essential — standard short-incubation aerobic cultures will miss Actinomyces ^[1]. This is a common exam pitfall: a "culture-negative" chronic abscess with sulfur granules should prompt request for extended anaerobic incubation.

2. GC 105 (Medically Important Microbes) lists Actinomyces israelii among important anaerobic bacteria every doctor should know ^[4]. Key teaching: it is a bacterium, NOT a fungus — despite the "-mycosis" suffix.

3. GC 219 (Infections and Tumours in Pharynx and Oral Cavity): cervicofacial actinomycosis is the classic oral/pharyngeal infection that presents as a chronic draining jaw lesion after dental procedures ^[5]. Examiners may present a post-dental-extraction jaw mass with draining sinuses — the answer is Actinomyces israelii.

4. Ryan Ho Neurology notes include Actinomyces as a cause of chronic meningitis and brain abscess ^[3] — this is a less common but examinable presentation, especially in the differential of chronic/subacute CNS infections alongside TB and Cryptococcus.

5. GC 071 (It is Red and Painful) — in the context of chronic soft-tissue infection with sinus formation, Actinomyces should be considered alongside TB and atypical mycobacteria ^[6]. The distinguishing feature is sulfur granules.

6. AOS Microbiology: Actinomyces is classically tested as "the anaerobic branching G+ve rod that is NOT acid-fast" — the single most important discriminator from Nocardia ^[7].

• Vignette clue "sulfur granules" → always Actinomyces, never Nocardia.
• "Crosses tissue planes" is a classic phrase examiners use to hint at actinomycosis.
• IUD + pelvic abscess in a woman → think Actinomyces before thinking malignancy.
• Chronic lung mass mimicking carcinoma with chest wall sinus → thoracic actinomycosis; examiners may present imaging that looks like bronchogenic CA.

No directly relevant past paper questions specifically examining Actinomyces israelii were identified in the indexed past paper context (2016–2025 Fourth Summative papers). However, note the following related stems:

• 2023 Fourth Summative Minicase Q9 ^[8]: "Name three microorganisms that can commonly cause infective spondylitis" — the expected answers include S. aureus, M. tuberculosis, and Brucella/Salmonella. Actinomyces is NOT a standard answer here but may appear as a distractor for chronic bone infections.

• The concept of chronic meningitis aetiology (where Actinomyces appears in Ryan Ho's list ^[3]) is fair game for SAQ questions asking for differential diagnoses of chronic/subacute meningitis — alongside TB, Cryptococcus, Brucella, and malignant meningitis.