SN7 SHORT NOTE 5M

Compare Actinomyces and Nocardia. Add a note on mycetoma.

Microbiology · 2nd Professional — Para-Clinical

Actinomyces

Gram-positive, branching, filamentous bacteria that resemble fungi but are true bacteria — they have peptidoglycan, no nucleus, and respond to antibiotics
Anaerobic or microaerophilic; non-acid-fast
Actinomyces israelii is the principal human pathogen; it is a normal commensal of the mouth, gut and female genital tract, so infection is endogenous and never transmitted between people
Sulphur granules — yellowish granules in the pus, consisting of colonies of the organism; crushed and stained they show gram-positive branching filaments with radiating clubs. They are the diagnostic finding
Molar tooth colonies on prolonged anaerobic culture, which requires up to 2 weeks

Form of actinomycosis	Features
Cervicofacial (about 60%)	The commonest; follows dental extraction, caries or trauma. A chronic indurated swelling at the angle of the jaw ("lumpy jaw") with multiple sinuses discharging sulphur granules; it crosses tissue planes and ignores anatomical barriers
Thoracic	After aspiration; chronic pneumonia with empyema and chest wall sinuses; may erode ribs, mimicking malignancy or tuberculosis
Abdominal	After appendicitis, perforation or surgery; an ileocaecal mass mimicking carcinoma or Crohn disease
Pelvic	Strongly associated with prolonged intrauterine contraceptive device use
Treatment	Prolonged high-dose penicillin for 6 to 12 months, with surgical drainage of abscesses and excision of sinuses; the long duration is essential because the dense fibrosis prevents drug penetration

CLINICAL PEARL

Actinomycosis crosses tissue planes, and that single behaviour is what suggests the diagnosis. Most infections respect anatomical boundaries and most tumours follow lymphatic routes. A chronic indurated lesion with multiple discharging sinuses that spreads directly through fascia, muscle and even bone, ignoring the usual barriers, is characteristic — and it is regularly mistaken for malignancy or tuberculosis until sulphur granules are looked for.

Nocardia

Feature	Actinomyces	Nocardia
Oxygen requirement	Anaerobic	Aerobic
Acid-fastness	Not acid-fast	Partially acid-fast — resists 1% sulphuric acid in the modified Ziehl-Neelsen stain (M. Tuberculosis resists 20%)
Source	Endogenous — normal flora of mouth and gut	Exogenous — free-living in soil and dust; acquired by inhalation or inoculation
Host	Usually immunocompetent	Usually immunocompromised — steroids, transplant, HIV, malignancy
Sulphur granules	Present and characteristic	Usually absent (present in mycetoma)
Chief disease	Cervicofacial actinomycosis	Pulmonary nocardiosis with a marked tendency to disseminate to the brain — so cerebral imaging is mandatory
Treatment	Penicillin, prolonged	CO-trimoxazole, prolonged (6 to 12 months)

Mycetoma

A chronic granulomatous infection of subcutaneous tissue characterised by the triad of painless swelling, multiple sinuses, and discharge containing grains; it destroys underlying bone
Actinomycetoma is caused by bacteria (Nocardia, Actinomadura, Streptomyces) and responds to antibiotics — co-trimoxazole with amikacin or dapsone
Eumycetoma is caused by fungi (Madurella) and requires antifungals with surgery, often amputation; the response is far poorer
The colour of the grains suggests the cause, and distinguishing the two is essential before treatment, since the management differs completely
"MADURA foot" takes its name from Madurai; the foot is the commonest site, following minor penetrating injury in people walking barefoot, and the condition remains endemic in parts of India and Africa

Applied Aspects

Look for sulphur granules in any chronic discharging sinus; the pus should be examined macroscopically and the granule crushed and stained, which is a cheap test that settles the diagnosis
Treat actinomycosis for months, not weeks; premature discontinuation is the commonest cause of relapse, and the fibrosis limits drug penetration
Image the brain in any patient with pulmonary nocardiosis, since cerebral abscess is common, frequently silent and alters both the drug choice and the duration
Consider nocardiosis in an immunosuppressed patient with pulmonary infiltrates not responding to standard antibiotics, and ask the laboratory to perform a modified Ziehl-Neelsen stain and to hold cultures longer
Distinguish actinomycetoma from eumycetoma before treating; a bacterial mycetoma is curable with antibiotics, whereas a fungal one often ends in amputation, so the distinction changes the patient's future
Footwear prevents mycetoma, and this is a simple and under-emphasised public health measure in the endemic belts of India

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