Actinomyces and Nocardia genera, atypical and apathogenic Mycobacteria

Question 1

General features and habitat of Actinomyces israelii

Answer 1

Gram +
Branching, filamentous rod
Habitat- normal flora of oral cavity of human and animals and female genital tract

Question 2

Biochemical Properties of Actinomyces israelii

Answer 2

Obligate anaerobe (used to distinguish between Nocardia)

Question 3

Pathogenesis of Actinomyces israelii

Answer 3

If oral tissue is injured, e.g. jaw trauma or dentist’s work, it spreads to head and neck.

Cervico-Facial infection:
involve the face, neck, jaw, or tongue and usually occur following an injury to the mouth or jaw or a dental manipulation such as extraction; the disease begins with pain and firm swellings (lumps) along the jaw and slowly progresses until draining sinuses are produced

Thoracic infection:
Initiated by aspiration of pieces of infectious material from the teeth. May involve chest wall, the lungs, or both

Abdominal infection:
Initiated by abdominal surgery, accidental trauma or acute perforated GI disease. May be also from female pelvic infection associated with intrauterine contraceptive device

Question 4

Clinical Features (Actinomycosis) of Actinomyces israelii

Answer 4

Begins with firm lumps (e.g. on the jaw in case of cerbico-facial), eventually forming suppurative abscesses or granulomas in chronic infection.

This is followed by the formation of draining sinuses (in long standing cases) that spread the infection through the skin and further to the body, forming firm thick yellow pus (sulfur granules), where the bacteria are found

Question 5

Diagnosis of Actinomyces israelii

Answer 5

Oxygen-tolerant anaerobic culture (around 1 week of cultivation)

Sulfur exudate can be used for microscopy diagnosis

Question 6

Treatment of Actinomyces israelii

Answer 6

Penicillin- long term

Surgical drainage and excision of damaged tissue

Question 7

General features and habitat of Nocardia Genus

Answer 7

Gram + (stains weakly with Gram staining) Branching, filamentous rod

found in soil

Question 8

Biochemical Properties of Nocardia Genus

Answer 8

Obligate aerobe (used to distinguish between Actinomyces israelii)
Catalase +
Urease +

Question 9

Pathogenesis of Nocardia Genus

Answer 9

Transmitted by air or traumatic transplantation

Affects immunocompromised (e.g. HIV, glucocosteroid drugs) and cancer patients

Affects more men than women

Question 10

Clinical Features (Nocardiosis) of Nocardia Genus

Answer 10

Pulmonary- 90% (can be acute, subacute or chronic)

Pneumonia (local or diffuse) with cavitation
Lung abscesses
Coughing, fever, dyspnea
Radiological abnormalities- nodules and nodular infiltration

Cutaneous- 20% (by exposing to dirt)
Firm, thick lesions (localized) and inflammatory reaction of abscesses with granules in skin (disseminated)

CNS (if hematogenous spreading to brain from lungs)
Brain abscesses with multiple foci

Question 11

Diagnosis of Nocardia Genus

Answer 11

Culture of sputum or pus from cutaneous lesion (slowly growing)

Weakly Acid-Fast staining (Ziehl-Neelsen staining)- contain carbol fuchsin, that can be taken up by the cell wall if it has mycolic acids (long chain fatty acid with two tails)

Gram staining- can be used but stains weakly

Question 12

Treatment of Nocardia Genus

Answer 12

Sulfonamides i.e. Trimethoprim and Sulfamethoxazole (TMP-SMX)- long term
Surgical drainage

Question 13

Apathogenic Mycobacteria

Answer 13

For example: M. smegmatis- does not cause human disease

Question 14

Atypical Mycobacteria

Opportunistic Pathogen

Answer 14

Known as non-tuberculous Mycobacteria.
Clinical manifestations:
May produce a wide range of clinical conditions
Pulmonary disease caused by these organisms is virtually indistinguishable from tuberculosis
Disseminated infection is usually limited to immunocompromised patients only

Question 15

Runyon Classification

Answer 15

Based on rate of growth, production of yellow pigment and if it was produced in dark when exposed to light:

Question 16

Group I

Answer 16

Slow growers, photo-chromogens, pigmented only when exposed to light

M. marinum
Source: sweet and salt water, fishes

Disease: lung-TB (especially in immunocompromised, i.e. AIDS patients)

Question 17

Group II

Answer 17

Slow growers, scoto-chromogens, form pigment in the dark

M. scrofulaceum
Source: soil, water

Pathogeneisis: enter through the oropharynx, usually in children

Disease: granulomatous cervical lymphadenitis (treat by surgical removal)

Question 18

Group III

Answer 18

Slow growers, non-chromogens, rarely pigmented

M. ulcerans
Source: soil, water

Disease: skin lesions, abscesses (“Buruli ulcer”)

Question 19

Group IV

Answer 19

Rapid growers (<7 days)

M. chelonae
Source: soil, water and animals

Disease: subcutaneous tissues lesions (when injured by trauma), rarely causes disseminated infections