Non-tuberculous mycobacteria

Dr. Pendru Raghunath Reddy

Mycobacteria other than mammalian tubercle bacilli, which may occasionally cause human disease are called ‘non-tuberculous mycobacteria’

Other names include atypical mycobacteria, anonymous, unclassified Mycobacteria and Mycobacteria other than M. tuberculosis (MOTT)

Runyoun classificationNTM have been categorized into four groups by Runyoun (1959) based on pigment production and the growth rate

1. Photochromogenes

2. Scotochromogens

3. Non-photochromogens

4. Rapid growers

Runyon Group Number

Group Name Description

I Photochromogens Colonies of NTM that develop pigment following exposure to light after being grown in the dark and take more than 7 days to appear on solid media

II Scotochromogens Colonies of NTM that develop pigment in the dark or light and take more than 7 days to appearon solid media

III Nonphotochromogens Colonies of NTM that are nonpigmented regardless of whether they are grown in the dark or lightand take more than 7 days to appear on solid media

IV Rapid-growers Colonies of NTM that appear on solid media in less than 7 days

They are not usually transmitted from person to person

Source of infection is water, soil, food and animals

Human infection with NTM is common in some areas, disease is rare

Exhibits dysgonic growth on LJ medium

Niacin and nitrate reduction tests are negative

Not able to cause progressive disease in guniea pigs

Photochromogens

The important species in this group are M. kansasii, M. marinum and M. simiae

M. kansasii

M. kansasii causes chronic pulmonary disease resembling tuberculosis

It may also occasionally cause infections of the cervical lymphnodes, penetrating wound infections and granulomatous synovitis

It can produce generalized infection in HIV patients

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Mycobacterium marinum

Causes a warty skin lesion known as swimming pool or fish tank granuloma

Closely resembles M. kansasii but can be differentiated by its poor growth at 370C, negative nitratase, and positive pyrazinamide hydrolase

Fish tank granuloma

Scotochromogens

These strains form pigmented colonies (yellow-orange-red) even in the dark

They are widely distributed in the environment and sometimes contaminate cultures of tubercle bacilli

Important species in this group:

M. scrofulaceum may cause scrofula (cervical adenitis) in children

M. gordonae often found in tap water is a common contaminant in clinical specimens and a rare cause of pulmonary disease

M. szulgai, an uncommon cause of pulmonary disease and bursitis

It is a scotochromogen when incubated at 370C but a photochromogen at 250C

Scrofula (cervical adenitis)

Non-photochromogens

Medically important species in this group are M. avium, M. intracellulare, M. xenopi and M. ulcerans

M. avium

Which causes natural tuberculosis in birds and lymphadenopathy in pigs, is one of the most common opportunistic human pathogens

M. intracellulare

Is commonly known as Battey bacillus

M. avium and M. intracellulare are so similar that that they have been considered as one group, the M. avium complex (MAC)

MAC complex cause lymphadenopathy, pulmonary lesions or disseminated disease, particulary in AIDS patients

M. xenopi, originally isolated from toads, may occasionally cause chronic lung disease in human beings

M. ulcerans cause buruli ulcer

Rapid growers

This is a heterogeneous group of mycobacteria capable of rapid growth, colonies appearing within 7 days of incubation at 370C or 250C

Within the group, photochromogenic, scotochromogenic, and non-chromogenic species occur

Most of these are purely are environmental saprophytes

The medically important species are M. fortuitum and M. chelonae

M. fortuitum and M. chelonae occasionally cause pulmonary or disseminated disease but are principally responsible for postinjection abscesses and wound infections

Outbreaks of abscesses following injections of vaccines contaminated by these mycobacteria have been reported

Lesions produced by NTM

1. Localized lymphadenitis

2. Skin lesions (Postinjection abscesses, swimming pool granuloma and buruli ulcer)

3. Tuberculosis-like pulmonary lesions

4. Disseminated disease

Swimming pool granuloma

It is caused by M. marinum and is also known as fish tank granuloma

M. marinum occurs as a saprophyte in fresh or salt water

Human infection originates from contaminated swimming pools or fish tanks

The bacilli enter scratches and abrasions and cause warty lesions similar to those seen in skin tuberculosis

The lesion, beginning as a papule and break down to form an indolent ulcer

The disease is usually self-limiting although chemotherapy with minocycline, cotrimoxazole or rifampicin with ethambutol hastens its resolution

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Buruli ulcer

This disease is caused by M. ulcerans

The name is derived from the Buruli district of Uganda where a large outbreak was extensively investigated

Ulcers are usually seen on the legs or arms and are believed to follow infection through minor injuries

After an incubation period of a few weeks, indurated nodules appear, which break down forming indolent ulcers which slowly extend under the skin

When the immunoreactive phase sets in ulcers heal with disfiguring scars

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