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Home Books Jawetz, Melnick, & Adelberg’s Medical Microbiology, 27e

Chapter 23: Mycobacteria

INTRODUCTION

The mycobacteria are rod-shaped, aerobic bacteria that do not form spores. Although they do not stain readily, after being stained, they resist decolorization by acid or alcohol and are therefore called “acid-fast” bacilli. Mycobacterium tuberculosis causes tuberculosis and is a very important pathogen of humans. Mycobacterium leprae causes leprosy. Mycobacterium avium-intracellulare (M avium complex, or MAC) and other nontuberculous mycobacteria (NTM) frequently infect patients with AIDS, are opportunistic pathogens in other immunocompromised persons, and occasionally cause disease in patients with normal immune systems. There are more than 200 Mycobacterium species, including many that are saprophytes. The mycobacteria that infect humans are listed in Table 23-1.

TABLE 23-1Mycobacteria That Infect Humans
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TABLE 23-1 Mycobacteria That Infect Humans
Species Reservoir Common Clinical Manifestations; Comment
SPECIES ALWAYS CONSIDERED PATHOGENS

Mycobacterium tuberculosis

Mycobacterium leprae

Mycobacterium bovis

Humans

Humans

Humans, cattle

Pulmonary and disseminated tuberculosis; millions of cases annually in the world

Leprosy

Tuberculosis-like disease; rare in North America; M bovis is closely related to M tuberculosis
SPECIES POTENTIALLY PATHOGENIC IN HUMANS
Moderately common causes of disease
 Mycobacterium avium complex Soil, water, birds, fowl, swine, cattle, environment Disseminated, pulmonary; very common in untreated AIDS patients; occurs in other immunosuppressed patients; uncommon in patients with normal immune systems
 Mycobacterium kansasii Water, cattle Pulmonary, other sites
Uncommon to very rare causes of disease
 Mycobacterium africanum Humans, monkeys Pulmonary cultures; resembles M tuberculosis; rare
 Mycobacterium genavense Humans, pet birds Blood in AIDS patients; grows in liquid medium (BACTEC) and on solid medium supplemented with mycobactin J; grows in 2–8 weeks
 Mycobacterium haemophilum Unknown Subcutaneous nodules and ulcers primarily in AIDS patients; requires hemoglobin or hemin; grows at 28°–32°C; rare
 Mycobacterium malmoense Unknown, environment Pulmonary, tuberculosis-like (adults), lymph nodes (children); most reported cases are from Sweden, but organism may be much more widespread; M malmoense is closely related to Mycobacterium avium-intracellulare; takes 8–12 weeks to grow
 Mycobacterium marinum Fish, water Subcutaneous nodules and abscesses, skin ulcers
 Mycobacterium scrofulaceum Soil, water, moist foods Cervical lymphadenitis; usually cured by incision, drainage, and removal of involved lymph nodes
 Mycobacterium nonchromogenicum Environment The primary pathogen in the Mycobacterium terrae complex. Causes tenosynovitis of the hand

 Mycobacterium simiae

(new members of M simiae complex include M lentiflavum, M triplex, M europaeum)

 Monkeys, water Pulmonary, disseminated in AIDS patients; rare
Mycobacterium szulgai Unknown Pulmonary, tuberculosis-like; rare
Mycobacterium ulcerans Humans, environment Subcutaneous nodules and ulcers; may be severe; M ulcerans is closely related to M marinum; takes 6–12 weeks to grow; optimal growth at 33°C suggests environmental source; rare
Mycobacterium xenopi Water, birds Pulmonary, tuberculosis-like with preexisting lung disease; rare
Rapid growers
Mycobacterium abscessus Soil, water, animals Most frequently isolated rapid grower from pulmonary infections; skin and soft tissue infections; frequently multidrug resistant
Mycobacterium chelonae Soil, water, animals, marine life Cutaneous lesions most common, subcutaneous abscesses, disseminated infections in immunocompromised ...

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