Mycobacterium kansasii

Overview
Mycobacterium kansasii

Description
Gram-positive, nonmotile, moderately long to long and acid-fast rods.

Colony characteristics
 * Smooth to rough colonies after 7 or more days of incubation.
 * Colonies grown in dark are nonpigmented, when grown in light or when young colonies are exposed briefly to light, colonies become brilliant yellow (photochromogenic).
 * If grown in a lighted incubator, most strains form dark red crystals of β-carotene on the surface and inside of colony.

Physiology
 * Growth on Middlebrook 7H10 agar at 37°C within 7 days or more.
 * Resistant to isoniazid.
 * Susceptible to ethambutol.

Differential characteristics
 * Closely related to the non-pathogenic, also slowly growing, nonpigmented M. gastri.
 * Both species share an identical 16S rDNA but differentiation is possible by differences in the ITS and hsp65 sequences
 * A commercial hybridisation assay (AccuProbe) to identify M. kansasii exists.

Pathogenesis

 * Chronic human pulmonary disease resembling tuberculosis (involvement of the upper lobe).
 * Extrapulmonary infections, (cervical lymphadenitis in children, cutaneous and soft tissues infections and musculoskeletal system involvement), are uncommon.
 * Rarely causes disseminated disease except in patients with severely impaired cellular immunity (patients with organ transplants or AIDS).
 * Normally considered not to be contagious from person to person.
 * Natural sources of infections unclear. Tap water is believed to be the major reservoir associated with human disease.
 * Biosafety level 2

Type Strain
Strain ATCC 12478 = CIP 104589 = DSM 44162 = JCM 6379 = NCTC 13024.
 * First and most frequently isolated from human pulmonary secretions and lesions.