Mycobacterium houstonense

Mycobacterium houstonense

Mycobacterium houstonense is a member of the Mycobacterium fortuitum third biovariant complex. They are rapidly growing ubiquitous environmental organisms that normally inhabit soil, dust and water. These organisms frequently are human pathogens that cause a wide spectrum of clinically significant disease. It is important for practitioners to be aware of these organisms as possible etiological agents, as they are resistant to most first-line anti-tuberculous agents.


 * Etymology: houstonense pertaining to Houston, TX, USA, where the first isolate of the M. fortuitum third biovariant (sorbitol-positive) was identified.

Description
Microscopy
 * The organisms are acid-fast, Gram-positive, pleomorphic bacilli. Long filamentous forms are often observed, but the organisms have no spores or capsules.

Colony characteristics
 * Colonies are mucoid, convex, round and entire-edged and do not demonstrate aerial hyphae.
 * Colonies are white to slightly beige, small-diameter (approx. 1 mm) colonies after incubation on heart infusion agar with 5 % (v/v) rabbit blood for 2 days at 35 °C

Physiology
 * Growth on Löwenstein–Jensen medium at 35 and 42 °C in less than 7 days
 * Growth occurs on 5 % NaCl and on MacConkey's agar without crystal violet at 28 °C.
 * Semi-quantitative catalase of both isolates is weakly reactive (<45 mm).
 * The isolate has arylsulfatase activity by 3 days, utilize acetamide, reduce nitrate, exhibit iron uptake and produce urease and thermostable catalase.
 * It does not utilize citrate or grow in lysozyme.

Differential characteristics
 * The nearest phylogenetic neighbours, according to 16S rRNA gene sequence similarity, are M. fortuitum ATCC 6841T and M. senegalense ATCC 35796T.

Pathogenesis

 * Reported infections include skin and soft-tissue abscesses with associated osteomyelitis, bacteraemia, endocarditis, keratitis, lymphadenitis, peritonitis, post-surgical infections, pulmonary infections and disseminated disease. Involvement of the central nervous system is rare, but meningitis may develop after trauma or surgery. The immunocompromised patient is at special risk for developing severe diseases, especially catheter-related infection with bacteraemia.

Type Strain

 * The type strain, which was isolated from a face wound, is W5198T =ATCC 49403T =DSM 44676T.