Mycobacterium tusciae is a slow-growing, scotochromogenic
mycobacterium first isolated from a lymph node of an immunocompromised child and subsequently from tap water and from a respiratory specimen of a patient with chronic fibrosis.
Etymology: tusciae referring to the Italian region of Tuscany, where the organisms were first isolated.
Description
Microscopy
Gram-positive, nonmotile and acid-fast rods.
Early
microscopic morphology on Middlebrook 7H11 agar is characterized by a very elevated centre surrounded by an uneven flat fringe.
Colony characteristics
Colonies are rough and strongly yellow-pigmented.
Physiology
Slow growth on
Löwenstein-Jensen medium at temperatures between 25 °C and 32 °C within 4 weeks.
Growth at 37 °C is inconsistent and requires longer incubation.
No growth at 42 °C and on MacConkey agar.
The type strain is susceptible in vitro to ciprofloxacin, clarithromycin, rifabutin, rifampicin, sparfloxacin and
The lymph nodes irritation causes a response by the
dust cells/alveolar
macrophages, which cause enzymes, complement proteins, and regulatory factors such as interleukin-1 to get produced.
The
macrophages also carry receptors for lymphokines, and lymphokines act as cytokines which further attract T cells, B cells and natural killer cells. The damage produced by the immune response causes the lung tissue to inflame, expand, and swell with fluid then leak.
Fibrin is then formed in response to the trauma, which is deposited around the wound in the form of a mesh. The fibrin hardens and dries forming a clot that stops leakage of fluid and blood. The
macrophages try to remove the clot and the silica, bu just like asbestos, the silica cannot be digested by any of the breakdown mechanisms of the
macrophages.
Macrophages continue to attempt to remove the foreign substance, and unless the silica is removed by mechanical expulsion means of coughing, the immune response continues.
Continued immune attack by the
macrophages results in silicosis, which repeated relapses making the condition chronic. Exposed people usually remain asymptomatic long after the nodules are apparent on chest
radiography.
Probably an opportunistic pathogen. First isolated from a lymph node of an immunocompromised child and subsequently from tap water and from a respiratory specimen of a patient with chronic fibrosis.