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Environmental Analysis

Thermophilic actinomycetes [C226]

Published: July 8th, 2009

Revised: October 4th, 2009

This test determines the presence of culturable thermophilic actinomycetes in bulk and swab samples. Test results are provided semiquantitatively as 1+, 2+. 3+, etc., where the number preceding the “plus sign” indicates the order of magnitude of colonies observed.

Actinomycetes are a large and diverse group of Gram-positive bacteria that have growth habits similar to fungi in that they produce branching networks of filaments. Thermophilic actinomycetes occur in a wide range of habitats including common materials such as self-heating plant matter and manure composts. They are also known from highly specialized habitats such as birds’ nests, volcanic vents and hot springs. The term thermophilic refers to the fact that the actinomycetes in question grow optimally at temperatures above 40 °C. Other groups of actinomycetes are known to occur at moderate or extreme cold temperatures.

Actinomycetes are notable as prolific producers of microbial volatile organic compounds (mVOCs). Indeed in this regard, they tend to be much more active than most fungi. Some of the mVOCs commonly produced by actinomycetes are responsible largely for the mouldy or musty odours associated with soils as well as damp basements. Actinomycetes are also extremely active producers of antimicrobial chemicals. Many of the naturally produced antimicrobial drugs in common use today are derived from actinomycetes (e.g. streptomycin, nystatin, and tetracycline). Inhalation exposure to cells and other materials colonized by actinomycetes has been associated with respiratory diseases such as hypersensitivity pneumonitis. This is particularly evident in agricultural settings where actinomycete exposures are known to play a role in the disease known as Farmer’s Lung.

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