Saturday 2 May 2015

Identification of Aerobic Actinomycetes

The nomenclature of the group comprising the branching Gram positive rods is complicated. Considerable morphological diversity is not only seen among genera but also among strains of the same taxon.

Most actinomycetes are typically Gram positive, filamentous, partially acid-fast, branched bacteria that have many microbiological characteristics in common with members of the genera Mycobacterium and Corynebacterium. The major groups of the order Actinomycetales, are actinoplanetes, maduromycetes, nocardioform actinomycetes, and streptomycetes.

Although the aerobic actinomycetes are infrequently encountered in clinical practice, they are important potential causes of serious human and animal infections.

The pathogenic genera within the aerobic actinomycetes are Nocardia, Actinomadura, Streptomyces, Rhodococcus, Gordonia, Tsukamurella and Tropheryma whipplei.

The genus Nocardia currently contains 100 species that have been characterised by phenotypic and molecular methods, and over 30 species are associated with humans. A few of these species have also been recently assigned to other genera. It comprises several species that are known to be unusual causes of a wide spectrum of clinical diseases in both humans and animals. While the majority of nocardial infections have been attributed to Nocardia asteroides, other pathogenic Nocardia species that have been described include Nocardia brasiliensis, Nocardia otitidiscaviarum, and Nocardia transvalensis. In a recent taxonomic revision of the N. asteroides taxon, two new species- N. farcinica and Nocardia nova were separated from it.

For more about the identification of Actinomycetes species, see a special technical note from Public Health England.

 by Tim Sandle

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