Partially Acid-Fast Aerobic Actinomycetes

 Nocardia spp.

 Nocardia organisms are normal inhabitants of soil and water and are primarily responsible for the decomposition of plant material. Infections caused by Nocardia spp. are found worldwide. Because they are ubiquitous, isolation of these organisms from clinical specimens does not always indicate infection. Rather, isolation may indicate colonization of the skin and upper respiratory tract or laboratory contamination, although the latter is rare. Nocardia infections can be acquired either by traumatic inoculation or inhalation. N. asteroides sensu stricto type VI is evenly distributed throughout the United States, as is N. farcinica. The prevalence of other species varies region ally; N. brasiliensis is associated with tropical climates and has a higher prevalence in the southwestern and south eastern United States.

Nocardia spp., particularly N. asteroides, are facultative intracellular pathogens capable of growth in various human cells. The mechanisms of pathogenesis are complex and not completely understood. However, the virulence of N. asteroides appears to be associated with several factors, such as stage of growth at the time of infection, resistance to intracellular killing, tropism for neuronal tissue, and ability to inhibit phagosome lysosome fusion; other characteristics, such as production of large amounts of catalase and hemolysins, may also be associated with virulence.

Rhodococcus, Gordonia, Tsukamurella spp. Rhodococcus, Gordonia, and Tsukamurella spp.

can be isolated from several environmental sources, especially soil and farm animals, as well as from fresh water and salt water. The organisms are believed to be acquired primarily by inhalation. For the most part, these aerobic actinomycetes are infrequently isolated from clinical specimens.

To date, Rhodococcus equi has been the organism most commonly associated with human disease, particularly in immunocompromised patients, such as those infected with the human immunodeficiency virus (HIV). R. equi is a facultative intracellular organism that can persist and replicate within macrophages. Determinants of the virulence of R. equi are under investigation and may involve cell wall mycolic acids that may play a role in intracellular survival, production of interleukin-4, and granuloma formation. Although Gordonia spp. and Tsukamurella are able to cause opportunistic infections in humans, little is known about their pathogenic mechanisms.

 Non–Acid-Fast Aerobic Actinomycetes: Streptomyces, Actinomadura, Dermatophillus, Nocardiopsis, and the Thermophilic Actinomycetes

 Aspects of the epidemiology of the non–acid-fast aerobic actinomycetes are summarized in Table 1. Little is known about how these agents cause infection.

Table1. Epidemiology of the Non–Acid-Fast Aerobic Actinomycetes

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مواضيع ذات صلة

Laboratory Diagnosis for Nocardia, Streptomyces, Rhodococcus, and Similar Organisms

General Characteristics of Nocardia, Streptomyces, Rhodococcus, and Similar Organisms

Pathogenesis of Streptococcus pneumoniae

Treatment and Prevention of Staphylococcus aureus

Pathogenesis of Staphylococcus aureus

Direct Detection Methods for Erysipelothrix, Lactobacillus, and Similar Organisms

Pathogenesis and Spectrum of Disease Erysipelothrix, Lactobacillus, and Similar Organisms

Antimicrobial Susceptibility Testing and Therapy for Listeria, Corynebacterium, and Similar Organisms

Approach to Identification for Listeria, Corynebacterium, and Similar Organisms

GROWTH AND METABOLISM

SPORES AND SPORULATION

Susceptibility Testing