Rapidly Growing Nontuberculous mycobacteria (RGM)
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p491-493
2025-09-02
350
Mycobacteria that produce colonies on solid media in 7 days or earlier constitute the second major group of NTM. Currently, approximately 70 species have been classified into this group.
General Characteristics
The large group of organisms that constitute the RGM is divided into six major groups of potentially pathogenic species, based on pigmentation and molecular studies. Unlike the majority of other mycobacteria, most rapid-growers can grow on routine bacteriologic media and on media specific for cultivation of mycobacteria. On Gram staining, these organisms appear as weakly gram-positive rods resembling diphtheroids.
Epidemiology and Pathogenesis
The rapidly growing mycobacteria considered potentially pathogenic can cause disease in either healthy or immunocompromised patients. Like many other NTM, these organisms are ubiquitous in the environment and are present worldwide. They have been found in soil, marshes, rivers, and municipal water supplies (tap water) and in marine and terrestrial life forms. Infections caused by rapidly growing mycobacteria can be acquired in the community from environmental sources. They also can be nosocomial infections, resulting from medical interventions (including bone marrow transplantation), wound infections, and catheter sepsis. These organisms may be commensals on the skin. They gain entry into the host by inoculation into the skin and subcutaneous tissues as a result of trauma, injections, or surgery, or through animal contact.
The RGM also can cause disseminated cutaneous infections. The description of chronic pulmonary infections caused by rapidly growing mycobacteria suggests a possible respiratory route for acquisition of organisms present in the environment. Of the potentially pathogenic, rapidly growing NTM, M. fortuitum, M. chelonae, and M. abscessus are commonly encountered; these three species account for approximately 90% of clinical disease. Little is known about the pathogenesis of these organisms.
Spectrum of Disease
The spectrum of disease caused by the most commonly encountered rapid-growers is summarized in Table 1. The most common infection associated with RGM is post traumatic wound infection. An increase in wound infections has been associated with planktonic M. abscessus, which can be identified as a rough colonial phenotype on artificial media; these organisms are capable of infecting macrophages. The smooth colonial phenotype typically is identified in biofilms and lacks infectivity.
Table1. Common Types of Infections Caused by Rapidly Growing Mycobacteria
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