Mycobacteria nontuberculous

Atypical (nontuberculous) mycobacteria Nontuberculous cervical lymphadenopathy (scrofula) occurs in children infected with M. scrofidaceum or M. kansasii. Patients may demonstrate a weakly positive PPD, but diagnosis often requires biopsy. Mycobacterial infections of the skin are usually due to M. marinum. M. avium-intracellulare infects patients with chronic pulmonary disease and may become fulminant in AIDS patients. Atypical mycobacteria are treated with combination chemotherapy or in some cases, surgery. Because drug resistance is more common in nontuberculous mycobacterial infections than in TB, the susceptibility of the infectious agent must be determined early in the course of treatment. 

Hongmanee P., Stender H., Rasmussen O.F. Evaluation of a fluorescence in situ hybridization assay for differentiation between tuberculous and nontuberculous Mycobacterium species in smears of Low-enstein-Jensen and mycobacteria growth indicator tube cultures using peptide nucleic acid probes. J. Clin. Microbiol. 2001 39 1032-1035. 

Anonymous Diagnosis and treatment of disease caused by nontuberculous mycobacteria. Am J Respir Crit Care Med 1997 156 (2 Part 2) S1. 

Interest in the nontuberculous (atypical) mycobacteria, especially members of the Mycobacterium avium, Mycobacterium intracellulare, Mycobacterium scro-fulaceum complex, has also been stimulated by AIDS. Infection with the M. avium complex is seen in up to 50% of patients with AIDS in some areas of the world.3 A review of U.S. cases found an overall 5.5% incidence of M. avium complex in AIDS patients.3 Leprosy, however, is clearly on the wane, although it remains a substantial problem.4 Its prevalence has been steadily diminished to a present-day worldwide figure of about 3 million registered cases and 5.5 million estimated cases, owing in part to a most effective multiple-drug regimen. The World Health Assembly has dedicated itself to the technical elimination of leprosy (that is, a prevalence of less than 1 per 10,000 population) by the turn of the century. 

The standard methods for detection of MTb include acid-fast bacilli (AFB) smear and conventional and liquid culture methods. The AFB smear is rapid, but has a poor sensitivity of 20% to 80%. Another challenge with the AFB smear is that it cannot distinguish MTb from nontuberculous mycobacteria (NTM), such as M. avium-complex (MAC). This distinction is important because disseminated MAC and MTb are both common infections in persons with AIDS. Culture methods for the detection of MTb are sensitive, but growth detectable by standard methods may require 6 to 8 weeks in a culture. Growth often occurs more quickly in liquid culture than with conventional methods, but can still require weeks. With these limitations of culture methods, there was great enthusiasm for nucleic acid testing as a rapid, sensitive method for detection of MTb, especially given the needs to rapidly isolate patients with active, untreated disease and to initiate prompt therapy, particularly in immunocompromised hosts. 

Among the mycobacteria, only M. tuberculosis is a frequent human pathogen. Some nontuberculous mycobacteria (NTM) such as M. kansasii, M. fortuitum, and M. avium complex (MAC) cause... 

These agents are all secondary drugs used only for treatment of disease caused by resistant M. tuberculosis or by nontuberculous mycobacteria. They aU are given parenteraUy and have similar pharmacokinetics and toxicity. Since these agents are potentially ototoxic and nephrotoxic, no two drugs from this group should be used simultaneously, and they should not be combined with streptomycin. 

Clarithromycin and azithromycin are used to treat MAC and other nontuberculous mycobacteria. Clarithromycin alters the metabolism of many other drugs that are metabolized by CYPs, leading to many potential drug interactions. The broader pharmacology of these macrohdes is presented in Chapter 46. 

Clarithromycin is approximately fourfold more active than azithromycin against MAC and is active against most nontuberculous mycobacteria. Azithromycin s lower potency may be compensated for by its greater penetration tissue levels exceed plasma levels by 100-fold. 

IL-12 is an important mediator involved in granuloma formation. Patients with genetic defects in the BL-12/IL-12R system exhibit defective granuloma formation and heightened susceptibility to infections from nontuberculous mycobacteria (110). 

Sood A, Sreedhar R, Kulkami P, et al. Hypersensitivity pneumonitis-like granulomatous lung disease with nontuberculous mycobacteria from exposure to hot water aerosols. Environ Health Perspect 2007 115(2) 262-266. 

Khoor A, Leslie KO, Tazelaar HD, et al. Diffuse pulmonary disease caused by nontuberculous mycobacteria in immunocompetent people (hot tub lung). Am J Clin Pathol 2001 115(5) 755-762. 

Brennan, P.J., M. Heifets, and B.P. Ullom Thin-layer Chromatography of Lipid Antigens as a Means of Identifying Nontuberculous Mycobacteria. J. Clin. Microbiol. 15, 447 (1982). 

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