Tuberc Respir Dis.
2005 Jul;59(1):39-46.
Clinical Significance of Low-colony Count Scotochromogen Nontuberculous Mycobacteria
- Affiliations
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- 1Division of Pulmonary and Critical Care Medicine, University of Ulsan College of Medicine, Asan Medical Center, Korea. shimts@amc.seoul.kr
- 2Department of Diagnostic Laboratory Medicine, University of Ulsan College of Medicine, Asan Medical Center, Korea.
- 3Asan Institute for Life Sciences University of Ulsan College of Medicine, Asan Medical Center, Korea.
- 4Department of Biomedical Laboratory Science, Yonsei University Wonju College of Medicine, Korea.
- 5Product Planning and Development Department M&D Co., LTD4, Korea.
Abstract
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BACKGROUND: Even though it has been suggested that low-colony, scotochromogen nontuberculous mycobacteria (NTM) are usually contaminants and not true pathogens, evidence for this hypothesis has not been provided. This study investigated the colony characteristics, organism identification, and clinical significance of low-colony scotochromogen.
METHODS
The laboratory cultured 6,898 respiratory clinical specimens for an examination of mycobacteria over a three-month period. A low-colony count was arbitrarily defined as < or = 20 colonies. This study analyzed the recovery rate of the mycobacteria, the number of colonies and their gross characteristics, and their clinical significance. PCR- restriction fragment length polymorphism analysis was carried out to identify the NTM species. NTM pulmonary disease was defined according to the American Thoracic Society.
RESULTS
A total of 6,898 respiratory specimens for mycobacterium were cultured. Of these, 263 (3.8%) grew NTM, and 382 (5.5%) grew M. tuberculosis. Of the 263 cultured NTM specimens, 124 (47.1%) were scotochromogens. The smear-positive rate was significantly lower in these scotochromogens (4.8%) than in the non-scotochromogens (23.7%) (p<0.05). The most common isolates were M. gordonae (83/102, 81.4%) in the scotochromogens, and MAC (52/121, 43.0%) in the non-scotochromogens. Even though three out of 113 patients with a low-colony scotochromogen has been diagnosed with NTM pulmonary disease, the isolated scotochromogen was not considered to be the cause of the NTM disease but was just a contaminant.
CONCLUSION
In this study, the most common isolate of a low-colony count scotochromogen was M. gordonae, which appeared to be contaminants and not true pathogens. Greater efforts in the quality control of a mycobacterium laboratory are needed in cases where there is a high recovery rate of low-colony count scotochromogen.
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