Peculiar "chestnuts in burrs" formation in MGIT cultures of pulmonary Mycobacterium xenopi cases

We report 3 patients whose sputum and bronchoalveolar lavage fluid (BALF) cultures for acid fast bacteria in MGIT liquid media grew colonies of Mycobacterium xenopi (M. xenopi) with a characteristic chestnut burr like appearance. Patients I, II, and III were a 74-year-old man, 47-year-old woman, and 62-year-old woman, respectively. Chest X ray showed a pulmonary cavity in each case. Patient I had a history of pulmonary and renal tuberculosis. The past medical history of patient II was unremarkable. Patient III had a history of lung cancer. Eight sputum samples and 4 BALF samples from patient I, 3 sputum samples and 1 BALF sample from patient II, and 4 sputum samples from patient III were positive for acid fast bacteria, and the organism was identified as M. xenopi in 9 samples. Smears of these MGIT-positive cultures were stained by the Ziehl Neelsen method, and examined under a microscope. Large and small, spherical shaped, 15-100 microm clusters of thin, elongated bacteria, with a chestnut burr-like or spherical moss like and partly budding appearance, were scattered throughout the smear preparation. Although only 34 cases of M. xenopi infection were reported in Japan between 1984 and 2005, the number of reported cases has been on the increase in recent years. Since no report from Japan, Europe, or the United States have noted the characteristic appearance of M. xenopi in cultures, we consider that the feature described in this communication is useful to presumptively identify M. xenopi.