• Yoshitaka Tateishi, Yukio Hirayama, Yuriko Ozeki, Yukiko Nishiuchi, Mamiko Yoshimura, Jing Kang, Atsushi Shibata, Kazuto Hirata, Seigo Kitada, Ryoji Maekura, Hisashi Ogura, Kazuo Kobayashi, and Sohkichi Matsumoto.
• Department of Bacteriology, Osaka City University Graduate School of Medicine, and Department of Internal Medicine, National Hospital Organization Toneyama National Hospital, 5-1-1 Toneyama, Toyonaka, Osaka 560-8552, Japan. y-tateishi@med.osaka-cu.ac.jp
• Microb. Pathog. 2009 Jan 1; 46 (1): 6-12.

AbstractMycobacterium avium complex (MAC) disease has been increasing worldwide not only in immunocompromised but also in immunocompetent humans. However, the relationship between mycobacterial strain virulence and disease progression in immunocompetent humans is unclear. In this study, we isolated 6 strains from patients with pulmonary MAC disease. To explore the virulence, we examined the growth in human THP-1 macrophages and pathogenicity in C57BL/6 mice. We found that one strain, designated 198, which was isolated from a patient showing the most progressive disease, persisted in THP-1 cells. In addition, strain 198 grew to a high bacterial load with strong inflammation in mouse lungs and spleens 16 weeks after infection. To our knowledge, strain 198 is the first isolated MAC strain that exhibits hypervirulence consistently for the human patient, human macrophages in vitro, and even for immunocompetent mice. Other strains showed limited survival and weak virulence both in macrophages and in mice, uncorrelated to disease progression in human patients. We demonstrated that there is a hypervirulent clinical MAC strain whose experimental virulence corresponds to the serious disease progression in the patients. The existence of such strain suggests the involvement of bacterial virulence in the pathogenesis of pulmonary MAC disease in immunocompetent status.

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