High virulent clinical isolates of Mycobacterium abscessus from patients with the upper lobe fibrocavitary form of pulmonary disease

Pulmonary disease caused by nontuberculous mycobacteria (NTM), including Mycobacterium abscessus, can be classified into two distinct types of clinical disease; the upper lobe fibrocavitary (UC) form and nodular bronchiectatic (NB) form. However, the relationship between mycobacterial strain virulence and disease type in the pulmonary M. abscessus diseases has not been reported. To determine the differential virulence between strains causing two forms of disease, we obtained clinical isolates from patients with the UC and NB form of pulmonary disease caused by M. abscessus. In present study, we investigated the intracellular growth of clinical isolates in macrophages and their pathogenicity in C57BL/6 mice. For the isolates from the UC form, intracellular macrophage growth was faster and higher levels of cytokines were induced in macrophages than for those from NB form. Moreover, severe lung inflammation was only observed in mice intranasally infected with the isolate from the UC form with the increase of bacterial load. These findings suggest that M. abscessus isolates from the UC form of pulmonary disease are more virulent than those from NB form. This differential virulence of clinical strains may be one of the important factors involved in the determination of the disease form of pulmonary M. abscessus disease.