**7. Activity of Delpazolid on Nontuberculous Mycobacteria**

Nontuberculous mycobacteria (NTM) are naturally occurring organisms found in water and soil. They are associated with biofilm formation, which enhances their disinfectant and antibiotic resistance. Particularly, *Mycobacterium avium* complex and *Mycobacterium abscessus* are the most common causes of pulmonary NTM and deadly pathogens, with high failure rates and relapse rates that may exceed 40% [20]. Although most people are not affected by such pathogens, in some individuals susceptible to conditions such as cystic fibrosis, chronic obstructive lung disease, bronchiectasis, and thoracic skeletal abnormalities, progressive and debilitating disease can occur [21].

A key concern in NTM treatment is the lack of antibiotics appropriate for long-term treatment for diverse NTM pathogens. Here, we evaluated the activity of delpazolid via in vitro susceptibility tests, as shown in the table below (Table 7) [22].


**Table 7.** MICs of antibiotics against clinical isolates of NTMs.

Delpazolid had MICs similar to those of linezolid against *M. avium*, *M. abscessus*, *M. fortuitum*, *M. kansasii*, and *M. chelonae*, and inhibited NTM proliferation. In particular, delpazolid was effective against several *M. abscessus* strains in vitro and in a macrophage infection model. Acute infections in C57BL/6 mice, delpazolid 100 mg/kg exhibited greater in vivo efficacy than clarithromycin 200 mg/kg, a macrolide that is the main drug currently for *M. abscessus* treatment [12]. Therefore, delpazolid represents a promising novel class of oxazolidinones with improved safety for the treatment of *M. abscessus*.
