Clarithromycin-Resistant Nontuberculous Mycobacterial Pulmonary Disease Caused by <i>Mycobacterium florentinum</i> Following <i>Mycobacterium avium</i> Infection: A Case Report

A woman diagnosed with Mycobacterium avium pulmonary disease at age 62 initially received clarithromycin (CAM)-based therapy, which was modified due to adverse effects. Despite treatment, the lesion worsened with hemoptysis, leading to bronchial artery embolization (BAE) and a left upper lobectomy. Treatment was discontinued when clinical stability was achieved after the lobectomy. At 75 years of age, new infiltrates appeared in the residual lung. Treatment was initiated with azithromycin (AZM), sitafloxacin (STFX), and intravenous amikacin (AMK). At 77 years of age, Mycobacterium florentinum was isolated from bronchial washing fluid, and drug susceptibility testing revealed CAM resistance. Despite various regimens, including AZM, moxifloxacin, ethambutol (EB), and AMK, multiple hemoptyses recurred, requiring BAE. The regimen was later rearranged to EB, STFX, AZM, and AMK; however, M. florentinum continued to be isolated in subsequent cultures. M. florentinum is a rare pulmonary mycobacterial pathogen, and reports of CAM-resistant strains are limited. However, this case shows that long-term antibiotic use may result in species replacement from M. avium to M. florentinum, highlighting the need for mycobacterial re-evaluations, especially when a rearrangement of nontuberculous mycobacterial treatment is considered due to a recurrent or refractory disease course. In this regard, bronchoscopy plays a key role in diagnosis.