Mycobacterium shimoidei, a rare non-tuberculous mycobacteria pathogen identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Abstract

Non-tuberculous mycobacteria (NTM) cause several infectious diseases in humans. This study reports on Mycobacterium shimoidei infection in an immunosuppressed 61-year-old male with a background of emphysema. His chief complaint was haemoptysis. Chest computed tomography showed a large, thin-walled cavitary lesion in the upper right lobe. Although NTM were identified in two separate expectorated sputum samples, DNA–DNA hybridization (DDH) failed to identify the species. M. shimoidei was finally identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Following antimicrobial agent susceptibility tests, treatment with clarithromycin, levofloxacin, and ethambutol commenced. Six months post-treatment, acid-fast sputum culture was negative and repeat imaging demonstrated improvement of the radiographic abnormalities. This study aimed to assess the utility of MALDI-TOF MS for successful identification of rare NTM species that are not identifiable by DDH. It is the first report of M. shimoidei from Okinawa, which is the only prefecture in Japan categorized as subtropical.