Clinical features of patients with bacteraemia caused by Mycobacterium avium complex species and antimicrobial susceptibility of the isolates at a medical centre in Taiwan, 2008-2014

- 30 patients treated for bacteraemia due to Mycobacterium avium complex (MAC) species during 2008-2014 were investigated.
- MAC isolates were identified to species level by rpoB gene and 16S-23S rRNA internal transcribed spacer region sequencing.
- 24 patients had bacteraemia caused by M. avium subsp. hominissuis, 4 by M. colombiense and 2 by M. intracellulare.
- M. colombiense bacteraemia was associated with higher 30-day mortality than M. avium subspecies hominissuis.
- Monitoring susceptibility to ethambutol and fluoroquinolones is warranted in patients with persistent MAC bacteraemia.

Advanced molecular typing methods have greatly expanded the taxonomy of Mycobacterium avium complex (MAC) species; however, little is known about the epidemiology and clinical features of bacteraemia caused by different MAC species. In this study, the clinical characteristics of patients treated for MAC bacteraemia in a tertiary-care centre in northern Taiwan during 2008-2014 were investigated. Isolates were identified to species level by rpoB gene and 16S-23S rRNA internal transcribed spacer region sequencing. Among 30 patients with bacteraemia due to MAC, the majority (n = 26) had concomitant human immunodeficiency virus (HIV) infection. Of the 30 blood isolates obtained from patients, 24 were M. avium subsp. hominissuis, 4 were Mycobacterium colombiense and 2 were Mycobacterium intracellulare. All four M. colombiense isolates were from HIV-infected patients. Bacteraemia due to M. colombiense was associated with higher 30-day mortality than bacteraemia due to M. avium subsp. hominissuis [2/4 (50%) vs. 1/24 (4%); P = 0.045, Fisher's exact test]. All four M. colombiense isolates were susceptible to clarithromycin, moxifloxacin and linezolid. Among the five patients who received ethambutol treatment and four patients who received fluoroquinolone treatment for various durations between positive MAC cultures, two and three patients, respectively, had isolates with significantly increased (≥4-fold) ethambutol and fluoroquinolone minimum inhibitory concentrations. M. colombiense was the second leading causative pathogen of MAC bacteraemia, comprising 15% of all MAC isolates obtained from HIV-positive patients. Monitoring the susceptibility of MAC isolates to ethambutol and fluoroquinolones is warranted in patients with persistent MAC bacteraemia.