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- Human pathogen, occasional environmental contaminant. Present in water, sewerage, vegetation.
- Considered among the most pathogenic and chemotherapy-resistant of rapid-growing mycobacteria.
- Organism produces clavulanate-insensitive broad-spectrum β-lactamase that limits the in vivo efficacy of β-lactams.
- Formerly part of "M. chelonae-complex", but important to distinguish from M. echelon as antimycobacterial therapy more difficult with M. abscessus senso strictu.
- Three human subspecies have been proposed: rpoB gene-based typing necessary to distinguish; usual biochemical/phenotypic methods fail. Speciation is difficult and there is not uniformity in recognition, so confusion in not infrequent when applying labels to M. abscessus isolates.
- M. abscessus subsp. abscessus
- Seen more commonly in North America
- Many isolates have the erm gene, which confers macrolide, often inducible, resistance.
- Resistance often seen after 3-14d employment of macrolide. Testing of isolates for inducible macrolide resistance suggested.
- M. abscessus subsp. massiliense
- Lacks inducible macrolide resistance or erm gene.
- More frequently seen in Korea.
- M. abscessus subsp. bolletii
- First two represent most human infections.
- Occasionally confused with Corynebacterium spp. (described as diphtheroid growing in broth systems).
- In vitro resistance rates (most studies from Asia):
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