Mycobacterium abscessus
Paul Auwaerter, M.D.
MICROBIOLOGY
MICROBIOLOGY
MICROBIOLOGY
- Human mycobacterial pathogen, occasional environmental contaminant. Present in water, sewerage, vegetation.
- Considered among the most pathogenic and chemotherapy-resistant of rapid-growing Mycobacteria.
- The organism produces clavulanate-insensitive broad-spectrum β-lactamase that limits the in vivo efficacy of β-lactams[10].
- Culture on both solid and liquid media preferred to increase sensitivity.
- CLSI recommends 7H10 and 7H11 solid media at 36°C for slow growers (and 28°C for rapid growers).
- Some use Löwenstein-Jensen slants as the most sensitive media.
- Typically, respiratory specimens treated with 0.25% N-Acetyl-L-cysteine and 1% NaOH for decontamination.
- As a reminder,
- Mycobacteria spp. divided into rapid growers (< 7 days) and slow growers (>7 days) based on time to mature growth on agar plates.
- Rapid growers (often 3-7d): M. abscessus, also M. fortuitum: (3-7 days), M. chelonae.
- Slow growers (> 7-10d): M. gordonae(7-10 days), M. malmoense, M. marinum; M. ulceransandM. xenopi(3-8 wks in Cx), M. terrae, M. nonchromogenicum, (also:M. kansasii, M. avium-intracellulare, M. tuberculosis)
- Formerly part of "M. chelonae-complex", but important to distinguish from M. chelonae as antimycobacterial therapy more difficult with M. abscessus senso strictu.
- Three human subspecies have been proposed: molecular identification (e.g., hsp65 or rpoB gene-based typing necessary to distinguish) recommended; usual biochemical/phenotypic methods fail. Speciation is difficult and there is not uniformity in recognition, so confusion is not infrequent when applying labels to M. abscessus isolates.
- M. abscessus subsp. abscessus
- Seen more commonly in North America
- Many isolates have mutational resistance or inducible resistance re: function erm gene.
- Resistance often is seen after the 3-14d employment of macrolide.
- Testing of isolates for inducible macrolide resistance suggested.
- Prior exposure to macrolides heightens the likelihood of macrolide resistance.
- ~20% of M. abscessus subsp abscessus isolates contain an inactive erm gene.
- If so, this translates into an improved chance of success the chances of a successful treatment outcome with macrolide-based therapy
- M. abscessus subsp. massiliense
- Lacks inducible macrolide resistance or erm gene[15](non-functional)
- More frequently seen in Korea.
- M. abscessus subsp. bolletii°
- May have an inducible erm gene.
- The first two species 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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