Mycobacterium abscessus


  • 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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Last updated: November 7, 2020