Insertion site and distribution of a genomic island conferring DNA phosphorothioation in the Mycobacterium abscessus...

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• Emerging pathogen Mycobacterium abscessus exhibits a DNA degradation (Dnd) phenotype in nearly half of US clinical isolates.
• The Dnd phenotype results from DNA phosphorothioation, a sulfur modification conferred by dnd genes located on mobile elements.

Purpose of the Study:

• To confirm the Dnd-positive status of the M. abscessus type strain ATCC 19977.
• To develop a PCR assay for predicting the Dnd phenotype.
• To investigate the genetic basis and distribution of the Dnd genomic island (GI) within the M. abscessus complex and related species.

Main Methods:

• Pulsed-field gel electrophoresis (PFGE) to assess DNA degradation.
• PCR assay development targeting dndC and the genomic island insertion site.
• Comparative sequence analysis of flanking regions and bioinformatics studies.

Main Results:

• ATCC 19977(T) was confirmed as Dnd-positive.
• A PCR assay successfully differentiated Dnd-positive (dndC amplicon) and Dnd-negative (bridge amplicon) strains.
• The Dnd-GI is 19.6 kbp, flanked by 22 bp repeats, inserted downstream of tRNA-Ala in M. abscessus sensu stricto, and appears to have inserted independently in M. massiliense.
• Dnd-positive clinical isolates were predominantly M. abscessus sensu stricto and belonged to a highly related clonal group.

Conclusions:

• The Dnd phenotype in M. abscessus is linked to a specific, mobile genomic island carrying dnd genes.
• The developed PCR assay is a reliable tool for identifying Dnd-positive strains.
• The Dnd-GI is widespread within M. abscessus sensu stricto, indicating a significant clonal lineage associated with human disease.