Sequence-based differentiation of strains in the Mycobacterium avium complex

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Taxonomy

Background:

• The Mycobacterium avium complex (MAC) comprises several species that are difficult to differentiate using traditional methods.
• Current identification methods like 16S rDNA sequencing lack sufficient discriminatory power for closely related strains within MAC.

Purpose of the Study:

• To evaluate the utility of sequencing the 16S-23S ribosomal DNA (rDNA) internal transcribed spacer (ITS) for differentiating strains within the Mycobacterium avium complex.
• To compare the variability and phylogenetic resolution of ITS sequences with 16S rDNA sequences and serologic typing.

Main Methods:

• Sequencing of the complete 16S-23S rDNA internal transcribed spacer (ITS) region in 35 reference strains of the Mycobacterium avium complex.
• Phylogenetic analysis based on ITS sequences.
• Comparison of ITS sequencing results with 16S rDNA sequencing and DNA-hybridization assays (Gen-Probe).
• Correlation analysis with serologic testing.

Main Results:

• Twelve distinct ITS sequences (sequevars) were identified among the 35 strains.
• ITS sequencing successfully differentiated strains corresponding to Mycobacterium avium and Mycobacterium intracellulare, revealing four and one sequevars, respectively.
• Seven strains exhibited unique ITS sequences, highlighting significant variability within the MAC.
• The 16S-23S rDNA ITS region demonstrated higher variability than the 16S rDNA gene.
• Phylogenetic trees derived from ITS sequences provided more detailed resolution compared to those based on 16S rDNA.
• ITS sequencing results were largely consistent with DNA hybridization but showed poor correlation with serologic typing.

Conclusions:

• The 16S-23S rDNA ITS region is a highly variable and informative marker for differentiating species and strains within the Mycobacterium avium complex.
• ITS sequencing offers superior resolution compared to 16S rDNA sequencing for bacterial identification and strain typing.
• This method has broad applicability for bacterial epidemiology, diagnosis, virulence studies, and taxonomic investigations.