Genomic Insights Into the Mycobacterium kansasii Complex: An Update

Area of Science:

• Microbiology
• Genomics
• Taxonomy

Background:

• The classification of Mycobacterium kansasii subtypes (I-VI) as distinct species is a recent proposal.
• Previous studies have initiated the reclassification of M. kansasii subtypes into separate species.

Purpose of the Study:

• To computationally validate the species status of former M. kansasii subtypes using extensive genomic data.
• To describe a new species, Mycobacterium ostraviense, replacing former subtype IV.
• To define the Mycobacterium kansasii complex (MKC) encompassing related species.

Main Methods:

• Utilized a three-pronged computational strategy: alignment fraction-average nucleotide identity, genome-to-genome distance, and core-genome phylogeny.
• Analyzed five canonical taxonomic markers: 16S rRNA, hsp65, rpoB, tuf genes, and the 16S-23S rRNA intergenic spacer region (ITS).
• Employed a large and independent sample set for robust phylogenetic and taxonomic analysis.

Main Results:

• Computational analyses strongly supported the elevation of M. kansasii subtypes to distinct species status.
• Confirmed five previously proposed species and described Mycobacterium ostraviense sp. nov. (subtype IV).
• Demonstrated close genetic relatedness and monophyletic origin within the MKC, including Mycobacterium gastri.

Conclusions:

• The Mycobacterium kansasii complex (MKC) is recognized, comprising M. kansasii-derived species and M. gastri.
• Standard taxonomic markers and phenotypic characteristics are insufficient for differentiating MKC species; whole-genome approaches are recommended.
• Rifampicin is a priority treatment for MKC infections, while ethambutol resistance is high.