Isolation and identification of Mycobacterium avium subspecies silvaticum from a horse

Routine cultivation methods are able to distinguish between isolates of the Mycobacterium avium and the Mycobacterium tuberculosis complex. However, molecular tools are needed to further identify the several subspecies in the M. avium complex, especially for the subspecies avium and silvaticum. A rapid technique using HhaI restriction digestion of a 349 bp amplification product of the 85B antigen (α-antigen) gene was used for the identification of M. avium subsp. silvaticum in a three-year-old gelding presenting with caseous, necrotizing, granulomatous lesions. The result was confirmed by sequencing of the 85B antigen gene.