Histologic and genotypic characterization of a novel Mycobacterium species found in three cats

Abstract

Three cases of feline atypical mycobacteriosis from different geographical regions in North America were characterized by large clusters of filamentous bacteria visible on hematoxylin-and-eosin-stained tissue sections. PCR amplification demonstrated the presence of Mycobacterium-specific nucleic acid in samples of skin lesions from these cases. PCR-assisted cloning and DNA sequence analysis of a 541-bp length of the Mycobacterium 16S rRNA gene generated DNA sequences which were >95% identical, suggesting that the three isolates were closely related. Two of the sequences were 99% identical and may represent the same species. Alignment with comparable 16S rRNA gene sequences from 66 Mycobacterium species and partially characterized isolates highlighted similarities (>94%) with Mycobacterium bohemicum, Mycobacterium haemophilum, Mycobacterium ulcerans, Mycobacterium avium subsp. avium, and isolate IWGMT 90242. Parsimony analysis of sequence data suggested relatedness to M. leprae. Significant molecular genetic and pathobiological differences between these three similar isolates and other known species of mycobacteria suggested that the organisms may not have been described previously and that these cases may represent a new form of mycobacterial disease in cats. We suggest the term "Mycobacterium visibilis" to describe the organism from which the two nearly identical sequences were obtained.

FIG. 1.

Photograph of heart and lung of cat 1. White 1- to 2-mm-diameter foci (small arrows) are visible on the epicardial surface.

FIG. 2.

Photomicrograph of dermis of cat 1 showing numerous thin, filamentous bacteria within a lipid-like vacuole, surrounded by large macrophages. Hematoxylin and eosin stain was used. Magnification, ×250. Bar, 50 μm.

FIG. 3.

Phylogenetic relationships based on approximately 550 bases of the 16S rRNA genes of selected mycobacteria and Mbv1, Mbv2, and Mbv3 sequences, calculated by the maximum-likelihood method.

FIG. 4.

Sequence alignment for a portion of the 16S rRNA gene from selected mycobacteria, showing sequence similarity between M. leprae and Mbv1, Mbv2, and Mbv3 at variable region 1. Boxed bases are different from the consensus sequence.