Mycobacterium heckeshornense sp. nov., A new pathogenic slowly growing Mycobacterium sp. Causing cavitary lung disease in an immunocompetent patient

Abstract

A pathogenic scotochromogenic Mycobacterium xenopi-like organism was isolated from the lung of an immunocompetent young woman. This pathogen caused severe bilateral cavitary lung disease, making two surgical interventions necessary after years of chronic disease. This case prompted us to characterize this mycobacterium by a polyphasic taxonomic approach. The isolate contained chemotaxonomic markers which were typical for the genus Mycobacterium, i.e., the meso isomer of 2,6-diaminopimelic acid, arabinose, and galactose as diagnostic whole-cell sugars, MK-9(H(2)) as the principal isoprenoid quinone, a mycolic acid pattern of alpha-mycolates, ketomycolates, and wax ester mycolates, unbranched saturated and unsaturated fatty acids plus a significant amount of tuberculostearic acid, and small amounts of a C(20:0) secondary alcohol. On the basis of its unique 16S rRNA and 16S-23S spacer gene sequences, we propose that the isolate should be assigned to a new species, Mycobacterium heckeshornense. This novel species is phylogenetically closely related to M. xenopi. The type strain of M. heckeshornense is strain S369 (DSM 44428(T)). The GenBank accession number of the 16S rRNA gene of M. heckeshornense is AF174290.

FIG. 1

HPLC mycolic acid patterns of the three M. heckeshornense sp. nov. isolates. IS, internal standards.

FIG. 2

Comparison of 16S rDNA signature sequences (hypervariable regions A and B) of selected species of the genus Mycobacterium including the novel species M. heckeshornense. Dots indicate identity, and hyphens represent alignment gaps. The corresponding positions of the Escherichia coli 16S rDNA are shown for reference. The sequence accession numbers are as follows: M. tuberculosis, X58890; M. avium, X52918; M. celatum, L08170; M. shimoidei, AJ005005; M. nonchromogenicum, X52928; M. triviale, X88924; M. xenopi, M61664; and M. botniense, AJ012756.

FIG. 3

Phylogenetic tree indicating the relationship of M. heckeshornense sp. nov. strain S369^T to other mycobacterial species. The tree was inferred by the neighbor-joining method applied to distances corrected for multiple hits and for unequal transition and transversion rates by Kimura's two-parameter model (10). The tree was routed by using Nocardia asteroides as an outgroup. The bar indicates the expected number of substitutions per site.

FIG. 4

Alignment of 16S-23S rDNA spacer sequences of M. heckeshornense sp. nov., M. xenopi DSM 43995^T (23), and M. botniense ATCC 700701^T (29). Dots indicate identity, and hyphens represent alignment gaps. The lengths of the spacers (in nucleotides) are indicated at the ends of the sequences.