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In contrast to the growth of fungi, the growth of mycobacteria in moisture-damaged building materials has rarely been studied. Environmental mycobacteria were isolated from 23% of samples of moisture-damaged materials (n ‫؍‬ 88). The occurrence of mycobacteria increased with increasing concentrations of fungi. Mycobacteria may contribute to indoor exposure and associated adverse health effects.

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A yellow-pigmented, scotochromogenic, slowly growing mycobacterial strain, designated T1921 T , was isolated from the disseminated osteomyelitic lesions of a 7-year-old child with an underlying partial gamma interferon receptor alpha-1 deficiency. Hybridization by the line probe assay indicated the presence of a Mycobacterium species. Sequencing of the 16S rRNA gene, the internally transcribed spacer (ITS) region and the hsp65 and rpoB genes revealed that strain T1921 T could be differentiated from all recognized species of the genus Mycobacterium. Phylogenetic analysis based on the 16S rRNA gene indicated that strain T1921 T was related most closely to Mycobacterium intracellulare, whereas analysis based on the ITS and hsp65 and rpoB genes indicated that it was most closely related to Mycobacterium avium. Phenotypic tests were not able to differentiate strain T1921 T from similar slowly growing mycobacteria. Strain T1921 T is considered to represent a novel species of the genus Mycobacterium, for which the name Mycobacterium arosiense sp. nov. is proposed. The type strain is T1921 T (5DSM 45069 T 5ATCC BAA-1401 T ).

Cellular fatty acid analysis by GLC is widely used in the species identification of mycobacteria. Combining mycolic acid cleavage products with shorter cellular fatty acids increases the informative value of the analysis. A key has been created to aid in the identification of all currently known slowly growing environmental species. In this scheme, the species are classified into six categories, each characterized by a combination of fatty markers shared by those species. Within each category, individual species may be distinguished by the presence or absence of specific marker substances, such as methyl-branched fatty acids or secondary alcohols. This study also describes earlier unpublished GLC profiles of 14 rare, slowly growing, environmental mycobacteria, Mycobacterium asiaticum, Mycobacterium botniense, Mycobacterium branderi, Mycobacterium conspicuum, Mycobacterium cookii, Mycobacterium doricum, Mycobacterium heckeshornense, Mycobacterium heidelbergense, Mycobacterium hiberniae, Mycobacterium kubicae, Mycobacterium lentiflavum, Mycobacterium scrofulaceum, Mycobacterium triplex and Mycobacterium tusciae. Though no single identification technique alone, even sequencing of an entire single gene such as 16S rRNA, can identify all mycobacterial species accurately, GLC has proven to be both reliable and reproducible in the identification of slowly growing mycobacteria. In cases of earlier unknown species, it generates useful information that allows their further classification and may lead to the description of novel species.