A new rapidly growing mycobacterial species, Mycobacterium murale sp. nov., isolated from the indoor walls of a children's day care centre

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Abstract
Scotochromogenic mycobacterial isolates from water-damaged parts of indoor building materials of a children's day care centre represented a phenetically and genetically distinct group of strains. A 16S rDNA dendrogram (1243 bp) showed that the closest species to the new strain MA112/96Twas Mycobacterium abscessus. Phylogenetic and phenetic analyses (100 characteristics) grouped the new isolates with M. abscessus, Mycobacterium vaccae, Mycobacterium aurum and Mycobacterium austroafricanum. Ribotyping with Pvull restriction distinguished the 5 isolates from the other 12 most closely related species by the major bands at 6·5--7 kb and 13--15 kb. The cell morphology of the new isolates was typical of mycobacteria, electron microscopy revealed a triple-layered cell wall with an irregular electron-dense outer layer. They grew at 10--37 °C with no growth at 45 °C in 5 d. The gene encoding the secreted 32 kDa protein, specific to mycobacteria, was detected by PCR. The main whole-cell fatty acids were characterized by high tuberculostearic acid 10Me-C18:0 (17% at 28 °C), which increased with increasing growth temperature (22% at 37 °C). The other main fatty acids were C18:1 cis9 and C16:0 (21--20% each), followed by, C17:1 cis9 (14%), C16:1 cis10 (8%) and also a high amount of C20 alcohol (9%). α-Mycolic acids, keto-mycolates and wax esters were present (C60-C90), MK-9(H2) (90%) and MK-8(H2) were the main menaquinones. The cellular phospholipids were phosphatidylethanolamine, phosphatidylinositol, phosphatidyl inositolmannosides and diphosphatidylglycerol. Polyamine content was low. G+C content was 72·9 mol%. The new isolates are proposed as a new species, Mycobacterium murale sp. nov. The type strain is MA112/96T(= DSM 44340T).

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