A SIMPLE CHEMICAL-TEST TO DISTINGUISH MYCOBACTERIA FROM OTHER MYCOLIC-ACID-CONTAINING ACTINOMYCETES

Two hundred and fifty-two representatives of the genera Corynebacteriu m, Gordona, Mycobacterium, Nocardia, Rhodococcus and Tsukamurella were degraded by alkaline hydrolysis and their mycolic acids extracted as methyl esters following phase-transfer-catalysed esterification. When the mycolic acid methyl esters were treated with a mixture of acetonit rile and toluene all mycobacterial mycolates formed copious white prec ipitates whereas all but 5 out of the 106 non-mycobacterial mycolates remained in solution. The precipitated methyl mycolates and the dried soluble mycolates were compared by pyrolysis gas chromatography and si lica gel thin-layer chromatography. On pyrolysis, the precipitated met hyl mycolates from mycobacteria yielded fatty acid methyl esters with 20 to 26 carbon atoms whereas those from the remaining taxa produced s horter-chain esters. Mycobacteria and Tsukamurella paurometabola gave multispot mycotic acid patterns on thin-layer chromatography of their methyl esters whereas those from the remaining strains gave single spo ts. Our results indicate that Rhodococcus chlorophenolicus strains con tain mycolic acids typical of mycobacteria. It can be concluded that t he mycotic acid precipitation test provides a simple and reliable way of distinguishing mycobacteria from all other prokaryotes, notably fro m other mycolic-acid-containing taxa.