Analysis of cellular fatty acids and proteins by capillary gas chromatography and sodium dodecyl sulphate polyacrylamide gel electrophoresis to differentiate Mycobacterium avium, Mycobacterium intracellulare and Mycobacterium scrofulaceum (MAIS) complex species.

Infections due to atypical mycobacteria have increased during the past 30 years. Species of Mycobacterium avium, Mycobacterium intracellulare and Mycobacterium scrofulaceum are among the most common non-tuberculous mycobacteria isolated from patients with AIDS or immunosuppressed. These three organisms are taxonomically closely related and identification, according to cultural characteristics and biochemical tests, is not always evident, so some of these related strains are grouped in a "MAIS" complex. Analysis of cellular constituents is an aid to identification. Gas chromatography was used to study mycolic acids and a secondary alcohol was found which is a discriminating constituent between M. scrofulaceum and the other two species. The lipidic analysis was not able to separate M. avium and M. intracellulare, so cell proteins were considered. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of proteins reflects genetic relatedness between strains; the different patterns obtained from these three species are described and it is shown that this method is very useful in classification and epidemiology.