In the ecology and epidemiologic studies on various serotypes of atypical mycobacteria(AM), Schaefer´s bacterial agglutination test(BA) provided the basis of the serologic procedures. Recently, attempts have been made to modify and to simplify the Schaefer´s BA such as a slide agglutination test(Engel & Beerwald, 197M a "simplified" BA(Reznilov & Leggo, 1972), an agglutination inhibition test(Richards & Eacret, 1972) and "micro method"(Thoen et al., 1975"). The BA, however, was not widely applied as a routine laboratory test mainly because it requires much times and labors to perform and partley because it is not applicable to hydrophobic strains either often encountered in the isolation of AM in the clinical bacteriology or stock strains maintained in the laboratory.
On the contrary, fluorescent antibody technique with mycobacteria may have advantages over the BA because it is far more simpler in serologic procedures and is applicable to all strains of mycobacteria regardless of smooth or rough types of cultures. At the present, it is well known that the type-specific antigens are lacking on the surface of rough type of AM compared to that on smooth type of strain, but the antigenicity on the surface of the hydrophobic strains of AM which resulted from a series of subculture and the strain in the laboratory for 3 to 6 months has not been clarified.
In this study, an attempt to serotype the hydrophobic strains of M. scrofulaceum serotype 41, 42 and 42 by fluorescent anti-complement´ FAC) technique was made. The FAC technique with mycobacteria was also described in detail.
In the summary, the complement firing antibody titres of reference sera to smooth types of homologous serotype was highest, but the antibody titres of reference sera to hydrophobic strains of serotypes, 41, 42 and 43 gave two-to 8-folds lower .that. those to smooth type of strains. Although the sensitivity of type-specific antigens on the hydrophobic strains to reference sera was much lower, using the two units of reference sera determined by titration with hydrophobic strains, three serotypes, i. e., 41, 42 and 43 were specifically differentiated one another by FAC technique.
This result indicated that the hydrophobic strains which were maintained in the laboratory at least for 6 months still retain type-specific antigen detectable by FAC technique.
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