Factor Analysis of Saprophytic Serogroups Semaranga and Andamana of Leptospira biflexa

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Abstract
Factor analysis of the saprophytic serogroups Semaranga and Andamana of Leptospira biflexa reveals their main and minor antigens, without deeply affecting their taxonomic status. The analysis shows that in the Semaranga group two subgroups can be recognized on the basis of two main antigens, Sem 2 and Sem 4. The new system for designation of the leptospiral agglutinogens, proposed by Kmety and Lataste-Dorolle, is adopted. The classification of saprophytic leptospiras in serogroups and serotypes is based on the serological tests of microagglutination and ag- glutinin absorption, as suggested by the World Health Organization Group on Leptospirae (14). The classical method of serotyping, in accord- ance with the criterion of Wolff and Broom (13), indicates the 10% limit of the homologous titer in absorbed sera as a measure of differences between two or more serotypes. This criterion, which is successful from an epidemiological and practical point of view, is built on a quantitative basis. A newer criterion, "factor analysis," based on microagglutination and agglutinin absorption tests, has been used for examining "main" and "minor" antigens of pathogenic leptospiras, with the aim of de- fining the antigenic mosaic of each serotype. Main antigens or main antigenic factors are characterized by their ability to elicit the high- est antibody fractions after immunization. From a practical point of view, these antibody fractions should be considered as representing main antigens when a titer of at least five titer stages (or exceptionally l/goo in repeatedly ab- sorbed or in sera from strains with lower im- munogenic potency) is obtained after absorp- tion. Main antigens are considered to be responsi- ble for the homologous titers and co-agglutina- tions of the most closely related strains and elicit antibody responses which are highly re- producible. They determine the serological sta- tus of a strain. Minor antigens are those which have not been found to have the characteristics of main antigens. Consequently, this much wider group of antigens includes those factors which elicit an antibody response at a titer of 1:800 or lower in the absorbed sera. These factors, which have limited importance for clas- sification purposes, are barely detectable by microagglutination and agglutinin absorption tests and are affected by some mutable parame- ters as variability of immune response and different titers in repeated tests (E. Kmety, in press). This arrangement of factor analysis has been codified by E. Kmety in the above-mentioned monograph (in press), although the idea of a deeper study of antigenic composition was sug- gested before by Borg-Petersen (3). Kmety identified a number of factors first in the Australis serogroup (8) and suggested classifi- cation of each new strain by the arrangement of main antigens. Factor analysis of the serotypes belonging to L. biflexa, many of which are agglutinated at a high titer by immune sera directed against mem-

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