Abstract
Antisera were prepared against [rabbit] M. morganii (P. morganii) type strains. The specificities of the somatic (O) antigens were studied using the passive hemagglutination and slide agglutination techniques. Previously unreported interstrain relations were observed and O groups were provisionally defined on the basis of related strains. Of 143 isolates, collected mostly from 2 hospitals, 96% could be placed in 1 or another of the O groups and 48% belonged to O group 1 and most of these were of 2 serotypes, Olab, 2 (20%) and Olad, 2 (12%).