Studies on the classification of the Klebsiella 1

Cross precipitin reactions of 72 type sera of the Klebsiella group prepared by immunizing rabbits with living organisms were studied. The saline suspensions of organisms grown on an agar medium were heated at 100°C. for 1 hour, centrifuged, and the supernatants were used as type antigens. With a few exceptions, homologous precipitin reactions were easily distinguished from heterologous ones, since the formers tended to occur more rapidly and intensely than the latters, showing higher antigen and antibody titers. However, there were a few antigens which showed weak cross reactions but high antigen titers, probably due to the reactions with K antigens. Moreover, antigens showing weak and retarded cross reactions and very low antigen titers seemed to react with many type sera, probably due to the reactions with O antigen which contained within type antigens.