Demonstration of Heat‐labile Antigen(s) of Bacteroides Fragilis Associated With Non‐homogeneous Immunofluorescent Staining

Rabbit hyperimmune sera against nine Bacteroides fragilis strains were tested in indirect immunofluorescence against homologous and heterologous formalin and heat-treated bacterial cells. Strain-specific heat-stable and heat-labile antigens were demonstrated as well as many cross-reactive ones. Besides these findings a striking non-homogeneous fluorescence was noted, inasmuch as varying numbers of the bacterial cells were stained while others were not. Results of absorption experiments indicated that the reactive antigens were heat-labile. Non-homogeneous fluorescence was also demonstrated with sera from patients with clinically significant Bacteroides fragilis infections.