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.