Demonstration by Fluorescence Microscopy of Adsorption onto Bacteria of a Heat-Labile Factor from Guinea Pig Serum

Abstract

Immunofluorescent techniques have been utilized to study adsorption of heat-labile serum components and of antibody onto bacteria. On incubation of staphylococci or salmonellae with fresh guinea pig serum, a heat-labile factor was adsorbed onto the bacteria. This adsorption did not take place at 0°C, and was also blocked by high salt concentrations in the medium. Divalent cations were not required for adsorption. Heat-labile guinea pig serum factor bound to the bacterial surface was altered or destroyed on exposure to 56°C, to trypsin or to hydrazine. Incubation of fresh guinea pig serum with concentrated suspensions of Staphylococcus albus, followed by removal of the microbes by centrifugation, led to reduction or elimination of the content of heat-labile factor as estimated by immunofluorescence tests employing the homologous staphylococcus or an unrelated organism, Salmonella typhimurium. Fluorescence techniques were devised that permitted estimation of adsorption to the same bacterial cells of both heat-labile serum factor and specific antibody. Adsorption to staphylococci of either of these two serum components did not detectably augment or diminish subsequent binding of the other.