Media exchange method for demonstrating killing of L-phase variants in solid media by normal human serum

Normal human serum has been shown to kill L-phase variants in a fluid system by the action of antibody plus complement. Previous studies, however, failed to demonstrate such killing in solid media. This failure probably resulted from inhibition of complement by medium components such as agar and NaCl. A method was developed which circumvents the problems of the anticomplementary properties of agar media and the requirement of some L-phase variants for concentrations of salt that inhibit complement. Using this method, we have demonstrated in solid media the killing by normal human serum of the L-phase variants of Staphylococcus aureus, Proteus mirabilis, Streptococcus pyogenes, S. faecalis, Pseudomonas aeruginosa, and Salmonella typhi. This method provides a relatively simple and graphic means for studying host humoral factors lethal for L-phase variants.