Bactericidal Activity of Normal Serum Against Bacterial Cultures. I. Activity Against Salmonella typhi Strains

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Abstract
S. typhi (S. typhosa) strains of different antigenic constituents were tested for their resistance to the bactericidal action of normal serum of the guinea pig, rabbit, and human by a quantita-tive growth assay technique. Human serum exerted a greater bacterici-dal effect than guinea pig or rabbit serum, although the order of re-sistance of the strains to serum of the different species was in close agreement. The resistance of the strains containing both O and Vi anti-gens was associated with the O-inagglutinability or Vi content of the organisms. The natural bactericidal antibodies were of marked specificity and directed against either the O or R antigens. The re-sistance of the strains to chloramphenicol or phagocytin did not cor-relate with their resistance to normal serum components. Their re- sistance to the antibiotic was relatively uniform compared to a greater variation in resistance to phagocytin and serum.