Sensitization of complement-resistant smooth gram-negative bacterial strains.

Many gram-negative bacteria are susceptible to the bactericidal action of complement in the presence of specific antibody. As a general rule, rough strains are readily killed, whereas smooth strains are relatively resistant. The results of this study show that the serum sensitivity of smooth gram-negative organisms can be controlled by the environmental conditions imposed by the test system. Smooth organisms which are completely resistant to the bactericidal action of immune serum plus complement in the presence of divalent cations become quite sensitive in a test system containing a relatively high concentration of certain univalent cations; this effect is potentiated by ethylenediaminetetraacetic acid. Since it is generally accepted that the serum resistance of smooth gram-negative organisms is associated with the protection afforded by their thick lipopolysaccharide layer, it is suggested that environmental conditions favoring serum sensitization cause some structural disorganization of the smooth lipopolysaccharide of these cells.