STUDIES RELATING TO THE SERUM RESISTANCE OF CERTAIN GRAM-NEGATIVE BACTERIA

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Abstract
Paracolobactrum ballerup, an organism completely insusceptible to the bactericidal action of the antibody-complement system, became extremely sensitive to immune serum and even to normal serum, in conjunction with complement, when cultivated at temperatures above 37[degree]C. This conversion to serum sensitivity was associated with the loss of the organism''s Vi antigen and its tendency to assume a rough state. It did not result in a genetic change in the organism. The loss of serum resistance as a result of cultivation above 37[degree]C may be an indication of the enhancement of host defense mechanisms induced by fever. P. ballerup cultured at 37[degree]C and Salmonella paratyphosa C, organisms considered insusceptible to serum bactericidal action, were not entirely refractory to serum. An absolute distinction between serum-sensitive and serum-resistant gram-negative organisms probably does not exist, but rather there is a very broad distribution of serum sensitivity among these organisms.