Kinetics of the Bactericidal Action of Normal Serum on Gram-Negative Bacteria

Abstract

The kinetics of the bactericidal action of serum upon Gram-negative organisms was studied with a viable plate count assay. This was found to be a first-order reaction consisting of a definite lag period followed by killing at a constant logarithmic rate. The Q₁₀ of this reaction was about 2. The lag phase probably represents the time required for the formation of intermediate products. The bactericidal reaction was markedly affected by bacterial growth phase. Bacteria in the resting state were resistant to serum, and bacteria in the rapid growth phase were sensitive to serum. In addition, the culture temperature was found to markedly affect the subsequent bactericidal reaction. Bacteria cultured at 37°C were less sensitive to killing at 27°C than those originally cultured at 27°C.