The role of Eh, pH and iron in the bactericidal power of human plasma

The bactericidal power of fresh human plasma against Klebsiella pneumoniae and Escherichia coli was extremely sensitive to changes in Eh and pH. At a high Eh (approx. + 200 mV) the bacteria were destroyed, but rapid regrowth occurred when the Eh was lowered to approx. −400 mV. Abolition of the bactericidal effect was also produced by adding ferric iron at a high Eh (approx. + 200 mV). Lowering the pH to 6.50 reduced or prevented the bactericidal effect. These results are probably related to the availability of iron for bacterial growth, and could be important for understanding the development of infection in injured or diseased tissue.