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

Abstract

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.

Natural resistance, iron and infection: a challenge for clinical medicine

“…The bactericidal effect was restored by introducing air into the system and raising the Eh from approximately 2400 to +200 mV. This shows that exposure to a low Eh does not permanently damage the bactericidal system and that bacterial killing can be switched on or off simply by adjusting the Eh (Bullen et al, 1992). The same applies to the pH of the system whereby the binding of iron by transferrin is progressively lost as the pH and the concentration of bicarbonate ion both fall (Lestas, 1976;Evans et al, 1999).…”

False‐positive alarms for bacterial screening of platelet concentrates with BacT/ALERT new‐generation plastic bottles: a multicenter pilot study

“…The specific measures taken to minimize this risk of an artificial contamination during the inoculation of the first culture limit the probability of this explanation for such a result. It is much more likely that bactericidal effects of plasma 17 account for the difficulties to confirm the initially positive signal. This may be especially relevant for very low levels of bacterial contamination and for slowly growing organisms 18 .…”

Iron and infection: the heart of the matter

“…Small numbers of E. coli grew rapidly in normal human plasma at an Eh of about −400 mV, pH 7.5. When the Eh was raised to about +200 mV, pH 7.5 by introducing air into the system rapid killing started within 2 h. The ability to restore the bactericidal effect is significant because it shows that a low Eh does not irreversibly damage the bactericidal system [30]. The pH of tissue fluids is equally important because the binding of iron by transferrin is progressively lost at a pH of 6.7 or below, and this is accompanied by the loss of bactericidal effects against many different organisms [28,30].…”