Iron compounds and resistance to infection. Further experiments with Clostridium welchii type A in vivo and in vitro.

Transferrin has a bacteriostatic effect on Clostridium welchii type A provided it is stabilized by the presence of serum albumin. However, the bacteriostatic properties of whole serum cannot be attributed entirely to transferrin since it has been found that a mixture of transferrin and β2- or γ-globulin is required to imitate exactly the behaviour of whole serum. Fe3+, haematin, and haemoglobin abolish bacteriostasis in vitro, but large amounts of Cl. welchii α-antitoxin or Cl. tetani antitoxin tend to inhibit bacterial growth in the presence of excess Fe3+ when the environment is maintained at a high Eh (+110 mV, pH 7.5). A number of factors have been shown to influence the outcome of Cl. welchii infections in guinea-pigs given intravenous Fe3+ (5 mg/kg). In the case of limb infections, 1300 units of α-antitoxin protected animals receiving 105 bacteria but failed to protect animals receiving 107 bacteria; 1300 units of α-antitoxin failed to protect animals injected with 105 bacteria in the lumbar region. The limb lesion has been found to contain an Eh gradient rising from –400 mV at its centre to +300 mV in normal tissue. Changes in the size of the area of low Eh can be correlated with the outcome of the infection. The results of these experiments provide some indication of the factors that are likely to influence the outcome of Cl. welchii infections.