IODINATION OF BACTERIA - A BACTERICIDAL MECHANISM

Myeloperoxidase, iodide and H2O2 have a bactericidal effect on Escherichia coli. Myeloperoxidase can be replaced by lactoperoxidase or a guinea pig leukocyte particulate preparation, H2O2 by a H2O2 generating system and iodide by thyroxine, triiodothyronine or by other halides (bromide, chloride). The bactericidal effect high at pH 5.0 decreased as the pH was increased. The antibacterial effect is not primarily due to the I formed by iodide oxidation. The bacteria must be present in the reaction mixture during the process of iodide oxidation suggesting the involvement of more labile intermediates of iodide oxidation. Iodination of the bacteria by the meloperoxidase-iodide-H2O2 system was demonstrated chemically and radioautographically. There was a close correspondence between the bactericidal effect and the iodination of the bacteria in all the parameters measured. The iodination reaction occurs in the intact neutrophilic polymorphonuclear leukocyte after phagocytosis of bacteria since the iodination may result from the operation of the myeloperoxi-dase-iodide-H2O2 system. The leukocyte peroxidase, myeloperoxidase, may form an antibacterial system when combined with an oxidizable substance such as iodide (or chloride) ion and H2O2 formed by leukocyte or microbial metabolism.