Abstract: The present invention is directed to a microporous filter medium treated with a microbiological interception enhancing agent comprising a cationic chemical having a medium to high charge density and a molecular weight greater than about 5000 Daltons, adsorbed on at least a portion of the microporous structure, and a biologically active metal in direct proximity to the cationic chemical and also on at least a portion of the microporous structure, wherein the flow of fluid through the filter medium decreases in response to an amount of polyanionic acids present in an influent. Robust microbiological interception is still maintained due to the extended empty bed contact time as a result of the diminished flow rate.