Sodium pyrithione and zinc pyrithione (NaPT and ZnPT, respectively) are antimicrobial agents widely used in both the cosmetics and fuel industries. They are also utilized in the mining industry because of their metal chelating properties. They have been shown to depolarize membrane electropotential in fungi and are also known to inhibit fungal and bacterial substrate transport processes. Recent work has shown that both pyrithiones cause the leakage of intracellular material (potassium ions and O.D.260nm absorbing material) from exposed bacterial cells. The work here reports studies on the interactions between the pyrithiones and the bacterial phospholipid head group structures, at both a practical and a theoretical level, utilizing tube dilution neutralizer studies, scanning spectrophotometry and molecular modelling. The tube dilution neutralizer studies exhibited a decrease in minimum inhibitory concentration (MIC) for both pyrithiones in the presence of extracellular phosphatidyl‐ethanolamine and EDTA. Scanning spectrophotometry exhibited the chelation of the central zinc atom from the ZnPT chelate by the addition of EDTA. Molecular modelling studies exhibited the chelation of the phosphatidyl‐ethanolamine head group by ZnPT. Zinc pyrithione also exhibited an interaction with the ammonium tail of the head group structures. Sodium pyrithione exhibited electrostatic interactions with the phospholipid head groups in the molecular modelling studies.

Many antimicrobial compounds exhibit bacterial cell membrane activity as either potassium ion leakage and/or leakage of material that absorbs at 260 nm from the cell. In this experiment a potassium ion selective electrode and spectophotometric observation of 260-nm leakage were used in order to examine cell membrane effects in a selection of common biocides upon both Escherichia coli NCIMB 10000 and Pseudomonas aeruginosa NCIMB 10548. The observation of potassium ion leakage for pyrithione biocides yielded results which were initially difficult to interpret, but are thought to suggest a species-dependent combination of potassium ion leakage from affected membranes and chelation of those leaked ions in the bathing suspension. Such a result is not, however, supported by the 260-nm material leakage results, which indicate very similar levels of membrane active effects for both species of bacteria.