Microcalorimetric studies of the effects of platinum group metal complexes on bacterial growth

A range of platinum group metal complexes (PGMC) were screened for antibacterial activity against Klebsiella aerogenes and Staphylococcus aureus. The effects of the complexes were monitored by changes in the thermal and growth properties of the organisms. Active complexes caused an immediate cessation of power and biomass production which did not recover whilst the complex was present in the medium. Removal of the complex by washing the cells allowed the growth of the small viable proportion of the cells; the majority of the cells had been killed. Changes which occurred in aqueous solutions of active complexes rendered them less bactericidal; this was a possible cause of regrowth observed at sub-bactericidal levels of some complexes. Resistance to active complexes could not be achieved by serial subculture. Three palladium complexes active against K. aerogenes all had similar square planar structures, but in general it was not possible to correlate activity with structure. The unique effects of the PGMCs at low concentrations, combined with the apparent inability of the bacteria to develop resistance to them, makes the complexes a valuable addition to the antibacterial arsenal.