The effects of some platinum group metal complexes on bacterial growth

Abstract

Experimental conditions were established which gave reproducible power-time and biomass-time traces for Klebsiella aerogenes growing in glucose-limited medium and Staphylococcus aureus 13137, Ps47 and Pseudomonas aeruginosa in nutrient broth. Aeration of the cultures was critical in determining the shape and reproducibility of the power-time traces. High oxygen tensions caused a reduction in the final biomass value and an increase in waste heat production in nutrient broth. Biomass production occured without any accompanying heat production and vice versa in nutrient broth. The reproducible power-time and biomass-time traces were used to assess the effects of a range of platinum group metal complexes (PGMC) on bacterial metabolism. Several complexes showed anitbacterial activity unlike any other antibacterial agent studied, whilst other complexes had a negligible effect on bacterial growth. Generally complexes were active against either K.aerogenes or S.aureus. Neither organism was able to develop resistance against active complexes. No structure-activity relationships could be established. However, three square-planar palladium complexes, with different ligands, had similar effects on the thermal and growth properties of K.aerogenes. Changes occurring in PGMC solutions with time, monitored spectrophotometrically, reduced antibacterial activity as did interactions between the complex and components of nutrient broth. PGMC solutions had a markedly different effect on bacterial growth when present in the medium before inoculation compared to the effect when the complex was injected in the mid-exponential growth phase. Microcalorimetry is a technique which allows for rapid screening of complexes and continuous monitoring of their effects on bacterial metabolism. The apparent inability of bacteria, even a strain of S.aureus resistant to several antibiotics, to develop resistance against active complexes indicates their potential in clinical applications.