Gold, platinum, and palladium ions demonstrate strong antimicrobial action against hospital pathogens with reduced effect in the presence of bovine plasma soil

AIMS: The antimicrobial efficacy of five metal ions (silver, copper, platinum, gold, and palladium) was assessed against Klebsiella pneumoniae, Acinetobacter baumannii, and Enterococcus faecium in the presence and absence of a bovine plasma soil. Changes in the elemental structure of the bacteria were identified. METHODS: Planktonic and biofilm inhibition assays were carried out in the absence and presence of a 10% bovine plasma soil. Elemental changes to the bacteria were determined using energy-dispersive X-ray spectroscopy (EDX). RESULTS: The reduction in planktonic bacteria without soil was 8-log at 0 h for gold and palladium ions, and with soil, platinum demonstrated a 7-log reduction at 4 h against K. pneumoniae and A. baumannii. For E. faecium with and without soil, a 4-log reduction at 24 h with silver ions was demonstrated. Reduction of biofilm without soil was 88.8% against K. pneumoniae (platinum) 91.2% (gold) against A. baumannii, and 82.3%-82.9% (platinum/palladium/gold) against E. faecium. With soil, biofilm reduction for K. pneumoniae or A. baumannii with gold ions was 82.3%, and with gold ions against E. faecium 25.5%. Elemental changes following metal ion treatment could be indicative of cellular damage but did not always correlate with the antimicrobial activity. In the presence of the soil, a decrease in the antimicrobial efficacies was demonstrated, and fewer elemental changes were detected. CONCLUSIONS: Platinum, palladium, and gold ions were the most effective antimicrobials. Across all three tested genera, soils reduced the antimicrobial activity.