Table 3.

Fractional inhibitory concentration index for metal ion combinations demonstrating a synergistic antimicrobial efficacy for silver/copper against K. pneumoniae and silver/palladium against E. faecium.

Metal ion combinations	AgCu	AgPt	AgAu	AgPd	CuPt	CuAu	CuPd	AuPt	AuPd	Ptpd
K. pneumoniae	0.57 ± 0	0.66 ± 0	0.73 ± 0.68	0.73 ± 0.68	0.92 ± 0.68	0.67 ± 0.68	0.90 ± 0	0.83 ± 0	0.66 ± 0	0.83 ± 0
A. baumannii	0.46 ± 0.34	0.61 ± 0.34	0.74 ± 0.34	0.74 ± 0	1.37 ± 1.38	0.62 ± 0	0.73 ± 0	0.83 ± 0	0.74 ± 0	0.57 ± 0
E. faecium	0.62 ± 0	1.16 ± 0	0.58 ± 0	0.37 ± 0.68	0.79 ± 0	0.79 ± 0	1.24 ± 0	1.33 ± 0	2.77 ± 0	1.10 ± 0

Synergy = <0.5, indifference = 0.5–4.0 or antagonism = >4.0. Au = gold, Cu = copper, Pt = platinum, Pd = palladium and Ag = silver (n = 3).