Table 3.

Synergistic activities between Cg-Defs, Cg-Prps, and Cg-BPI against selected bacteria expressed as a fractional inhibitory concentration (FIC index*).

FIC index	Gram-positive bacteria	Gram-negative bacteria
	M. lysodeikticus CIP5345	E. coli SBS 363	V. splendidus CIP 107715
Cg-Defh1 + Cg-Defh2	0.50	0.75	0.75
Cg-Defh1 + Cg-Defm	0.75	0.75	0.75
Cg-Defh2 + Cg-Defm	0.37	0.50	0.50
Cg-lgPrp + Cg-stPrp	2	2	2
Cg-Defh1 + Cg-lgPrp	0.35	0.50	2
Cg-Defh2 + Cg-lgPrp	0.30	0.28	2
Cg-Defm + Cg-lgPrp	0.45	0.75	2
Cg-BPI + Cg-lgPrp	nd	0.50	2
Cg-BPI + Cg-stPrp	nd	0.75	2
Cg-BPI + Cg-Defh1	0.45	0.26	2
Cg-BPI + Cg-Defh2	0.23	0.27	2
Cg-BPI + Cg-Defm	0.23	0.31	2

Adapted from Schmitt et al. (2012a).

*FIC index = [A]/MICA + [B]/MICB, where MICA and MICB are the MICs of peptides A and B alone and [A] and [B] are the MICs of peptides A and B in combination. The MICs for the peptides alone are as given in Table 2. When MIC values are superior to the highest concentration we tested, we chose this value as the MIC in the calculation of the FIC index. FIC index were interpreted as follows: ≤0.5, strong synergy; 0.5−1 synergy; ≥1; additive effect; =2, no effect; ≥2, antagonism. nd, not determined.