Table 1 Interactions of 4-(5-methyl-1,3,4-thiadiazol-2-yl) benzene-1,3-diol (denoted by C1) with amphotericin B (AmB) in in vitro combating pathogenic fungal isolates and reference strains obtained after 48-h culture with the checkerboard microdilution method; 100% inhibition of growth was taken as the MIC value.

Strain	Separate treatment		Combinatory treatment
	Separate treatment		2 µg/mL C1		4 µg/mL C1		8 µg/mL C1		16 µg/mL C1		32 µg/mL C1		64 µg/mL C1
	MIC C1 [µg/mL]	MIC AmB [µg/mL]	MIC AmB [µg/mL]	∑FIC	MIC AmB [µg/mL]	∑FIC	MIC AmB [µg/mL]	∑FIC	MIC AmB [µg/mL]	∑FIC	MIC AmB [µg/mL]	∑FIC	MIC AmB [µg/mL]	∑FIC
Candida albicans isolate 102	32	0.5	0.25	0.56*	0.125	0.38**	0.0625	0.37**	0.0312	0.56*	—	—	—	—
Candida krusei isolate 93	64	0.5	0.25	0.53*	0.125	0.31**	0.0625	0.24**	0.0312	0.31**	0.0156	0.52*	—	—
Candida dubliniensis isolate 176	8	0.5	0.0625	0.37**	0.0078	0.52*	—	—	—	—	—	—	—	—
Candida glabrata isolate 124	96	1.0	1.0	1.02	1.0	1.04	1.0	1.17	0.25	0.42**	0.0078	0.34**	0.0078	0.67*
Candida krusei isolate 103	96	1.0	1.0	1.02	0.5	0.54*	0.25	0.33**	0.25	0.42**	0.0625	0.39**	0.0078	0.67*
Candida tropicalis isolate 175	96	1.0	1.0	1.02	1.0	1.04	0.5	0.58*	0.25	0.42**	0.0625	0.39**	0.0078	0.67*
Trichophyton rubrum ATCC 28188	32	0.25	0.125	0.31**	0.125	0.37**	0.125	0.5**	0.0625	0.62*	—	—	—	—
Rhodotorula mucilaginosa ATCC 22273	32	1.0	0.5	0.56*	0.25	0.37**	0.125	0.37**	0.0312	0.53*	—	—	—	—
Aspergillus niger ATCC 16888	64	1.0	0.125	0.16**	0.0625	0.12**	0.0312	0.16**	0.0312	0.28**	0.0312	0.53*	—	—
Candida albicans NCPF 3153	96	0.5	0.25	0.52*	0.125	0.29**	0.125	0.33**	0.0625	0.29**	0.0312	0.40**	0.0312	0.73*
Candida parapsilosis ATCC 22019	64	2.0	0.5	0.28**	0.25	0.19**	0.125	0.19**	0.0625	0.28**	0.0625	0.53*	—	—

The MIC value of AmB [µg/mL] in the presence of the C1 in a concentration range of 2–64 g/mL and ∑FIC (sum of fractional inhibitory concentrations) are presented. The interpretation of the interactions is shown as follows: **synergy (∑FIC ≤ 05), *additivity (∑FIC > 0.5 to ≤1), lack of a label means a non-differentiating effect (∑FIC > 1 to < 2), no antagonistic interactions (∑FIC ≥ 2) were observed in any combination of the concentrations. ∑FIC = FIC_AmB + FIC_C1, where: FIC_AmB = MIC_AmB in the presence of C1/MIC_{AmB alone}; FIC_C1 = MIC_C1 in the presence of AmB/MIC_{C1 alone}.

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