Table 2.

Lowest σfic indices for binary combinations of selected α-hydrazido acids and first-line antibiotics toward drug-sensitive and drug-resistant strains ^a.

ΣFIC vs. Drug Sensitive Bacteria ([H]/[X]) b for Combinations with the Indicated Antibiotics
Compd	S. aureus ATCC 29213 c		S. aureus SA1199 d	E. coli ATCC 25922 c
	Tetracycline		Ciprofloxacin	Tetracycline
A	0.50 (1/0.0313)		2 (8/0.16)	0.38 (1/0.0625)
B	0.38 (1/0.0156)		0.75 (4/0.08)	0.50 (2/0.125)
ΣFIC vs. Drug Resistant Bacteria ([H]/[X]) b for Combinations with the Indicated Antibiotics
	S. aureus AOUC-0915 (LR-MRSa) e		S. aureus SA1199B f	E. coli 288328 (GR-CREc) g
	Methicillin h	Linezolid	Ciprofloxacin	Colistin	Gentamicin
A	0.5 < ΣFIC ≤ 0.53 (2/64)	1.03 (0.125/16)	0.75 (4/2.5)	0.31 (1/0.5)	1.25 (1/128)
B	0.5 < ΣFIC ≤ 1.0 (2/1024)	1.03 (0.125/16)	0.5 (4/2.5)	0.28 (2/0.25)	1.50 (4/128)

^a Cells with cases of synergy are reported in light green. ^b [H] indicates the concentration of α-hydrazido acid in μg/mL, whereas [X] are the concentrations of the indicated antibiotics in μg/mL. ^c MICs of tetracycline alone: 0.125 μg/mL for S. aureus ATCC 29213, 0.5 μg/mL for E. coli ATCC 25922. ^d Ciprofloxacin-susceptible S. aureus SA1199. MIC of ciprofloxacin alone: 0.16 μg/mL. ^e Linezolid- and methicillin-resistant S. aureus AOUC-0915. MICs of antibiotics alone: 16 μg/mL for linezolid, >1024 μg/mL for methicillin. ^f Ciprofloxacin-resistant S. aureus SA1199B. MIC of ciprofloxacin alone: 10 μg/mL. ^g Gentamicin- and colistin-resistant E. coli 288328. MICs: 128 μg/mL for gentamicin, 8 μg/mL for colistin. ^h The exact MIC for methicillin could not be obtained; thus, the upper and lower limits in reported ranges were calculated using the minimum possible value (2048 μg/mL) and an infinite value, respectively, for the actual methicillin MIC.