. 2019 Sep 18;10:2153. doi: 10.3389/fmicb.2019.02153

TABLE 1.

MICs for numerous antibiotics against S. aureus efflux pump over-expressed/deletion strains in the absence and presence of RP2.

Compounds	S. aureus SA1199B (NorA⁺⁺)			S. aureus K1758 (NorA^–)
	MIC^a	MIC^b	FICI^c	MIC^a	MIC^b	FICI^c
Norfloxacin	32	0.5 (32)	0.265	0.25	0.125 (16)	0.75
		2 (16)	0.1875		0.25 (8)	–
		4 (8)	0.1875		0.25 (4)	–
		8 (4)	0.281		0.25 (2)	–
Ciprofloxacin	8	0.5 (32)	0.3125	0.125	0.125 (16)	–
		1 (16)	0.25		0.125 (8)	–
		4 (8)	0.5625		0.125 (4)	–
Moxifloxacin	0.25	0.0625 (32)	0.375	0.0625	0.0625 (16)	–
		0.125 (16)	0.625		0.0625 (8)	–
Chloramphenicol	8	2 (32)	0.375	2	2 (16)	–
		4 (16)	0.625		2 (8)	–
RP2	128	n/a	n/a	64	n/a	n/a

	S. aureus XU212 (TetK)^∗			S. aureus RN4220-MsrA^∗∗

Tetracycline¹/Erythromycin²	128	2 (32)	0.265	128	4 (32)	0.281
		4 (16)	0.156		16 (16)	0.25
		8 (8)	0.125		32 (8)	0.3125
		32 (4)	0.281		64 (4)	0.531
RP2	128	n/a	n/a	128	n/a	n/a

MIC^a, minimum inhibitory concentration of compound alone (μg/mL); MIC^b, MIC of antibiotic in the presence of RP2 (μg/mL in parentheses); FICI^c, fractional inhibitory concentration index. The checkerboard synergy assay of RP2 in combination with Tetracycline¹ and Erythromycin² was performed against S. aureus XU212^∗ and S. aureus RN4220-MsrA^∗∗, respectively.⁺⁺, NorA over-expressed strain; ^––, NorA deletion strain.