Table 5.

MIC data (μg/mL) for clindamycin and virginiamycin among E. faecalis and non–E. faecalis isolated from groundwater, surface water, or manure pits

	Clindamycina			Virginiamycina
Enterococcus spp. source	MIC50	MIC90	MIC range	MIC50	MIC90	MIC range
Up-gradient groundwater
E. faecalis (n = 12)	8	16	0.06–16	1	1	0.5–1
Non–E. faecalis (n = 18)	< 0.03	0.06	< 0.03–0.06	0.13	0.13	0.06–0.13
Down-gradient groundwater
E. faecalis (n = 21)	8	28.8	0.5–> 128	1	2	1–4
Non–E. faecalis (n = 5)	8	> 128	4–> 128	0.5	1	0.5–1
Up-gradient surface water
E. faecalis (n = 14)	16	32	8–32	1.5	8	0.5–8
Non–E. faecalis (n = 8)	16	64	4–64	1	2	0.5–2
Down-gradient surface water
E. faecalis (n = 80)	16	32	0.06–> 128	1	8	0.13–32
Non–E. faecalis (n = 27)	> 128	> 128	< 0.03–> 128	1	5.6	0.25–8
Manure pit
E. faecalis (n = 7)	128	> 256	64–> 256	8	16	2–16
Non–E. faecalis (n = 8)	192	> 256	8–> 256	1	32	0.5–32

MIC₅₀, MIC required to inhibit the growth of 50% of organisms.

^aCLSI resistance breakpoint for clindamycin and virginiamycin is ≥ 4 μg/mL (CLSI 2002).