. 2007 Mar 22;115(7):1040–1045. doi: 10.1289/ehp.9770

Table 4.

MIC data (μg/mL) for erythromycin, tetracycline, and vancomycin among Enterococcus spp. isolated from groundwater, surface water, or manure pits.

	Erythromycin^a			Tetracycline^a			Vancomycin^a
Enterococcus spp. source	MIC₅₀	MIC₉₀	MIC range	MIC₅₀	MIC₉₀	MIC range	MIC₅₀	MIC₉₀	MIC range
Up-gradient groundwater (n = 30)	16	60.8	1–128	< 1	< 1	< 1–32	0.25	58	0.25–> 64
Down-gradient groundwater (n = 26)	2	> 256	< 0.5–> 256	2	64	< 1–> 256	4	8	0.25–8
Up-gradient surface water (n = 22)	1	2	< 0.5–4	< 1	108.8	< 1–128	2	8	0.5–8
Down-gradient surface water (n = 107)	2	> 256	< 0.5–> 256	2	153.6	< 1–> 256	2	8	0.25–> 64
Manure pit (n = 15)	> 256	> 256	< 0.5–> 256	128	179.2	< 1–> 256	0.5	2	0.5–2

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

CLSI resistance breakpoints are as follows: erythromycin, ≥ 8 μg/mL; tetracycline, ≥ 16 μg/mL; vancomycin, ≥ 32 μg/mL (CLSI 2002).