TABLE 2.

Activities of 10 antibiotics against isolates in wastewater effluent and downstream and upstream river water^a

Antibiotic	Activityc against isolates fromb:
	WW				RWD				RWU
	Resistance prevalence (%)	MIC (mg liter−1)			Resistance prevalence (%)	MIC (mg liter−1)			Resistance prevalence (%)	MIC (mg liter−1)
		Range	50%	90%		Range	50%	90%		Range	50%	90%
Oxytetracycline	94.7	1 to >1,024	512	>1,024	86.2	0.5 to >1,024	128	1,024	3.1	0.25 to 128	0.5	2
Tetracycline	95.2	1 to >1,024	512	>1,024	85.1	1 to >1,024	256	1,024	3.1	0.25 to 128	0.5	2
Doxycycline	83.1	0.5 to 1,024	128	256	70.1	0.5 to 1,024	64	512	1.5	0.25 to 64	0.5	1
Ampicillin	85.2	0.5 to >1,024	256	1,024	93.1	1 to >1,024	256	512	24.6	0.25 to 1,024	8	128
Cefotaxime	71.4	0.25 to 1,024	64	256	59.8	0.5 to 1,024	128	512	1.5	0.25 to 256	0.25	1
Kanamycin	55.0	0.25 to >1,024	128	512	70.1	0.5 to >1,024	256	1,024	4.6	0.25 to 128	1	8
Chloramphenicol	72.5	0.5 to 1,024	128	512	82.8	0.5 to 1,024	128	512	9.2	0.25 to 512	2	16
Ciprofloxacin	9.0	0.25 to 128	0.5	4	6.9	0.25 to 32	0.25	4	7.7	0.25 to 32	0.25	0.25
Erythromycin	92.1	0.25 to >1,024	128	1,024	94.3	0.5 to 1,024	128	512	24.6	0.25 to 512	4	64
Rifampin	88.4	0.5 to >1,024	128	1,024	92.0	0.25 to 1,024	128	512	26.2	0.25 to 512	2	128

^aThe Exiguobacterium spp. and Microbacterium spp. strains for which there were still no interpretive criteria according to CLSI standards were not taken into account when determining antibiotic activities.

^bWW, wastewater effluent; RWD, downstream river water; RWU, upstream river water.

^cResistance prevalence for the indicated antibiotic in the bacterial population was calculated as the ratio of the number of resistant strains versus the total number of strains in the population. 50%, MIC₅₀; 90%, MIC₉₀. The range of MICs of each antibiotic for all tested isolates in WW, RWD, and RWU, respectively, is shown.