TABLE 2.

Activities of 10 antibiotics against isolates in wastewater effluent and downstream and upstream river watera

AntibioticActivityc against isolates fromb:
WWRWDRWU
Resistance prevalence (%)MIC (mg liter−1)Resistance prevalence (%)MIC (mg liter−1)Resistance prevalence (%)MIC (mg liter−1)
Range50%90%Range50%90%Range50%90%
Oxytetracycline94.71 to >1,024512>1,02486.20.5 to >1,0241281,0243.10.25 to 1280.52
Tetracycline95.21 to >1,024512>1,02485.11 to >1,0242561,0243.10.25 to 1280.52
Doxycycline83.10.5 to 1,02412825670.10.5 to 1,024645121.50.25 to 640.51
Ampicillin85.20.5 to >1,0242561,02493.11 to >1,02425651224.60.25 to 1,0248128
Cefotaxime71.40.25 to 1,0246425659.80.5 to 1,0241285121.50.25 to 2560.251
Kanamycin55.00.25 to >1,02412851270.10.5 to >1,0242561,0244.60.25 to 12818
Chloramphenicol72.50.5 to 1,02412851282.80.5 to 1,0241285129.20.25 to 512216
Ciprofloxacin9.00.25 to 1280.546.90.25 to 320.2547.70.25 to 320.250.25
Erythromycin92.10.25 to >1,0241281,02494.30.5 to 1,02412851224.60.25 to 512464
Rifampin88.40.5 to >1,0241281,02492.00.25 to 1,02412851226.20.25 to 5122128
  • a The 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.

  • b WW, wastewater effluent; RWD, downstream river water; RWU, upstream river water.

  • c Resistance 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.