title: Copper amendment of agricultural soil selects for bacterial antibiotic resistance in the field.
abstract: OBJECTIVE
  The objective of this study was to determine whether Cu-amendment of field plots affects the frequency of Cu resistance, and antibiotic resistance patterns in indigenous soil bacteria.
  
  
  RESULTS
  Soil bacteria were isolated from untreated and Cu-amended field plots. Cu-amendment significantly increased the frequency of Cu-resistant isolates. A panel of isolates were characterized by Gram-reaction, amplified ribosomal DNA restriction analysis and resistance profiling against seven antibiotics. More than 95% of the Cu-resistant isolates were Gram-negative. Cu-resistant Gram-negative isolates had significantly higher incidence of resistance to ampicillin, sulphanilamide and multiple (> or =3) antibiotics than Cu-sensitive Gram-negative isolates. Furthermore, Cu-resistant Gram-negative isolates from Cu-contaminated plots had significantly higher incidence of resistance to chloramphenicol and multiple (> or =2) antibiotics than corresponding isolates from control plots.
  
  
  CONCLUSIONS
  The results of this field experiment show that introduction of Cu to agricultural soil selects for Cu resistance, but also indirectly selects for antibiotic resistance in the Cu-resistant bacteria. Hence, the widespread accumulation of Cu in agricultural soils worldwide could have a significant effect on the environmental selection of antibiotic resistance.
authors.affiliation: Department of Ecology, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark.
authors.forename: J
authors.initials: J
authors.lastname: Berg
authors.forename: A
authors.initials: A
authors.lastname: Tom-Petersen
authors.forename: O
authors.initials: O
authors.lastname: Nybroe
mesh_terms: D000383:Agriculture; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003300:Copper / Q000008:administration & dosage* / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D015183:Restriction Mapping; D012987:Soil / Q000032:analysis; D012988:Soil Microbiology
chemical_list: D000900:Anti-Bacterial Agents; D012987:Soil; D003300:Copper