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Keywords:

  • amplified ribosomal DNA restriction analysis;
  • community structure;
  • copper resistance;
  • culturable bacteria

Abstract

Aims:  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.

Methods and 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 (≥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 (≥2) antibiotics than corresponding isolates from control plots.

Significance and Impact of the Study:  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.