BACKGROUND: Heavy metal pollution may act as persistent selective pressure that favors the spread of antimicrobial resistance in natural environments. The aim of this study was to isolate and identify metal-tolerant bacteria from soils in olive tree fields routinely treated with copper-derived compounds and to evaluate the tolerance of bacterial strains to other metals and their resistance to clinically relevant antibiotics. RESULTS: Five hundred and ninety-five bacterial isolates from 45 olive tree agricultural fields were studied. Minimum inhibitory concentrations (MICs) ≥ 16 mmol L-1 were detected for copper (57% of isolates), zinc (37%) and lead (62%), while only 3% had MICs ≥ 12 mmol L-1 for nickel. Ninety-six metal-tolerant strains were selected for identification and antibiotic resistance determination. Most isolates belonged to the genera Pseudomonas (37%), Bacillus (23%) and Chryseobacterium (20%), while 6% were identified as Variovorax, 4% as Stenotrophomonas and 2% as Serratia or Burkholderia. Highest copper tolerance was detected among Pseudomonas. Over 75% of the strains with high copper tolerance were also resistant to vancomycin, 50% to ampicillin and 40% to erythromycin or trimethoprim/sulfamethoxazole. CONCLUSION: Bacteria from olive soils are tolerant to metals, mainly copper, but also zinc and lead, as well as resistant to clinically important antibiotics, which could be a troublesome issue in clinical settings.
BACKGROUND: Heavy metal pollution may act as persistent selective pressure that favors the spread of antimicrobial resistance in natural environments. The aim of this study was to isolate and identify metal-tolerant bacteria from soils in olive tree fields routinely treated with copper-derived compounds and to evaluate the tolerance of bacterial strains to other metals and their resistance to clinically relevant antibiotics. RESULTS: Five hundred and ninety-five bacterial isolates from 45 olive tree agricultural fields were studied. Minimum inhibitory concentrations (MICs) ≥ 16 mmol L-1 were detected for copper (57% of isolates), zinc (37%) and lead (62%), while only 3% had MICs ≥ 12 mmol L-1 for nickel. Ninety-six metal-tolerant strains were selected for identification and antibiotic resistance determination. Most isolates belonged to the genera Pseudomonas (37%), Bacillus (23%) and Chryseobacterium (20%), while 6% were identified as Variovorax, 4% as Stenotrophomonas and 2% as Serratia or Burkholderia. Highest copper tolerance was detected among Pseudomonas. Over 75% of the strains with high copper tolerance were also resistant to vancomycin, 50% to ampicillin and 40% to erythromycin or trimethoprim/sulfamethoxazole. CONCLUSION: Bacteria from olive soils are tolerant to metals, mainly copper, but also zinc and lead, as well as resistant to clinically important antibiotics, which could be a troublesome issue in clinical settings.
Authors: Sada M Boyd; Kristen L Rhinehardt; Akamu J Ewunkem; Scott H Harrison; Misty D Thomas; Joseph L Graves Journal: Antibiotics (Basel) Date: 2022-05-25