Mercury Resistance in Bacterial Strains Isolated from Tailing Ponds in a Gold Mining Area Near El Callao (Bolívar State, Venezuela)
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Bacterial resistance to mercury (Hg) was investigated in strains isolated from Hg-contaminated tailing ponds located in the gold mining area of El Callao (Bolívar State, Venezuela). High frequencies of resistance were detected to both inorganic-Hg and organomercurials among these strains. A broad range of resistance levels was observed when determining minimal inhibitory concentrations of Hg2+. Some strains were able to grow in liquid medium containing 25 μM Hg2+, whereas others grew at 300 μM Hg2+. Of 190 Hg-resistant strains tested, 58.2% were additionally shown to be resistant to ampicillin (40 mg/L), 33.3% to chloramphenicol (30 mg/L), 24.9% to streptomycin (30 mg/L), 23.3% to tetracycline (30 mg/L), and 1.6% to kanamycin (30 mg/L). Furthermore, we found that 20% of the Hg-resistant strains were simultaneously resistant to as many as four of these antibiotics, at the concentrations tested. The presence of large plasmids in 62.9% of 53 Hg-resistant strains screened prompted us to investigate the horizontal transfer of resistance determinants. Mating experiments were performed using Escherichia coli and Pseudomonas aeruginosa as recipient strains. The results obtained confirmed that indigenous Hg-resistant bacteria colonizing the tailing ponds can effectively transfer the phenotype to potentially pathogenic species.
KeywordsHgCl2 Venezuela Resistance Determinant Mating Experiment Recipient Strain
We thank Ing. Elis Yegres and Lic. David Rondón (CVG-Minerven), as well as Ing. Máximo Benavides and María T. García (UNEXPO, Pto. Ordaz), for helping us during the collection of the samples. We are grateful to Luis Gutierrez (Lab. Espectroscopía Molecular, ULA) for the determination of soluble Hg by AAS and to Dr. Leonardo Serrano (Stanford University) for critical reading of the manuscript. This work was supported by Consejo de Desarrollo Científico, Humanístico y Tecnológico, CDCHT-ULA.
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