Antibiotic-resistant Escherichia coli transconjugants obtained from bacteria of mine soil amended with organic wastes. MineTransconjugants

Heavy metal resistance has been associated to antibiotic resistance, due to co-resistance or cross-resistance mechanisms. Therefore, metal contaminated mine soil can be considered as an environment that facilitates the dissemination of antibiotic resistance genes. Similarly, due to the administration of antibiotics to livestock, soils amended with animal manure often present mobile genetic elements harbouring antibiotic resistance genes. This work was focused on (i) the search of mobile genetic elements (i.e. plasmids, integrons) in metal contaminated mine soils amended with organic wastes, and (ii) the study of the ecological fitness of antibiotic-resistant Escherichia coli transconjugants obtained from bacteria present in those soils. In our amended mine soils, from TC-DNA samples, we detected conjugative⁄mobilizable IncP-1 and IncQ plasmids and class 1 integron integrase intl1 sequences, indicating that bacteria from these soils have gene-mobilizing capacity with implications for the dissemination of resistance factors. We obtained a total of 17 E. coli putative transconjugants selected with ampicillin, erythromycin, chloramphenicol or streptomycin by exogenous plasmid isolation. ?Almost all putative transconjugants ?displayed a multi-resistant phenotype against a broad spectrum of antibiotics, including one harbouring imipenem resistance. Antibiotic resistance, possibly by acquisition of plasmids in putative transconjugants also appeared to affect ecological fitness traits such as RNA:DNA ratio, growth rate, gyrase activity, carbon substrate utilization patterns and biofilm formation. We concluded that the metal-contaminated, organically-amended mine soil studied is an important reservoir of conjugative/mobilizable plasmids with multiple antibiotic resistance genes.