A correlation analysis between arsenic and mercury resistance and the spread of antibiotic resistance genes in bacteria isolated from a highly contaminated brownfield.

Seventy-four bacterial strains from El Terronal (Asturias, Spain), a brownfield highly contaminated with mercury and arsenic but without anthropogenic antibiotic influx, were isolated and characterized in culture. No correlation was found between resistance to the aforementioned metal(loid)s and to antibiotics and biocides as tested by agar plates and disk diffusion method, as the number of strains deemed resistant to any of the analyzed antibiotics and biocides was not significantly higher among those with the highest resistance to arsenic and/or mercury. Genome sequencing of 17 of the isolated strains revealed a great number and diversity of antibiotic resistance genes (ARGs), as well as genes related to arsenic and mercury resistance, some of which were located in mobile genetic elements (MGEs). However, most of the detected ARGs were not located in MGEs, and no genes responsible for metal(loid) and antibiotic resistance were found to share an MGE. No evidence was found that resistance to arsenic and mercury influenced the dissemination of ARGs in the studied strains, although the abundance of antibiotic resistance mechanisms related to the presence of RND-type (Resistance-Nodulation-Division) efflux pumps could potentially contribute to cross-resistance.