Is exposure to mercury a driving force for the carriage of antibiotic resistance genes?

The mercury resistance gene merA has often been found together with antibiotic resistance genes in human commensal Escherichia coli. To study this further, we analysed mercury resistance in collections of strains from various populations with different levels of mercury exposure and various levels of antibiotic resistance. The first population lived in France and had no known mercury exposure. The second lived in French Guyana and included a group of Wayampi Amerindians with a known high exposure to mercury. Carriage rates of mercury resistance were assessed by measuring the MIC and by detecting the merA gene. Mercury-resistant E. coli was found significantly more frequently in the populations that had the highest carriage rates of antibiotic-resistant E. coli and in parallel antibiotic resistance was higher in the population living in an environment with a high exposure to mercury, suggesting a possible co-selection. Exposure to mercury might be a specific driving force for the acquisition and maintenance of mobile antibiotic resistance gene carriage in the absence of antibiotic selective pressure.