This study investigated whether mercury exposure drives the carriage of antibiotic resistance genes in commensal Escherichia coli. Researchers analyzed 849 E. coli strains from four population groups with varying levels of mercury and antibiotic exposure: French pig farmers and bank workers (low mercury exposure), and Wayampi Amerindians and French expatriates in French Guyana (high and low mercury exposure, respectively). Mercury resistance was assessed by measuring minimum inhibitory concentrations (MICs) and detecting the merA gene. Mercury-resistant E. coli was significantly more prevalent in populations with higher antibiotic resistance rates. Specifically, French pig farmers showed higher mercury resistance carriage than matched controls, and Wayampi individuals exposed to mercury through gold mining activities exhibited both high mercury and antibiotic resistance despite minimal antibiotic use. The merA gene was detected in all mercury-resistant strains. The findings suggest that mercury exposure may select for bacteria carrying mercury resistance genes on transposons like Tn21, which also carry antibiotic resistance genes in class 1 integrons. This mechanism could explain high antibiotic resistance in populations with limited antibiotic exposure but significant environmental mercury contamination.

Key findings

• Mercury-resistant E. coli carriage was significantly higher in populations with elevated antibiotic resistance, in both French and French Guyana cohorts
• The merA gene was universally present in mercury-resistant strains and absent in sensitive strains, confirming genetic basis of resistance
• Wayampi Amerindians with documented high mercury exposure carried high rates of antibiotic-resistant E. coli despite minimal antibiotic use, suggesting mercury-driven selection
• Mercury resistance genes on Tn21-like transposons are genetically linked to antibiotic resistance genes in class 1 integrons, enabling co-selection
• Environmental mercury exposure may independently drive maintenance of antibiotic resistance genes without direct antibiotic selective pressure