AI Insight
This study investigated the mercury resistance gene merA in human feces, chicken meat, and water samples from Japan, Vietnam, and Ghana using a newly developed PCR assay. Detection rates were significantly higher in Vietnam and Ghana compared to Japan across all sample types, with human fecal carriage reaching 70-97% in Vietnam and Ghana versus only 7% in Japan. The merA gene was found on a mobile plasmid in isolated Citrobacter freundii bacteria, suggesting it can spread between bacterial species through horizontal gene transfer.
Why it matters
The findings suggest that fecal merA detection could serve as a sensitive biomarker for assessing population-level mercury exposure and associated health risks, potentially offering advantages over traditional chemical testing methods. The high prevalence in developing countries indicates greater environmental mercury contamination and raises concerns about antibiotic resistance co-selection in these regions.
Understand the Science
by Yen Hai Le, Judith Dzifa Azumah, Diep Thi Khong, Thang Nam Nguyen, Cornelia Appiah-Kwarteng, Kazuaki Matsui, Mayumi Yamamoto, Kaori Tanaka, Yoshimasa Yamamoto
In this study, we investigated the prevalence and abundance of the mercury resistance gene merA in human feces, retail chicken meat, and environmental water samples collected from Japan, Vietnam, and Ghana. A real-time PCR assay developed in this study demonstrated high specificity toward merA sequences from more than 12 bacterial species. Using this assay, merA was detected in 6.8% of human fecal samples in Japan (n = 29), in contrast to significantly higher rates observed in Vietnam (70.2%, n = 47) and Ghana (97.4%, n = 39). Similar geographic trends were evident in the chicken meat samples: 18.5% in Japan (n = 27), 66% in Vietnam (n = 91), and 90% in Ghana (n = 10). Environmental water samples showed a consistently high merA detection rate across all countries (75–100%, n = 21), with substantially higher gene copy numbers in Vietnam and Ghana than in Japan. merA was detected in some water samples, even when total mercury concentrations were below the detection limit, indicating that molecular detection may offer greater sensitivity than traditional physicochemical methods. Mercury-resistant bacteria were successfully isolated and cultured, and Citrobacter freundii was identified as the representative strain. Genomic analysis revealed that merA was located on an IncFIB plasmid, flanked by insertion sequences, suggesting its potential for horizontal gene transfer. These findings highlight merA as a promising biomarker for environmental mercury exposure and support the utility of fecal merA analysis as a proxy for assessing mercury-related public health risks.