Published in PLOS One on 2026-09-08, this study is presented as an attributed evidence briefing. The excerpts below are the original researchers’ words, reproduced under their Creative Commons Attribution licence. Health Signal has selected the abstract and, where needed, opening background paragraphs; the complete methods, results, limitations and references remain in the linked paper.
Original authors: Yen Hai Le, Judith Dzifa Azumah, Diep Thi Khong, Thang Nam Nguyen, Cornelia Appiah-Kwarteng, Kazuaki Matsui, Mayumi Yamamoto, Kaori Tanaka, Yoshimasa Yamamoto, Naser Anjum, Rajesh Singh Rathore, Xin Sun, Ali Hasan
Source: PLOS One • DOI 10.1371/journal.pone.0357976
Read the complete primary study ↗ · Creative Commons Attribution licence
From the researchers
Abstract
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.
Introduction
Mercury (Hg) is a widespread environmental pollutant due to its ubiquitous presence in nature and continuous release into soil and water. Both anthropogenic activities, such as mining, and natural processes, including volcanic eruptions and wildfires, contribute to Hg contamination of the environment [1]. Small-scale gold mining is a major contributor to global Hg emissions, especially in African countries such as Ghana [2].
In contaminated environments, the predominant inorganic form of Hg is Hg(II), which is highly toxic because of its strong affinity for cellular thiol groups, leading to disruption of essential biological functions. The bacterial merA gene plays a key role in detoxifying Hg(II) by reducing it to the less toxic and volatile elemental Hg (Hg0). In contrast, methylmercury (MeHg) is the Hg species of greatest concern for human health because it readily bioaccumulates and biomagnifies through aquatic and terrestrial food webs. Consequently, humans, as top-level consumers, are particularly vulnerable to MeHg exposure through dietary intake [3–5]. Accordingly, systematic surveillance of Hg contamination across environmental and dietary sources is a critical component of public health protection. Importantly, the World Health Organization (WHO) sets a guideline value of 0.006 mg/L for total Hg in drinking water [6]. However, national standards in both Vietnam [7] and Ghana [8] impose a more stringent maximum permissible concentration of 0.001 mg/L for both drinking and surface water, above which Hg exposure is considered hazardous to human health.
Reading this evidence
Use the full paper to check the study design, participant selection, comparator and outcome definitions before drawing a practical conclusion. An association does not by itself show cause and effect. A reported performance measure needs its denominator and uncertainty. A finding from a particular facility, sample or time period should retain that scope when it is discussed elsewhere.
This briefing makes the source accessible within the wider public health desk. It does not assess an individual patient or certify a product. When considering relevance to another health system, examine the original authors’ account of context and limitations, then seek local implementation evidence. The related reporting below provides other studies to read alongside this one; it is a topic connection, rather than a claim that their results are directly comparable.
© 2026 Yen Hai Le, Judith Dzifa Azumah, Diep Thi Khong, Thang Nam Nguyen, Cornelia Appiah-Kwarteng, Kazuaki Matsui, Mayumi Yamamoto, Kaori Tanaka, Yoshimasa Yamamoto, Naser Anjum, Rajesh Singh Rathore, Xin Sun, Ali Hasan. Excerpts reproduced under CC BY. Selection, formatting and contextual notes by Health Signal. The researchers are the authors of the source study, not members of Health Signal’s staff.
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