Diffusion and enrichment of high-risk antibiotic resistance genes (ARGs) Original paper

What was studied?

This study explored the diffusion and enrichment of high-risk antibiotic resistance genes (ARGs) and pathogens through a transmission chain involving mulberry leaves, silkworm guts, silkworm feces, and soil in an ecological restoration area (RA) of a manganese mining site. The study aimed to assess how environmental factors, particularly heavy metals like manganese, zinc, and arsenic, influence the spread of antibiotic resistance through this transmission chain. The focus was on understanding how ARGs and pathogens are transferred and enriched in this ecological context, with the use of a plasmid (RP4) as a marker for horizontal gene transfer (HGT).

Who was studied?

The study focused on silkworm larvae (Bombyx mori) and their interaction with mulberry leaves grown in an ecological restoration area near a manganese mining site in Xiangtan, China. The researchers collected samples from both a restoration area (RA), contaminated with heavy metals, and a control area (CA), located farther from the mining site. The study analyzed the transmission of ARGs and pathogens through the ingestion of mulberry leaves by silkworms and subsequent microbial changes in their guts and feces. These samples were then added to soil to assess how ARGs and pathogens spread further into the environment.

What were the most important findings?

The study found that silkworms, after ingesting mulberry leaves from the restoration area (RA), enriched certain high-risk ARGs and pathogens in their feces, which were then transferred to the soil. The abundance of ARGs such as qnrB, oqxA, and rpoB increased significantly in feces from silkworms that ingested leaves from RA. The study also found that heavy metals like zinc, manganese, and arsenic played a crucial role in promoting the diffusion and enrichment of these ARGs in both silkworm feces and the soil. Interestingly, the presence of plasmid RP4, which mediates HGT, did not significantly contribute to the spread of ARGs due to the harsh survival conditions in the silkworm gut. However, the metal content in the environment enhanced the presence of certain high-risk ARGs, such as qnrB, oqxA, and rpoB, which were carried by pathogens like Klebsiella pneumoniae and Escherichia coli. After the silkworm feces were added to soil, the abundance of these ARGs increased by over four times within 30 days, indicating that the manure used as fertilizer in agricultural systems could be a significant vector for the spread of resistance genes.

What are the greatest implications of this study?

The findings highlight the risk of environmental contamination with antibiotic-resistant pathogens through agricultural practices, particularly in areas affected by mining activities. The study suggests that heavy metal contamination not only impacts microbial health but also promotes the spread of high-risk ARGs in the ecosystem. This has significant implications for public health, particularly in regions with a strong sericulture industry, where silkworm feces are commonly used as fertilizer. The study emphasizes the need for better management practices to prevent the spread of antibiotic-resistant pathogens through agricultural by-products and calls for more attention to the ecological risks associated with metal contamination in agricultural practices. Moreover, understanding the complex relationship between heavy metals, microbiota, and ARGs could inform strategies to mitigate the risks of environmental ARG transmission.