Co-effect of cadmium and iron oxide nanoparticles on plasmid-mediated conjugative transfer of antibiotic resistance genes Original paper

What was studied?

The study investigates the co-effects of cadmium (Cd²⁺) and iron oxide nanoparticles (Fe₂O₃) on plasmid-mediated conjugative transfer of antibiotic resistance genes (ARGs). Specifically, it explores how the combination of these environmental pollutants influences the horizontal gene transfer (HGT) process in microbial communities. The research uses the RP4 plasmid, known for facilitating the transfer of ARGs, to track how Cd²⁺ and Fe₂O₃ nanoparticles impact bacterial gene exchange and the subsequent spread of resistance traits, which can contribute to antimicrobial resistance.

Who was studied?

The study focused on bacterial strains from a water microbial community, using Pseudomonas putida KT2442 as the donor strain, which carries the RP4 plasmid. The recipient microbes were obtained from brackish water environments, providing a natural setting for studying gene transfer. The investigation centers on gram-negative bacteria, including human pathogens like Escherichia hermannii, Shigella boydii, and Klebsiella pneumoniae. These bacteria were subjected to various concentrations of Cd²⁺ and Fe₂O₃ nanoparticles to observe the effects on plasmid conjugation, with a particular focus on human pathogens that pose significant risks to public health.

Most important findings

The study found that the simultaneous exposure to Cd²⁺ and high concentrations of Fe₂O₃ nanoparticles significantly increased the conjugative transfer frequency of the RP4 plasmid compared to individual exposures. The highest transfer frequencies were observed when both pollutants were present, particularly with nano Fe₂O₃ at concentrations of 10 mg/L and 100 mg/L. Interestingly, the majority of the transconjugants identified were human pathogens, which emphasizes the potential public health implications of the findings. Mechanistically, the increased plasmid transfer was linked to enhanced cell membrane permeability, elevated antioxidant enzyme activities, and upregulated gene expression of conjugation-related genes (trbBp and trfAp). This suggests that the co-exposure to Cd²⁺ and nano Fe₂O₃ altered bacterial cell function, making it easier for plasmids to transfer between bacteria.

Key implications

This study highlights the potential risks posed by the combination of heavy metals and nanomaterials in the environment. The co-effect of Cd²⁺ and Fe₂O₃ nanoparticles can accelerate the spread of antibiotic resistance through enhanced horizontal gene transfer, especially in environments where human pathogens are prevalent. The findings stress the need for careful management of both heavy metal pollution and nanoparticle use, as they can inadvertently promote the dissemination of resistance genes, exacerbating the global challenge of antimicrobial resistance. Further studies are needed to understand the long-term ecological and public health impacts of these interactions and to develop strategies to mitigate the risks.