Due to the physicochemical properties of nanoparticles, the use of nanomaterials increases every year in industrial and medical processes. At the same time, the increasing number of bacteria becoming resistant to many antibiotics, mostly by a horizontal gene transfer process, is a major public health concern. Could there be a link between nanoparticles and physiological induction of horizontal gene transfer in bacteria?
The
Proteomics, Metals and Differentiationteam of the Chemistry and Biology of Metals Laboratory is studying the response of living organisms to exposure to metallic nanoparticles. In this context, this team studied the response of a soil bacterium,
Bacillus subtilis, to nanoparticles of zinc oxide, silver and titanium oxide. The team focused in particular on the phenomenon of bacterial competence, which corresponds to the ability of bacteria to internalize foreign DNA without a species barrier. If this foreign DNA contains genes and integrates with the bacterial chromosome or a plasmid (replicative extra-chromosomal DNA often carrying resistance to antibiotics), these genes will be conserved and can be expressed in the recipient bacterium. This mechanism, called horizontal transfer, is one of the major mechanisms of diffusion of resistances.
In this context, researchers have shown that bacterial competence can be modified by the presence of nanoparticles in the medium (Figure), even without direct contact between nanoparticles and bacteria. Bacteria are then cultured on a Petri dish, therefore without direct contact with the nanoparticles, which are dispersed in the solid medium. These results are different from the observations presented in the literature which described an increased DNA transfer in the presence of nanoparticles. These latter observations were based on the "sandpaper" effect, linked to the abrasion of the bacterial wall by the nanoparticles under the culture conditions used in these cases (liquid medium with stirring). Different effects were observed for the nanoparticles tested: zinc oxide increases bacterial competence, titanium oxide decreases it, and silver has no effect
(Figure).
This article raises several important issues for the future in ecotoxicological and toxicological terms. For example, what could be the influence of certain ingested nanoparticles on the bacteria of the digestive tract, and in particular the transfer of antimicrobial resistance? Other studies, involving different bacteria and nanoparticles, are needed and will be conducted by the researchers on this team.
This work was funded by the SERENADE labex.