Regulatory mechanism of montmorillonite on antibiotic resistance genes in Escherichia coli induced by cadmium.

The emergence and spread of antibiotic resistance genes (ARGs) induced by the overuse of antibiotics has become a serious threat to public health. Heavy metals will bring longer-term selection pressure to ARGs when the concentration of their residues is higher than that of antibiotics in environmental media. To explore the potential roles of montmorillonite (Mt) in the emergence of ARGs under divalent cadmium ion (Cd2+) stress, Escherichia coli (E. coli) was induced continuously for 15 days under Cd2+ gradient concentrations (16, 32, 64, 96, and 128 μg∙mL-1) with and without Mt. Subsequently, antibiotic resistance testing, transcriptomics, transmission electron microscope, scanning electron microscopy, and Fourier transform infrared were conducted for analysis. The results of characterization analysis showed that Cd2+could enhance the expression of resistance genes such as penicillin, tetracycline, macrolactone, and chloramphenicol in E. coli. Moreover, compared with Cd2+, Mt-Cd could inhibit the promotion of these resistances by alleviating the expressions of genes involved in cell wall/membrane, protein synthesis, transport systems, signal transduction, and energy supply processes. Therefore, the study promoted the understanding of Cd2+ in triggering bacterial antibiotic resistance and highlighted a novel theme of clay's ability to mitigate ecological risk of antibiotic resistance caused by heavy metals. KEY POINTS: • Montmorillonite (Mt) could inhibit the promotion of antibiotic resistances. • E. coli formed a unique resistance mechanism by interacting with Mt and Cd2+. • Mt stimulated cellular signal transduction, cellular component, and energy supply.