Effects of nano-TiO₂ on antibiotic resistance transfer mediated by RP4 plasmid

Abstract

The potential risks of nano-materials and the spread of antibiotic resistance genes (ARGs) have become two major global public concerns. Studies have confirmed that nano-alumina can promote the spread of ARGs mediated by plasmids. Nano-titanium dioxide (TiO₂), an excellent photocatalytic nano-material, has been widely used and is often present in aqueous environments. At various nano-material concentrations, bacterial density, matting time, and matting temperature, nano-TiO₂ can significantly promote the conjugation of RP4 plasmid in Escherichia coli. We developed a mathematical model to quantitatively describe the conjugation process and used this model to evaluate the effects of nano-TiO₂ on the spread of ARGs. We obtained analytical solutions for total and resistant bacteria, which were enumerated by the abundance of genetic loci unique to the plasmid and the chromosome using qPCR. Our results showed that the mathematic model was able to fit the experimental data well and can be used to quantitatively evaluate the effects of nano-TiO₂. According to our model, the presence of nano-TiO₂ decreased the bacterial growth rate from 0.0360 to 0.0323 min⁻¹ and increased the conjugative transfer rate from 6.69 × 10⁻¹² to 3.93 × 10⁻¹⁰mL cell⁻¹ min⁻¹. These results indicate that nano-TiO₂ inhibited bacterial growth and promoted conjugation simultaneously. The data for morphology and mRNA expression also demonstrated this phenomenon. Our results confirm that environmental nano-TiO₂ may cause the spread of ARGs and thus poses an environmental risk. In addition, we provide a potential method for monitoring changes in ARGs that result from conjugation and evaluating the effects of antimicrobial substances on ARG expression.

• Conjugation
• conjugative transfer rate
• environmental risk
• growth rate
• public concerns
• spread of ARGs

Acknowledgements

We thank Prof. Julian E. Davies (University of British Columbia) for providing the RP4 plasmid and Dr. Zhijiang Wang (Tianjin University, China) for assistance with data analysis.

Declaration of interest

The authors declare no competing financial interests. This work was supported by the National Natural Science Foundation of China (Grant 81202163 and 81372947) and the Natural Science Foundation of Tianjin China (Grant 13JCYBJC19900).

Supplementary material available online

Supplementary Figures S1–S2 and Supplementary Text S1