Different Fitness Costs during Biofilm Growth from Antibiotic-Resistant Bacteria to Antibiotic-Sensitive Bacteria under the Toxicity Stress of Copper Substrate

In water supply systems, copper pipes are commonly used to prevent bacterial growth and biofilm formation. However, it is uncertain whether copper can effectively inhibit antibiotic-resistant bacterial (ARB) biofilm formation, which is crucial for water supply safety. This study examined the difference in biofilm formation between ARB and antibiotic-sensitive bacteria (ASB) on copper surfaces by measuring the extracellular polymeric substance (EPS) content. In the blank control group, ASB biofilms outperformed ARB biofilms; however, when exposed to copper, the bacterial abundance of ARB biofilms was 10^0.5–10^1.0 times higher than that of ASB biofilms, and the EPS content was also 10^1.1–10^1.9 times higher. This disparity was mainly attributed to the varying fitness costs of the ARB in different environments. Furthermore, the oxidative stress response of ARB was significantly lower than that of ASB on a copper substrate, and the intracellular reactive oxygen species (ROS) level in ARB was only 78.7% of that of ASB. Gene expression patterns revealed that ARB biofilm formation on the copper substrate was mainly caused by the c-di-GMP-activated signaling pathway rather than the SOS stress system activated by ROS. These findings have implications for the choice of copper products in water supply systems.