Photo-Activated Carbon Dots for Combating Drug Resistant Bacteria

Abstract

Bacterial infections are the major cause of infectious diseases and mortality. Antibiotics have been used as an effective treatment method because of the cost and their powerful effects. However, the widespread and the abuse of antibiotics have led to the emergence of many drug resistant bacterial strains. The crisis of bacterial resistance has promoted the global search for novel and effective alternative therapies to complement or replace existing antibiotics/antimicrobial treatments. This research focused on the assessment of the newly explored carbon dots (CDots) as a class of visible light activated antimicrobial agents against multidrug-resistant (MDR) bacteria, using different strains of MDR Enterococci (BM 46, BM 29, and 9756) and non drug-resistant strain (9144) as models, the antimicrobial activity of different concentrations of CDots were evaluated using the log reduction in viable cell number compared to the untreated controls. Several factors including treatment time, buffer, and light intensity were also investigated to examine their effects on the antimicrobial effectiveness of CDots. The study also explored the mechanism of action of CDots’ antimicrobial activity. The results indicated the intracellular reactive oxygen species (ROS) levels in bacteria increased dramatically upon CDots treatment, with ~290% to ~400% increases in tested Enterococcus strains. The addition of radical scavengers, L-Histidine, significantly protected cells from the antimicrobial activity of CDots, while tert-Butanol did not perceivably protect cells from inactivation by CDots, indicating that singlet oxygen is the primary ROS species generated by CDots treatment. The generation of ROS also caused lipid peroxidation in bacteria cells. Live and Dead staining assay and TEM imaging indicated increased cell membrane permeability and cytoplasmic disruption upon CDots treatment. Acknowledgement: The research was supported by NSF grants DMR# 1701399 and the NIH grant R15GM114752.