The effects of the combined use of carbon quantum dots and antibacterial agents on pathogenic bacteria.

Background/aim: This study evaluates the challenges associated with overcoming antimicrobial resistance and innovative approaches to combat multidrug-resistant (MDR) bacterial infections. Materials and methods: Novel codoped carbon quantum dots (CCQDs) were synthesized using citric acid as the carbon source and L-cysteine as the nitrogen codoping atom. The formulation in which citric acid was retained was designated as CCQDs-1, whereas the purified version, from which citric acid was removed, was termed CCQDs-2. The antibacterial properties of CCQDs-1 and CCQDs-2 were compared using the agar well diffusion method. This study comprehensively characterizes these nanomaterials and evaluates their antibacterial potential, both alone and in combination with antibiotics, against a spectrum of gram-positive (G+) and gram-negative (G-) bacterial strains. Results: The study demonstrates the significant antibacterial efficacy of CCQDs, with notable variations observed between citric acid-containing and citric acid-neutralized formulations. The QDs exhibited remarkable characteristics, including a quantum yield of 90.3%-90.6%, intense fluorescence, and distinctive interactions with various antibiotics. In addition to their intrinsic antibacterial activity, the QDs also exhibited synergistic effects when combined with certain antibiotics. A synergistic effect was particularly observed when CCQDs-2 were combined with antibiotics such as gentamicin, levofloxacin, and clindamycin, suggesting potential mechanisms such as membrane permeability disruption and efflux pump saturation. Conclusion: These findings underscore the promising potential of carbon-based QDs as innovative, biocompatible solutions to address the critical global challenge of antimicrobial resistance.