Carbon nanodots as photosensitizer in photodynamic inactivation of Rickettsia slovaca.

Carbon quantum dots (CQDs) are promising therapeutic agent due to their pro-oxidant, antioxidant, antiviral, antibacterial, and anticancer properties when exposed to visible light irradiation. Oxidative stress in bacteria is the main reason for bacteria death after exposure to blue light photoexcited quantum dots. Herein, we present the antibacterial activities of hydrophobic carbon quantum dots/polydimethylsiloxane nanocomposites, hydrophilic citric acid CQDs, and combinations of CQDs with methylene blue. We investigated the antirickettsial effect of hydrophilic and hydrophobic CQDs against Rickettsia slovaca, a tick-borne bacterial pathogen. Photodynamic activity against on rickettsiae reached 99.66% using CQDs with 470 nm blue light irradiation. Combining methylene blue with CQDs further enhanced the effect on rickettsial infection, achieving 99,98% efficacy. The obtained results reveal the in vitro antirickettsial properties of CQDs. Sequencing analysis on the genomic level of control and treated samples showed single nucleotide variants (SNVs). Based on snippy analysis SNVs were assigned to the rRNA genes, 16S rRNA and 30S rRNA genes. By freebayes analysis in treated samples, a stop-lost mutation was detected in pseudogene (RSL_RS06070), while the possible effect on down-stream genes including tsaD, acyl-CoA-desaturase, 30S ribosomal protein S6 and DUF424 family protein. The frameshift mutation was localized within clpB pseudogene belonging to stress-response heat-shock proteins.