Anti-Rickettsial Activity of Chitosan, Selenium, and Silver Nanoparticles: Efficacy in Vero Cells

Nanoparticles have emerged as innovative tools for combating bacterial infections, offering a potential solution to antibiotic resistance and the limitations of conventional antimicrobials. Nanoparticles exhibit antibacterial activity through multiple mechanisms, including oxidative stress induction, metal ion release, direct membrane damage, disruption of DNA and proteins, and indirect immune system enhancement. <i>Rickettsia helvetica</i>, <i>R. monacensis</i>, <i>R. slovaca</i>, and <i>R. conorii</i> subsp. <i>raoultii</i> are tick-borne pathogens transmitted by <i>Ixodes ricinus</i>, <i>Dermacentor reticulatus</i>, and <i>D. marginatus</i> ticks across Europe causing spotted fever rickettsiosis. While rickettsioses are successfully treated with antibiotics, resistance of rickettsiae to antimicrobial therapy has been reported. Here, we evaluated the anti-rickettsial activity of silver (AgNPs), selenium (SeNPs), and chitosan (CSNPs) nanoparticles against <i>R. conorii</i> subsp. <i>caspia</i>, a tick-borne bacterial pathogen, in African green monkey kidney cell line (Vero). At their highest non-cytotoxic concentrations, CSNPs exhibited the strongest inhibitory effect (87%). SeNPs also significantly reduced bacterial load (76%), although their efficacy was constrained by cytotoxicity at higher doses. In contrast, AgNPs did not show significant activity under the tested conditions. The differences observed among nanoparticles reflect both the antimicrobial properties and host cell tolerance limits. These findings highlight CSNPs and SeNPs as promising candidates for further development of nanoparticle-based strategies to combat intracellular, tick-borne pathogens.