In vitro evaluation of the antimicrobial effect of ZnO:9Ag nanoparticle and antibiotics on standard strains of Leptospira spp

Silver nanoparticles are recognized for potent antimicrobial properties against pathogenic bacteria, crucial in addressing the severity of leptospirosis, where an ideal treatment is lacking. This study focuses on assessing the antimicrobial efficacy of silver-doped zinc oxide nanoparticles (ZnO:9Ag) on standard Leptospira spp. strains (six species and ten serovars). Comparisons with conventional antibiotics were made. In vitro characterizations, including minimum inhibitory concentration (MIC), cell viability, membrane permeability, intracellular content release, and broth microdilution checkerboard assay, evaluated streptomycin, penicillin G, doxycycline, tetracycline, and ZnO:9Ag effects on Leptospira. The safety and toxicological effects of ZnO:9Ag were explored using the chicken embryo in vivo model. All treatments displayed notable anti-Leptospira effects. Penicillin G had a lower MIC (<0.048), contrasting ZnO:9Ag's higher MIC (6.25 to 50 μg/mL). Despite this, ZnO:9Ag exhibited pronounced inhibitory effects, making it a viable therapeutic option. At 100 μg/mL, ZnO:9Ag reduced cell viability in 50% of strains, notably in L. interrogans, L. kirschneri, and L. noguchii species. ZnO:9Ag induced a significant permeability change (p<0.05) and substantial intracellular content extravasation across all species. The checkerboard method revealed a significant synergistic antibacterial effect of the ZnO:9Ag combination with doxycycline, penicillin G, streptomycin, and tetracycline against the L. interrogans species. In vivo, ZnO:9Ag differed significantly (p<0.05) from the negative control in the GGT enzyme parameter. In conclusion, ZnO:9Ag shows promising potential as an alternative antibacterial agent against Leptospira spp., inhibiting growth with a relatively safe and low toxicity level.