Antibacterial Synergisms of Ji Xue Teng, Spatholobus suberectus, Extract and Selected Antibiotics against Streptococcus agalactiae from Nile Tilapia, Oreochromis niloticus (L.), In Vitro and In Vivo

Abstract

AbstractStreptococcus agalactiae infection causes severe economic losses in tilapia production. To find out efficacious strategies for curing S. agalactiae infections, this study screened the antibacterial synergisms between Ji Xue Teng, Spatholobus suberectus, extract and selected antibiotics via a modified agar well diffusion method. We optimized a combined ratio of S. suberectus extract and the selected antibiotic, observed their effects on the infections with S. agalactiae on Nile tilapia, Oreochromis niloticus (L.), and determined their antibacterial spectra. The results showed that S. suberectus extract and streptomycin sulfate exhibited antibacterial synergism against S. agalactiae, with an optimal ratio of 42.5:1 (m : m). The minimal inhibitory concentration of S. suberectus extract was reduced from 27.84 to 5.95 mg/mL, and a reduction of streptomycin sulfate from 0.66 to 0.13 mg/mL was noted. After providing infected tilapia, O. niloticus (L.), with feedstuffs containing 0.520% S. suberectus extract only, 0.013% streptomycin sulfate only, or in combination, the relative percent of survival was 52.6, 13.9, and 80.5%, respectively. These results indicate an antibacterial synergism between S. suberectus extract and streptomycin sulfate in vitro and in vivo.