Streptococcus iniae is an important pathogen that can cause a broad range of disease in aquatic animals. To avoid the use of antibiotics and drugs, it is critical to identify protective antigens for developing highly effective vaccines against this pathogen. Vaccination is the most effective means of preventing infectious diseases; however, few vaccines are effective against Streptococcus iniae (S. iniae) in monosex Nile Tilapia. This work presents an efficacious and safe vaccine against S. iniae infections in monosex Nile tilapia (Oreochromis niloticus). The vaccine candidate S. iniae F-1 strain administered by intraperitoneal (i.p.) injection, and consisted of inactivated antigens; both the vaccinated and nonvaccinated fishes were challenged intraperitoneally with S. iniae (1 × 10 7 CFU ml −1 ) isolates and PBS (negative control). Peripheral blood samples were collected for SDS-PAGE, phagocytosis and agglutination assays. Present results indicated that immunoglobulin M (IgM) was maximally expressed in the low-amperage electric current inactivated (ECKC) vaccinated group at 3 months post-secondary vaccination (PSV). Phagocytic activity and index increased significantly in (ECKC) vaccinated group. Furthermore, fish in (ECKC) vaccinated group exhibited significantly elevated agglutination titers compared to fish in the control group, in which almost no agglutination reaction was detected. In the efficacy test, the vaccinated fishes had a significant increase in RPS (69 and 89, respectively); the percentage mortality declined from 83 ± 0.6 and 74 ± 0.7 in challenged and control fishes to 25% ± 0.8% and 8% ± 0.8% in vaccinated and challenged fish groups, respectively. Furthermore, the level of protection observed in the field trial closely resembled that achieved on a laboratory scale. Therefore, EC-killed showed the highest molecular weight 31 kDa in SDS-PAGE and Western blot and increased RPS (91%), suggested that the EC-killed cells of S. iniae could play an important role in immunizing mono-sex Nile tilapia. The EC-killed cells of S. iniae will may safe and long-lasting protection against streptococcosis.
This study was intended to address, the effect of oxytetracycline, erythromycin, and streptomycin on the antimicrobial resistance of Aeromonas sp. isolated during the production process, from infected common carp (Cyprinous carpio). Antimicrobial resistance patterns were defined by determination of minimal inhibitory concentrations (MIC) of three antimicrobial drugs, and bacteria. Results indicated that In vitro bactericidal activity, oxytetracycline showed lowest number of bacterial colonies (1×10-4 c.f.u./ml) than erythromycin (3×10-4) and streptomycin (4.5×10-4) compared to the control (9×10-4). Oxytetracycline showed the highest maximum zone of inhibition (20 mm) than erythromycin (18 mm) and streptomycin (15 mm) in antibiotic susceptibility test. In infection inhibition assay, serum from oxytetracycline fed diets inhibited Aeromonas infection to common carp. The susceptibility of the fish fed antibiotics (50 µg/mg feed) and challenge with Aeromonas sp. (1×10-4) was examined for 30 days. There was high relative percent of survivility (RPS) in oxytetracycline was 73%. Very low RPS 63% and 47.37% was found in erythromycin and streptomycin against Aeromonas sp. infection. These results demonstrated that the oxytetracycline might be a potential for Aeromonas sp. infection to common carp (Cyprinous carpio).
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