Occurrence of infectious Streptococcus agalactiae in the farmed Nile tilapia | ||||
| Egyptian Journal of Aquatic Biology and Fisheries | ||||
| Article 24, Volume 26, Issue 3, May and June 2022, Page 403-432 PDF (1.06 MB) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/ejabf.2022.243162 | ||||
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| Author | ||||
| Ahmed H. Sherif et al. | ||||
| Abstract | ||||
| This study examined the Nile tilapia (Oreochromis niloticus) to determine the presence of Streptococcus agalactiae bacteria in three different sites. Isolates were identified, and gene sequences revealed four strains (accession numbers OL471406, OL471407, OL471408, and OL470978). The four strains harbored different virulence genes, and the most virulent strain was used in the treatment trial. The antibiotic of choice was florfenicol (FFC) for the isolate (minimum inhibitory concentration, 12 µg/g body weight, b.w.) and the median lethal dose of S. agalactiae was determined to be 0.3 × 105 CFU/mL. Experimental infection propagated the same clinical signs and post-mortem close to those obtained in the natural infection. Spirulina platensis at a concentration of 5 g/kg b.w. ameliorated the impact of FFC (12 and 1200 µg/k b.w.). A high dose of FFC could minimize the presence of carrier fish, but with deleterious effects on the immunity, which could be boosted by dietary S. platensis. Therefore, S. agalactiae could be confirmed to be associated with a high isolation rate in freshwater fish farms. A 100-fold of the minimum inhibitory concentration (MIC) in FFC could eliminate carriers and minimize coherent infection; thus, the addition of S. platensis to the medicated diet of O. niloticus is recommended to enhance the therapeutic efficacy by improving the immune responses of fish. | ||||
| Keywords | ||||
| Oreochromis niloticus; Streptococcus agalactiae; isolation rate; florfenicol; Spirulina platensis | ||||
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