Secondary metabolites of marine-derived Bacillus spizizenii against the enteric redmouth disease in common carp, Cyprinus carpio

Looking for effective alternatives, such as secondary microbial metabolites, is needed to restrict the use of antibiotics in farmed fish and their detrimental effects on public health and the environment. Thirty-three water and sediments samples were collected from coastal areas in the Basrah Governorate, southern Iraq, to assess their biological activity against bacterial pathogens isolated from Cyprinus carpio, with enteric red mouth disease. 20 spore-forming bacteria were isolated and identified by VITEK BCL cards and amplifying the gyrA gene. Furthermore, the secondary metabolites produced by the strains were extracted and analyzed by GC-MS. Four pathogenic bacteria were isolated from common carp infected with the enteric red mouth disease. The antibacterial activity of the extracts of the isolated marine strains was examined on bacteria causing enteric red mouth disease and Y. ruckeri and P. aeruginosa. Based on the results, the marine isolates were identified as B. spizizenii and GC-MS analysis revealed that these strains' extract contained amino acids and their derivatives and esters and hydrocarbons. Also, biochemical identifications showed that the bacteria isolated from fish belonged to the species of Yersinia ruckeri, Aeromonas hydrophila, Streptococcus agalactiae, and Pseudomonas aeruginosa. According to the antibacterial activity assay, the extracts of B. spizizenii strains were considerably active against bacteria involved in enteric red mouth disease, especially Y. ruckeri. These findings indicate marine B. spizizenii can be replaced with antibiotics in the aquaculture industry to combat infections.