Bacteria of genus Bacillus as antagonists of pathogens in aquaculture

Abstract

Due to the increasing resistance of aquaculture pathogens to antibiotics, the search for new approaches to the control of infectious diseases is of particular importance. A promising approach is the development of probiotic preparations based on antagonist bacteria. The paper studied the antagonistic activity of Bacillus strains that are promising for developing probiotics for fish. The strains were isolated from the bottom sediments of the Don River in the area of the Donskoy Fish Reserve, as well as from the intestines of cyprinids of natural populations, namely, from silver carp (Cyprinus gibelio), roach (Rutilus heckelii), and bream (Abramis brama). The inhibitory effect of Bacillus strains against causative agents of aeromonosis, pseudomonosis and bacterial hemorrhagic septicemia was studied by the method of delayed antagonism. Aeromonas and Pseudomonas species pathogenic for fish were isolated from sturgeons, cyprinids and salmons grown in pond farms and recirculating aquaculture systems in the Krasnodar Region, Rostov Region and the Republic of Adygea. It has been shown that sensitivity to the action of bacilli is not only a species, but also a strain-specific trait among bacterial pathogens of fish. Five strains were identified that exhibited the maximum antagonistic activity against the studied pathogens, and their species identification was carried out by molecular biological and mass spectrometric methods. It has been established that the most pronounced antagonism is exhibited by strains of bacilli isolated from bottom sediments. The growth of all studied strains of fish pathogenic species of Pseudomonas was suppressed only the B. subtilis R4 strain. Thus, strains of aerobic spore-forming bacteria suitable for the creation of probiotic preparations for aquaculture objects have been isolated and characterized.