Currently, in Kazakhstan, chemical agents and antibiotics are widely used for treatment and prevention of fish diseases at fish farms. The use of probiotics as an alternative to antibiotics can help reduce the spread of antibiotic resistance in this area. The aim of the present study was to isolate the intestinal lactic acid bacteria of wintering carps. We assume that such bacteria can have more adaptive properties and can be used as probiotics for growing carp juveniles at fish farms. A probiotic characteristic of 22 lactic acid bacteria isolated from Common carp intestines was studied. Universal primers were used to determine the sequence of 16S rRNA gene fragments of lactic acid bacteria (LAB). Phylogenetic relationships of the isolates were estimated using the neighbor-joining (NJ) method in Mega 6,0. All identified isolates can grow in temperature range from 10° C to 37° C and in presence of bile salt. The isolated bacteria were screened for antibacterial activity, resistance to bile, resistance to antibiotics and growth at low temperatures. All isolates were tested in vitro for their ability to inhibit the growth of Shewanella xiamenensis, Pseudomonas taiwanensis, Ps. aeruginosa and Aeromonas punctata. As a result, 7 isolates with strong antagonistic activity were selected. 16S rDNA gene sequencing identified 4 isolates as Lactobacillus fermentum, 2 - as L. casei/paracasei and 1 - as Pediococcus pentosaceus. Antibiotic resistance profile of selected strains was studied, too. This study is the first attempt for Kazakhstan to isolate and study the representatives of the normal intestinal microflora of commercial fish species. Selective strains could be potential probiotics for freshwater aquaculture practices in Kazakhstan.
The biological variety of aquatic ecosystems is significantly impacted by the chemical and microbiological composition of water bodies, and there is strong reciprocal feedback between these two factors, especially for reservoirs, which can and do have a significant impact on neighboring ecosystems. Today there is an acute need to identify the most effective and economically feasible methods for cleaning and restoring water bodies. Therefore, the aim of the study was to find strains of microorganisms which are capable of biodegrading such problematic pollutants as insoluble phosphates and excess nitrogenous compounds and at the same time, are capable of suppressing the bacterial composition in reservoir waters. In the course of the research, a number of the most active strains of microorganisms were isolated from lake water samples. Five isolates were obtained from salt water and the isolates were then identified using morphological, and biochemical techniques, as well as the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). In addition to the characterization and identification of the isolates, the species-specific levels of phosphate solubilizing, and nitrifying activities were also established. Thus, all isolated strains were studied and characterized, and their influence on the content of minerals such as phosphorus and nitrogen, which are important for living organisms in water, was studied. In summary, the Pseudomonas Extrem-Orientalis isolate was observed to be highly effective in solubilizing phosphates, nitrifying, and had the greatest antagonistic capacity among the investigated isolates. The information gleaned from the study’s findings helps raise more awareness in the field of microbiology and water treatment in general. The findings offer promise for the development of biopreparations with bioremediation capabilities for cleaning polluted water bodies of pollutants from various sources.
The article focuses on a simulation of a bacterial infection of fingerlings carried out in laboratory conditions in order to determine the effectiveness of the developed probiotic. The conditionally pathogenic strains of the genera Pseudomonas and Aeromonas have acted as an infectious agent. Carp fry were used as the test material for disease modeling and studying the effectiveness of a biological product developed for the prevention and treatment of bacterial diseases of fish. The experiment involved two experimental groups and the control one. The probiotic was given to the first experimental group as a feed additive before and after infection; the probiotic was not given to the second experimental group. Species in the control group were not infected and a biological product was not given. Attempts to infect carp fry with an association of strains Pseudomonas taiwanensis , Pseudomonas aeruginosa did not produce any results: after a 2-week period no deviations in the behavior of the fish were recorded, and no fish were killed. Such a situation could be caused by low pathogenicity or by the absence of pathogenicity in museum conditionally pathogenic strains. In the next experiment there was used a more aggressive strain Aeromonas punctata known as the causative agent of fish aeromonosis. Already on the third day after infecting with the pathogen Aeromonas punctata , fish in the second experimental group were killed, and deviations were observed in the form of low mobility of fish and spinal disorders of the type of twisting, which is a consequence of developing bacteriosis - aeromonosis. In fish of the first experimental group that received the previous dose of probiotic no violations were noted, all the fry remained alive. Thus, the therapeutic effect of the developed probiotic was proved on the aeromonosis model, which was expressed in a decrease in the total fish mortality by 27%.
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