Molecular biological identification and investigation probiotic potential of lactic acid bacteria isolated from freshwater fish in rainbow trout

Aquaculture has become economically important industry in the world. So the purpose of global aquaculture production is to maximize efficiency of cultivation. There is an intensive production in aquaculture to meet the need for increased food in the world so this makes inevitable the emergence of diseases. The occurrence of the disease among the most important factors causing stocks decline. The antibiotics are widely used for control of fish diseases, but they cause spread and develop of resistant pathogens. This case poses a risk such as pass of resistant bacteria from the aquatic environment to the intestinal tract which free of pathogens of people. Therefore, alternative methods have been used in recent years. İn recent years, the lactic acid bacteria has had a significant interest in aquaculture, because most lactic acid bacteria are used as probiotics in the prevention of diseases. In this regard, identification of lactic acid bacteria with good probiotic properties and determination of their probiotic properties are extremely important. Due to the importance of lactic acid bacteria in aquaculture, In the research, phenotypic, biochemical and molecular biological diagnostics of lactic acid bacteria isolated from freshwater fish were performed and then pH tolerance, bile salt tolerance and hydrophobicity ability reflecting probiotic properties were evaluated and from these the best feature of which were intended for use as potential probiotics in rainbow trout. In this research, after phenotypic and molecular determination, antagonistic activity of 75 bacteria strain were investigated. Then the best antagonistic activity of them were analyzed in terms of probiotic properties. In the analysis, the bacteria have the best antagonistic activity against Pseudomonas aeruginosa ATCC 27853, Yersinia ruckerii, Lactococcus garvieae 49156, Escherichia coli O157H7, Salmonella typhimirium 14928 pathogens were F2, F4, F6, F7, F8, F9, F10, F38, F39, F54, F69, 75 (identified as Lactococcus lactis subsp. Lactis) and F14 (identified as Lactococcus lactis). Then the isolates were evaluated in terms of Doxycycline, Enoxacin, Erithromycin, Florfenicol, Trimethoprim, Oxytetracycline, Enrofloxacin, Chloramphenicol, Vancomycin antibiotic susceptibility, pH1 and pH3 tolerance and hidrofobicity ability. from these tests the isolates with the best properties was found as F4. Because of these features the probiotic properties of isolate numbered F4 on rainbow trout were examined. For that the rainbow trout fry were feed without probiotic and with probiotic for 28 day to search and survival rates and effects on body compositions were analysed. At the end of the trial the differences between control and treatment groups in terms of weight gain, relative growth rate, size growth and relative size growth rates were observed. When looking at the survival rate, there was no significant statistical difference. The present research showed that, the feeding with Lactococcus lactis subsp. lactis have positive effect on rainbow trout fry in terms of growth.