Study On The Probiotic Properties Of Intestinal Lactic Acid Bacteria In Tilapia

Whether in China or the word,fish farming is an important part in aquaculture.In recent years,with the expansion of high-density farming,the disease resistance of fish has decreased,resulting in a variety of fish diseases,causing huge economic losses in the aquaculture.Therefore,research and development of microecological preparations with effects of promoting growth,enhancing immunity and improving disease resistance have become a focus.Lactic acid bacteria are gram-positive bacteria that can produce large amounts of lactic acid by fermentation with carbohydrates.Lactic acid bacteria have a variety of probiotic effects.The antibacterial activity of lactic acid bacteria are essential for the health of the intestinal tract of animals.Lactic acid bacteria can inhibit the growth of harmful microorganisms and regulate the balance of microflora in the intestines.In this paper,the lactic acid bacteria isolated from the intestines of tilapia were analyzed for their ability to inhibit pathogenic bacteria,and their antibacterial active substances and biological characteristics were also studied.Aiming at the oxidation problem of aquatic product processing,the antioxidant activity of fish-derived lactic acid bacteria was evaluated.Hope that lactic acid bacteria will play a role in the development and application of natural antioxidants.Agar perforation diffusion method was used to determine and analyze antibacterial activity of 20 strains of lactic acid bacteria(16 strains of Lactobacillus plantarum,3 strains of Lactobacillus pentosus,and 1 strain of Pediococcus citrate)on 5 indicator bacteria(Escherichia coli,Vibrio parahaemolyticus,Staphylococcus aureus,Salmonella,Aeromonas hydrophila).The results showed that there were some differences in the antibacterial ability between the strains,but most of the strains showed better antibacterial activity.The growthand antibacterial properties of 2 strains of lactic acid bacteria in single culture and mixed culture were compared.It suggested that there was no significant difference in growth characteristics between the two culture methods.However,the acid production ability of mixed lactic acid bacteria is stronger than single culture after fermentation.The diameter of the inhibition zone of mixed culture was significantly higher than the single culture.10 strains of lactic acid strains with good antibacterial ability were selected from the above experiments.The effects of hydrogen peroxide,protease,pH and temperature on their antibacterial were tested,in order to detect the properties of bacteriostatic active substances.Results showed that hydrogen peroxide were produced in the culture supernatant of lactic acid bacteria,and they were sensitive to proteases,showing good heat stability under certain conditions.Their antibacterial abilities were affected by pH.The results indicate that the antibacterial effect of the lactic acid bacteria supernatant may be due to one or a combination of these factors such as bacteriocin,protease,hydrogen peroxide,organic acid or environmental pH.Analysis of acid-tolerant and bile-tolerant ability of 10 strains of lactic acid strains showed that the viability of the strains remained between 62%-81% after culturing for 4 hours at pH 3.0.Moreover,the survival rate of most strains were about 50%,after 4 hours of incubation at pH 2.0,and individual strains lost their survival.The strains showed good tolerance to bile salts,but the survival rate of strains gradually decrease with the increase of the culture time.The results of the test for the drug sensitivity of 13 kinds of antibiotics found that strains were resistant to aminoglycosides,glycopeptides and fluoroquinolone antibiotics,and sensitive to tetracyclines,penicillins,erythromycin and chloramphenicol.Lactic acid bacteria sensitive antibiotics should be avoided as much as possible during aquaculture.The supernatant,bacterial suspension and cell-free extracts of 10 strains were measured the scavenging ability of hydroxyl radicals,superoxide anion radicals and DPPH free radicals.The scavenging ability of 10 strains of lactic acid bacteria to several free radicals were supernatant,bacterial suspension,cell-free extracts,from strong to weak.In particular,cell-free extracts had little or no ability to scavenge several free radicals.The clearance rate ofhydroxyl radicals in the supernatant were above 10%.The clearance of DPPH free radicals rate were over 50%.The supernatant had scavenging rate of superoxide anion radicals above20%.The clearance rate of hydroxyl radicals in suspension of 10 lactic acid bacteria were quite different,ranging from 5.34% to 32.02%.The scavenging rate of DPPH free radicals by the suspension were between 14.28% and 28.55%;the scavenging rate of superoxide radicals were between 9.11% and 13.68%.Only the culture supernatant had good reducing ability,and neither the suspension nor the cell-free extract detected reductive properties.