Bacteriostasis and safety evaluation of two lactic acid bacteria

In this study, two strains of lactic acid bacteria Lactobacillus casei (S60) and L. plantarum (S72) were tested by aseptic technique, including routine biochemical detection, susceptibility test, in vitro bacteriostasis test and animal experiment. Their feasibility and safety as probiotics for fishing were also verified. Results show that the two lactic acid bacteria could tolerate acid (pH 4.0) and bile salt (0.1%), and exhibit different antibacterial activities against six pathogens including Aeromonas hydrophila. The results of antimicrobial substances analysis shows that the effective antimicrobial substances were related to the organic acids produced in metabolic process. The results of safety evaluation shows that the two strains of lactic acid bacteria had no ability to decompose gelatin and hemolysis. The results of death statistics and blood biochemical indicators show that the intraperitoneal injection of live bacteria as high as 1.0×10⁹ CFU·mL⁻¹ did not cause serious death and body injury in experimental fish. It is included that the two strains of lactic acid bacteria have high safety as oral probiotics. Drug resistance studies show that the two strains of lactic acid bacteria had strong tolerance to aminoglycosides and sulfamethoxazole, and were sensitive to ampicillin, enrofloxacin, florfenicol and doxycycline. Therefore, the application of the two strains of lactic acid bacteria should pay attention to the selection of drugs in management process.