关键词: 乳酸菌, 牛呼吸系统疾病, 生理特性, 抑菌活性

Abstract: [Objective] By studying the physiological properties and bacteriostatic activities of bovine-derived lactic acid bacteria, it was possible to screen lactic acid bacteria that can have bacteriostatic effects on Pasteurella multocida （Pm） and Mannheimia haemolytica （Mh）, the main pathogens that lead to respiratory diseases in cattle. [Method] Growth curves of Lactobacillus rhamnosus （Lr）, Lactobacillus plantarum （Lp） and Lactobacillus acidophilus （La） isolated from healthy cattle faeces were performed. Meanwhile, the bacteriostatic activities of the three Lactobacillus strains were evaluated by detecting their susceptibility to antimicrobial drugs in the presence of proteases, at different pH values, and in co-culture with Pm and Mh. [Result] All three strains of Lactobacillus entered the logarithmic growth phase after 6 h of incubation, with Lr and Lp growing faster. They entered the stable growth period after 20 h of incubation, and the viable counts of Lr and Lp were always higher than those of La throughout the growth process. In addition, all three Lactobacillus strains were resistant to levofloxacin, moderately sensitive to kanamycin and streptomycin, and sensitive to ampicillin and erythromycin. Compared to the control, the culture supernatant of Lr showed a small decrease in the inhibitory activity against Pm and Mh after reaction with trypsin, pepsin and proteinase K. The culture supernatant of Lp showed no reduction in the inhibitory activity against Pm and Mh after reaction with pepsin and no change in the inhibitory activity against Mh after reaction with trypsin. There was no decrease in the inhibitory activity against Pm after reaction of culture supernatant of La with trypsin, pepsin and proteinase K. There was no change in the inhibitory activity against Mh after reaction with proteinase K. When the pH was 2-3, the inhibitory activities of culture supernatants of Lr and Lp were stronger on Pm than the control, and the inhibitory activities of culture supernatants of La were stronger on Mh than the control. When the pH was 4, the inhibitory activity of culture supernatants of all three strains of Lactobacillus was weaker than that of the control against Mh. When the pH was 5-6, the inhibitory activities of culture supernatants of the three Lactobacillus strains were weaker than those of the control group for both Pm and Mh, as well as weaker than those of the other pH groups. The growth of Pm and Mh was inhibited by the culture supernatants of the three Lactobacillus strains during the co-cultivation period from 0 to 60 h. The growth inhibition of Pm by the culture supernatant of Lr was consistently better than that of Lp and La. The growth inhibition of Mh by the culture supernatant of La was the most effective. [Conclusion] Bovine-derived Lr, Lp and La were sensitive or moderately sensitive to a variety of antimicrobial drugs, and had growth inhibitory abilities against Pm and Mh, the main pathogens of BRD. The inhibitory activities were enhanced at low pH and were not affected by the action of specific species of proteases. The three strains of Lactobacillus have the potential to be developed as microecological agents for the prevention and treatment of BRD.

Key words: lactic acid bacteria, bovine respiratory disease, physiological property, bacteriostatic activity