Isolation And Identification Of Lactic Acid Bacteria From The Intestinal Mucous Of Broliers And Preliminary Study On Their Probiotic Role

Six strains of lactic acid bacteria were isolated from intestinal mucous of the broilers and their probiotic roles were investigated by in vitro experiments and in vivo in broilers.The results were described in the following four sections.In the first section, a group of six LAB strains (Rl, R2, R3, R4 R5, R6) were isolated from intestinal mucous of broilers. According to their morphology, and physiological and biochemical characteristics, three strains were identified as belonging to the genus of Lac to bacillus: R2 as Lactobacillus acidophilus, R4 as Lactobacillus delbrueckii subsp. lactic, R6 as Lactobacillus delbrueckii subsp. delbrueckii. Other three strains were identified as Enterococcusfaecalis. R2 and R4 growed more rapidly than the other strains.In the second section, lactic acid production and antagonistic property of the six strains were investigated. The results showed that among all strains, R2 exhibited the most rapid production of lactic acid before 12 h. R4 exhibited the highest production of lactic acid in the culture by 24 h, with the concentration of lactic acid as 69.59mmol L-1. The inhibitory effect of R2 and R4 was more significant than the other strains. When subtracting the effect of the acid, the culture supernatants still showed 10% inhibitory effect, suggesting that their inhibitory effect was mainly caused by lactic acid. The inhibitory effect of the culture supernatant was above 90% after heat treatment or treated with proteases.In the third section, effect of gastrointestinal factors (low pH, bile salt and proteases) on the survival of strains of R2 and R4 were investigated, and the sensitivities of the strains to antibiotics and their adherence to intestinal epithelial cells were determined. The result showed that R2 and R4 could survive well while incubating at pH4 and pH5 for 3h, butcould not survive well when pH was below 3. The two strains did survive well under bile condition. The survival rates of R2 and R4 were 11.17% and 3.31% respectively after incubating in the medium with 0.1% of bile for 10 minutes. There was no significant effect of pepsin and trypsin on the growth of R2 and R4 strains. R2 and R4 exhibited resistance to penicillin, tetracycline, streptomycin, kanamycin and vancomycin. Trypsin significantly inhibited the adherence of R2 and R4 to intestinal epithelial cells.In the fourth section, a crude preparation of live LAB was created to investigate their effect on the growth performance of broilers with corn-based diet. 360 broilers were randomly divided into four groups. Group 1 was supplemented with LAB preparations of strains from intestinal mucous of broilers. Group 2 was supplemented with LAB preparations of strains from intestinal content of broilers. Group 3 was supplemented with LAB preparations of combinations of LAB strains from both intestinal mucous and content. Group 4 was served as the control. Preliminary results showed that the LAB preparations had no significant effect on the broilers' daily weight gain and feed conversion rate. At the age of 42 d, the number of E.coli in jejunum of broilers in all LAB supplemented groups decreased as compared with the control group, with the value in group 3 significantly lower than that in the control. The number of LAB of jejunum of broilers in group 2 and 3 showed a slight increase as compared with the control group.