Probiotic Bifidobacterium lactis HN019 enhances the resistance and immunity against enteric pathogens : a thesis presented in partial fulfilment of the requirements for masters degree in nutritional science at Massey University
Probiotics are defined as a group of live microorganisms, including some microbial stimulants that exert health promoting effects, such as the maintenance of a normal intestinal microbiotia, increased nutritional value of foods, anticarcinogenic activity, reduction of serum cholesterol levels, alleviation of lactose intolerance and stimulation of the immune system. Some of strains of lactic acid bacteria (LAB) are representative probiotics. The objective of this study was to examine the immunomodulatory and antiinfection properties of a new identified LAB strain- Bifidobacterium lactis using two animal models. Two experiments were conducted and reported in this thesis. In the first experiment, a piglet weaning diarrhoea model was used to test the efficacy of Bifidobacterium lactis HN019 protecting against diarrhoea associated with Rotavirus and E. coli. 17 three-week-old piglets were allocated into two groups balanced for liveweight and litter of origin. The first group (n=8) was orally administered B. lactis HN019 (109 cfu/piglet/day) through the experiment; the second group (n=9) was not given B. lactis HN019 (control). After one week, the animals were penned individually and weaned onto a weaner diet. Blood samples were taken to measure the antibody responses, cell proliferation, and phagocytic activity of leukocytes (monocytes and neutrocytes). Also the effect of B. lactis HN019 on weaning diarrhoea was assessed by monitoring the severity of diarrhoea, feed intake and liveweight gain of the piglets on the weaner diet. Compared to the controls, piglets receiving B. lactis HN019 had lower severity of weaning diarrhoea, higher survival rate and feed conversion efficiency (or liveweight gain). The protection was associated with lower levels of faecal rotavirus and E. coli shedding, higher phagocytie activities and cell proliferative response to mitogens, and higher specific antibody titers. These results suggest that dietary B. lactis can reduce the severity of weaning diarrhoea associated with rotavirus and E. coli, and the probiotic is associated with enhanced immune responsiveness. In the second experiment, the protective effects of Bifidobacterium lactis HN019 against E. coli O157:H7 and associated immunological parameters were investigated using murine models. After one week acclimatisation on a skim milk powder (SMP)-based diet, eighty-six BALB/c and C57 mice were selected and randomised to two treatment groups. One group was fed on the SMP-based diet until the end of the experiment, while the other group was fed the SMP-based diet supplemented with B. lactis HN019 (3 x 108 cfu/g). After one week on these diets, mice were intragastrically inoculated with 0.1 ml E. coli O157:H7 suspension (109 cfu/ml). Protection against E. coli O157:H7 infection was assessed by monitoring the morbidity, feed intake, bacterial translocation to visceral tissues (spleen and liver) and immune responsiveness. Phagocytic activities of blood and peritoneal cells, and antibody titres against E. coli O157:H7 in intestinal content were also measured. The results showed that B. lactis HN019-fed mice conferred a significant degree of protection against E. coli O157:H7 challenge in comparison to the control mice that did not receive B. lactis HN019. Protection included lower morbidity and higher post-challenge feed intake, reduced pathogen translocation to blood, spleen and liver, as well as significantly higher phagocytic activities of blood and peritoneal cells and anti-E. coli IgA level in gut content. These results suggest that B. lactis HN019 can enhance the host resistance to E. coli O157:H7 and that the protection is associated with enhanced immune functions. In summary, potential immune enhancing effects of B. lactis HN019 were investigated in one pig trial and one mice trial. The results showed that supplement of B. lactis HN019 relieved diarrhoea associated with rotavirus and E. coli infection in piglets and enhance the host resistance to E. coli Ol57:117 challenge in mice. Immunological measurements indicated B. lactis HN019 fed groups had significant higher phagocytosis and anti-E. coli IgA levels. And the pathogen shedding was also reduced in B. lactis HN019 fed groups. As concluded, B. lactis HN019 can provide a protective role against special enteric pathogen infection by its immunomodulatory effects.