RESEARCH ▶▶▶
similar patterns identified in Europe, Australia and Asia. Due to a lack of understanding of the biology of Brachyspira, to date, interventions and strategies to reduce the incidence of this organism in flocks have been largely unsuccessful and re- cent efforts have primarily focused on researching preventa- tive measures in flocks. A new study of Dr Jade Passey looked into the potential of probiotics to control avian intestinal spi- rochaetosis. Dr Passey is the latest PhD student supported by the British Egg Marketing Board Research & Education Trust, and has just completed her studies at the School of Veteri- nary Medicine at the University of Surrey under the tutorship of Prof. Roberto La Ragione.
Probiotics Preventative measures, such as the use of probiotic bacteria, for example Lactobacillus, are increasing in popularity as they are easily administered to poultry in feed or water supplies. Probiotics work on the principle that when provided in ade- quate quantities, they can confer health benefits on the host and that good gut health can afford some protection from bacteria such as Brachyspira. Therefore, the overarching aim of this PhD project was to investigate Lactobacillus probiotics as an intervention against Brachyspira and to determine the possible mechanisms of Brachyspira inhibition by Lactobacil- lus. This was achieved in several different ways. Firstly, Brach- yspira strains isolated from infected hens in the UK were iden- tified and characterised. Additionally, Lactobacillus strains were isolated from the faeces of healthy laying hens and were also identified and characterised in line with European (EFSA) probiotics guidelines.
Next Stage Once suitable strains of Brachyspira and Lactobacillus were selected, the next stage was to explore the ability of these Lactobacillus strains to inhibit all Brachyspira species known to infect poultry. Several mechanisms of inhibition were in- vestigated such as production of inhibitory metabolites by the Lactobacillus, physical interactions between these bacte- ria and interactions with immune cells both in tissue culture and in an insect infection model. Overall, it was evident that the Lactobacillus strains characterised in these studies were inhibitory against all species of Brachyspira and therefore show promise as potential probiotics. The mechanisms by which they inhibited Brachyspira were multifactorial, and thus it would be important to design a probiotic formulation consisting of multiple Lactobacillus strains.
Lactobacillus reuteri and Lactobacillus salivarius, the most common species of Lactobacillus found in the gastrointesti- nal tract of chickens and used in several probiotic products, were the most promising probiotic candidates of those tested in this study. These strains were able to inhibit Brachyspira in several different ways including: (1) producing inhibitory
metabolites such as lactic acid and bacteriocins, (2) physically interacting with Brachyspira and (3) altering innate immune responses to Brachyspira. Each of these mechanisms are im- portant when considering the inhibition of Brachyspira. First- ly, the production of inhibitory metabolite such as lactic acid is important because lactic acid induces a stress response in Brachyspira due to a lowered pH. This response results in these long, motile bacteria curling into a ball know as a spherical body therefore impairing their motility and ability to adhere and invade the cells of the gastrointestinal tract.
Inhibitory Interestingly, the Lactobacillus isolates that were most inhibi- tory against Brachyspira also utilised the highest concentra- tions of glucose. This could be advantageous in the avian gut because this glucose utilisation would result in lower glucose concentrations for utilisation by pathogenic bacteria such as Brachyspira. Physical interactions between Lactobacillus and Brachyspira also impair the motility of Brachyspira and reduc- es its ability to cause disease. Finally, Lactobacillus were able to alter the immune responses in avian macrophage cells and insect haemocyte cells in response to Brachyspira, which may indicate that Lactobacillus mediates inflammatory responses to reduce the severity of infection in poultry. In conclusion, this project highlights the promise of Lactoba- cillus probiotics as a suitable intervention against the ever- growing health and economic burden associated with Brach- yspira infection. Several mechanisms are associated with Lac- tobacillus inhibition of Brachyspira and therefore, multi-strain probiotic formulations should be further investigated as a potential control strategy for avian intestinal spirochaetosis.
Brachyspira bacteria seen through a microscope. ▶ POULTRY WORLD | No. 4, 2019 33
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