Abstract/Summary

Colonisation of birds by Brachyspira pilosicoli can result in avian intestinal spyrochetosis (AIS). AIS is associated with weight loss, decrease egg production and animal death. This disease is an increased burden worldwide and results in important economic losses. Tiamulin TM, an antibiotic of the pleuromutilin family is the most common and efficient way to treat AIS. However, it is badly used in farm due to absence of indications regarding the dose to be used in chickens. Furthermore, B. pilosicoli is becoming increasingly resistant to treatments. This work focused on the NMR-based metabonomics evaluation of AIS by studying the pathogen, the host and their reaction to Tiamulin TM treatment. Work was divided up as follow: 1. B. pilosicoli metabolism in optimum growth condition and after Tiamulin TM treatment was determined by evaluating metabolic composition of the medium throughout 120h growth using 1H-NMR. Tiamulin appeared to be able to reduce B. pilosicoli growth by 1 log at 0.008 and 0.016 μg/ml. Highest concentrations inhibited bacterial growth. However, B. pilosicoli was still metabolically active up to the 0.250 μg/ml dose. These results indicate that bacteria, even if not able to divide due to antibiotic treatment, remain alive explaining re-occurrence of the disease in farms post-antibiotic treatment. 2. Host metabolism was explored using 1H-NMR techniques. Metabolic composition of twelve matrixes (liver, kidney, spleen, plasma, egg, breast muscle, cortex, ileum, caecum, colon and faeces) were characterised and grouped as a metabolic atlas to be used as a database for future avian research. 3. An animal trial evaluating the impact of Tiamulin TM treatment on infection and symptoms was conducted. This also allowed determination of the best dose to be used in farmyard applications. Infection was systemic and mainly associated to diarrhoea and decreased growth rate. All antibiotic doses were able to significantly reduce percentage of infected birds and infection spread in the organism while only the two highest doses re-established growth rate and increased egg production (previously unaffected by infection). Results indicate that 125 ppm of tiamulin was sufficient to efficiently treat chickens while avoiding associated economical loss. 4. Metabolic and caecal microbiota composition response to infection and antibiotic treatment were evaluated using tissues and biofluids sampled from the animal trial described in 3. Infection by B. pilosicoli was associated with dysbiosis and modification of energy metabolism characterised by lipolysis to maintain plasma glucose levels. Tiamulin treatment also induced dysbiosis. Even if treatment was able to cancel metabolic response to infection, Tiamulin TM strongly disturbed cholesterol metabolism in a dose dependent manner. Treatment induced a decrease of the HDL/VLDL ratio and made birds age faster than untreated ones. Steroid hormonal disturbance was explored as potential cause of the cholesterol metabolism perturbation. In conclusion, this work contributed significantly to increase B. pilosicoli induced AIS general understanding. It also enlightened metabolic mechanism responsible for symptom development and finally showed that antibiotics may strongly influence metabolism.