Abstract/Summary

The Prophylactic use of antibiotics in poultry has been banned because of increasing incidence of antibiotic resistant bacteria. Therefore, probiotics are being developed as alternatives to control pathogenic bacteria in poultry. The aim of this research was to isolate yeast from chicken and to test for their probiotic potential. Various yeast strains were isolated from the chicken environment and gut and identified based on their phenotypic metabolic characteristics. Their probiotic potential was assessed by studying the physical and chemical reactions between yeast cells and Avian pathogenic Escherichia coli (APEC) strains. The components of the yeast supernatant that could be responsible for suppressing APEC growth were measured using gas chromatography and proton nuclear magnetic resonance spectroscopy. The safety of the yeast probiotic candidate was assessed in vitro by cytotoxicity assays using HT-29 tissue culture. The effect of feeding chickens with yeast on their caecal E. coli population and the pathogenicity of those coliform was studied using cultural and PCR based methods. In vitro experiments showed that Candida famata was the yeast isolate that suppressed growth of APEC to the greatest degree by causing agglutination, producing antimicrobial compounds and interfering with the adhesion and invasion of host cells. C. famata was found to be not toxic to intestinal cells, therefore live cultures of this yeast were administered to the drinking water of chickens. The in vivo experiment showed that caecal E. coli population density and the expression of virulence genes were not significantly affected by the presence of C. famata. The conclusion of these studies is that C. famata has probiotic potential in vitro but this was not reflected in vivo due to insufficient dosing and poor colonization of the yeast. Also, the complexity of the avian gut and the diversity of its microbiome are factors which are not easy to control.