Abstract/Summary

Avian pathogenic Escherichia coli (APEC) and commensal E. coli are often found in the intestinal tract of poultry. APEC can cause several types of disease manifesting at various developmental stages in the life cycle of poultry. The goals of this study were to investigate the relationship between APEC and commensal E. coli, and to elucidate whether specific dietary components such as plant extracts (thymol and carvacrol) may be implemented to control APEC. Genotypic and phenotypic diversities were estimated in 200 E. coli isolates from poultry of which 100 were from healthy turkey, 35 from healthy chicken, and 65 APEC strains were isolated from infected chicken. The genetic data indicated high diversity among E. coli isolates whereas phenotypic diversity association with pathogenicity was unclear. The antimicrobial activity of thymol and carvacrol against E. coli had a significant impact on reducing bacterial growth, biofilm formation, and motility. Moreover, thymol reduced conjugation, and induced morphological changes in E. coli. An E. coli strain was adapted to tolerate high concentration of thymol, and its metabolic profile detected by NMR analysis showed slowed growth with a shift from respiration to fermentation as indicated by increasing lactate and pyruvate family amino acids. Genome sequencing of the tolerant strain showed a mutation in the acrR gene encoding a suppressor of the AcrAB-TolC efflux pump suggesting that overactivation of the AcrAB efflux pump increased thymol clearance. The impact of thymol on the composition and activity of caecal microbiota was assessed by in-vitro batch culture. 16S rRNA sequences were used to identify caecal microbiota and metabolic profiles were characterised by 1H-NMR spectroscopy. Thymol was associated with increases in lactic acid and a growth shift favouring commensal gut bacteria. In conclusion, supplementation with thymol may exert a positive effect on intestinal microbiota if used invivo.