Abstract/Summary

Poultry provides an important protein source consumed globally by human population. Simultaneously poultry act as a substantial reservoir of antibiotic resistant Escherichia coli (E. coli) strains including commensal with beneficial roles on poultry health and productivity, and pathogenic not only to poultry but zoonotically to man. This study investigated the role of phytochemicals as possible alternatives to antibiotics and natural anti-bacterial agents to control E. coli; carvacrol oil (the active ingredient of oregano) and oregano oil. The possible anti-E. coli roles of these phytochemicals were associated with missense mutations in marR and cadC genes, mutations in acrA and TolC genes and in ampC, ampH, pbpC and pbpG genes, which are bacterial strategies to overcome antibiotics. A total of 31 representative E. coli strains from 3 different sources of poultry (12 APEC strains, 9 commensal chicken strains, and 10 commensal turkey strains) were shown to be phenotypically and genotypically diverse, and sequentially differentiating between types proved to be difficult. These phytochemicals inhibited the growth and biofilm formation at very low concentrations (MIC values ranging between 0.2 - 0.5µg/ml) in comparison with antibiotics. At sub-MIC levels, these phytochemicals did not induce metabolic changes (SCFAs production) in the E. coli strains, but synergistic interactions between carvacrol and ampicillin were observed in controlling the most ampicillin-resistant E. coli strains. Though, when this combination therapy was investigated using batch culture with chicken caecal content challenged with an ampicillin-resistant APEC strain, it showed an adverse effect. Carvacrol treatment showed positive impact on the bacterial population by enhancing the growth of probiotic bacteria (Lactobacillus sp. and Lactobacillus salivarius) and bacteria with anti-Salmonella activity (Streptococcus sp. and Coprococcus sp.). Thus, providing evidence that carvacrol as a feed additive might enhance avian gut health by controlling antibiotic-resistant APEC strains, but this needs to be supported by in vivo studies.