The camelliagenin from defatted seeds of Camellia oleifera as antibiotic substitute to treat chicken against infection of Escherichia coli and Staphylococcus aureus

Background: Escherichia coli and Staphylococcus aureus are the main pathogens infectious to poultry, and their resistances against antibiotics have become troublesome currently. Biofilm formation is an important reason for drug resistance. Our previous research has found that the extract of Camellia oleifera seeds has lots of pharmacological effects. In order to find the substitute for antibiotics, the saponin was isolated from the defatted C. oleifera seeds with structural identification. Its efficacy was evaluated by the inhibition on amoxicillin-resistant E. coli and erythromycin-resistant S. aureus and therapeutic effect on chicks infected by the two bacteria. Results: The bacterial growth inhibition rate increased and the bacterial count in vivo decreased significantly in dose dependence after administration of the saponin and its combination with amoxicillin or erythromycin, suggesting its antibacterial effect. The saponin identified as camelliagenin shows significant inhibition on the biofilm of E. coli and S. aureus, and it is related to the decrease of mannitol dehydrogenase (MDH) activity and extracellular DNA (eDNA) content. Molecular simulation reveals the strong interaction existing between the saponin and MDH or eDNA. Conclusions: The mechanism of camelliagenin's improvement on antibiotic effects is its interaction with MDH and eDNA in biofilm. The saponin is a prospective substitute of antibiotics, and molecular simulation is a convenient alternative method to find out hopeful candidates of antibiotics substitute.