Sub-lethal Concentrations of Phytochemicals (Carvacrol and Oregano) Select for Reduced Susceptibility Mutants of Escherichia coli O23:H52

In vitro studies aimed at studying the mechanism of action of carvacrol and oregano as natural anti-bacterial agents to control multiple antibiotic-resistant avian pathogenic Escherichia coli (APEC) strain O23:H52 isolated from chicken were performed. Derivatives with increased minimum inhibitory concentrations (MIC) to the phytochemicals were selected after growing Escherichia coli (E. coli) strain O23:H52 at sub-lethal concentrations of carvacrol and oregano for a period of 60 days. Whole-genome sequencing (WGS) of two derivatives revealed a missense mutation in cadC and marR: the genes responsible for survival mechanisms and antibiotic resistance by efflux, respectively.