Synergistic Effect of Cinnamomum camphora and Origanum vulgare Essential Oils against bla 𝐶𝑇𝑋-𝑀 Producing Escherichia coli Isolated from Poultry Colibacillosis

Background: The transmission of antibiotic resistance through the food chain is one of the major health challenges, worldwide. A combination of essential oils with synergistic or additive effects to enhance the antimicrobial activity, is an applied approach to improve food safety. Methods: In this study, 93 E. coli isolated from the viscera of broilers, suspected to colibacillosis, were examined for detection of ESBL by the combined disk method according to Clinical and Laboratory Standards Institute. 𝐶𝑇𝑋-𝑀 was detected by PCR. Antibacterial activity of cinnamon and oregano essential oils were studied against bla 𝐶𝑇𝑋-𝑀 harboring isolates by broth microdilution method and fractional inhibitory concentration index. Results: According to the results of this study, 32/93 (34.4%) of tested samples produced ESBL, and 10/32 (31.2%) harbored CTX-M. All the 𝐶𝑇𝑋-𝑀 producing E. coli investigated by broth microdilution assay, were sensitive to cinnamon and oregano essential oils in the range of 400 to 3200 and 800 up to 1600 ppm, respectively. Fractional inhibitory concentration indices ranging from 0.5 to 1.5, suggested synergistic, and additive inhibitory effect of cinnamon and oregano essential oils. Conclusion: The results of this study indicated that bla 𝐶𝑇𝑋-𝑀 might be transmitted to humans through chicken meat. The combination of cinnamon and oregano can be suggested as a safe bio-preservative which leads to growth inhibition of antibiotic resistant E. coli. However, further studies should concern the potential interaction between essential oils and food matrices.