Antibacterial activity of essential oils for combating colistin-resistant bacteria

Colistin (polymyxin E) is a bactericidal antibiotic used to treat severe infections caused by multidrug-resistant Gram-negative bacteria. The product of theTwenty-seven bacterial isolates were collected from patients who were admitted to the National Cancer Institute, Cairo, Egypt, and processed using standard microbiological methods. Essential oils were purchased from AB Chem Company, Egypt, screened for antibacterial, cytotoxic activity, and (GC-MS) analysis.A total of 5 bacterial isolates were resistant to colistin with minimum inhibitory concentration (MIC) ranging from 6.25-200 µg/ml. Cinnamon oil exhibited the highest activity against colistin-resistant strains followed by thyme and eucalyptus oil. The (MIC) of cinnamon oils against resistant strains ranged from 4.88 to 312.5 µg/ml. Moreover, mcr-1 gene expression was extremely down-regulated after the treatment of bacterial strains with cinnamon oil and decreased to 20-35-fold. Examination of treated bacterial cells with sub-inhibitory concentrations under transmission electron microscopy showed various abnormalities occurred in most of these cells.Cinnamon oil exhibits antibacterial activity against colistin-resistant strains, showing it as a promising natural alternative in clinical therapy.