Antibacterial activity of essential oils for combating colistin-resistant bacteria

ABSTRACT

Objectives

Colistin (polymyxin E) is a bactericidal antibiotic used to treat severe infections caused by multidrug-resistant Gram-negative bacteria. The product of the mcr1 gene generates transferable plasmid-mediated colistin resistance, which has arisen as a worldwide health-care problem. This study aimed to isolate and identify colistin-resistant bacteria, and evaluate the ability of essential oils in its fights.

Methods

Twenty-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.

Results

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.

Conclusions

Cinnamon oil exhibits antibacterial activity against colistin-resistant strains, showing it as a promising natural alternative in clinical therapy.

KEYWORDS:

• Cinnamon oil
• colistin-resistant bacteria
• mcr-1 gene
• GC-MS
• cytotoxicity

Article highlights

• Colistin resistance was found in a high relative percentage of bacteria isolated from cancer patients.

• Cinnamon oil is enriched in cinnamaldehyde and its derivatives, which have antibacterial properties.

• Cinnamon oil downregulates the mcr-1 gene in colistin-resistant isolates of P. mirabilis and E. coli.

• Cinnamon oil can fight natural or acquired colistin resistance in Gram-negative bacteria

Declaration of interests

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Author contributions statement

G.M.E., S.A.M., and M.H.K. conceived of the presented idea and developed the design of experiments. A.M.F., M.H.K., and E.M.E. performed the methodology and verified the analytical methods. G.M.E. and S.A.M. supervised the findings of this work. All authors discussed the results, wrote, and contributed to the final manuscript.

Ethical approval

Ethical approval and informed consent were not required for this study