Evaluation of the antimicrobial activity of Cinnamomum zeylanicum essential oil and trans-Cinnamaldehyde against resistant Mycobacterium tuberculosis

The essential oil (EO) extracted from the bark of Cinnamomum zeylanicum (Czey; also known as cinnamon), mostly derives its properties from its major compound trans-cinnamaldehyde (TCin). The present study evaluated the antimycobacterial activity of the essential oil from Czey (CzeyEO) and TCin against sensitive and resistant clinical isolates of Mycobacterium tuberculosis, as well as the combinatorial effects of CzeyEO and TCin with the anti-tuberculosis (TB) drugs rifampicin (RIF) and isoniazid (INH). The resazurin microtiter assay method was used to determine the minimum inhibitory concentration (MIC) of the components tested on the clinical isolates of M. tuberculosis. The effects of the CzeyEO/RIF, CzeyEO/INH, TCin/RIF, and TCin/INH combinations on the M. tuberculosis H37Rv reference strain were evaluated using the checkerboard method to determine the fractional inhibitory concentration index (FICI). CzeyEO and TCin inhibited all bacterial clinical isolates. In the interactive experiment, CzeyEO and TCin were found to be highly effective in reducing the resistance of resistant M. tuberculosis to RIF and INH. All four tested combinations demonstrated synergistic and additive effects, with no antagonistic effects. The synergistic combinations of CzeyEO/RIF and CzeyEO/INH exhibited FICI values of 0.375 and 0.5, respectively, while the TCin/RIF and TCin/INH combinations exhibited FICI values of 0.31 and 0.5, respectively. These results indicate that CzeyEO and TCin are potential candidates for the treatment of drug-resistant tuberculosis in combination therapy with INH and RIF