Enhancing Antibacterial Activity by Combination of Chloramphenicol with Constituents from Dracaena cochinchinensis (Lour.) S.C.Chen

Background: Seven compounds were isolated from Dracaena cochinchinensis and elucidated their structure by NMR spectroscopic analysis and determined the optical rotation for certain compounds. Methods: These compounds were screened for antibacterial activity by using agar well diffusion and determination of minimum inhibitory concentration (MIC) was conducted by the broth micro-dilution method using resazurin colorimetric assay. Further investigation on combination effect between each compound with chloramphenicol was conducted by agar well diffusion method. Among the seven compounds, compound 4 displayed the highest antibacterial activity against P. acnes and S. aureus with the inhibition zone of 17.3 and 16.7 mm, respectively. The MIC value of 1 and 4 against all tested bacteria was 62.5 μM, whereas those of other compounds were 62.5-250 μM. The combination of 4 and chloramphenicol exhibited the most synergistic effect against P. acnes with the rate in increasing antibacterial activity of 4 in combination as 1,250 folds. This compound also enhanced the antibacterial activity of chloramphenicol at 50 μM with an inhibition zone of 16.3 mm comparing to its activity alone (8.7 mm). Results & Conclusion: The results revealed compound 4 displayed the highest antibacterial activity alone and in combination with chloramphenicol against P. acnes and S. aureus.