Enhancing Effect of Isoeugenol on the Antimicrobial Activity of Isoniazid, 6-Paradol and 6-Shogaol

ABSTRACT The enhancing effect of sub-inhibitory concentrations of eugenol and isoeugenol with isoniazid, 6-paradol and 6-shogaol was evaluated in two different strains, Mycobacterium smegmatis and Candida albicans, using the in vitro checkerboard method. With M. smegmatis, isoeugenol (at ½ MIC) was able to lower the MIC (minimum inhibitory concentration) of isoniazid and 6-paradol by 800 percent (10→1.25 μg/mL) and 400 percent (30→7.5 μg/mL), respectively. Against C. albicans, Isoeugenol (at ½ MIC) was also able to lower the MIC of 6-paradol by 1600 percent (60→3.75 μg/mL). Similar synergistic effects were not observed between isoeugenol and 6-shogaol. Eugenol failed to exhibit any of the synergistic effects of isoeugenol under the same experimental conditions. Isoeugenol is a promising enhancing agent for compounds with weak antimycobacterial and anticandidal activities. 6-Paradol may be a potential candidate for further combination studies due to its broader antimicrobial effect against both M. smegmati...