Jesela Angeli R. Agas1, Rafael Miguel C. Alibarbar1, Darylle Marie Hannah M. Ang1, Sebastian Angelo B. Balmes1, Antoinette Dominique M. Bautista1, Erin Dominique M. Buenaventura1, Mark Kevin P. Devanadera2, Vivian Villegas1, Maria Luisa R. Olano1
Background: The emergence of antibiotic-resistant microorganisms, particularly Escherichia coli, underscores the need for alternative infection control strategies. This study investigated the antibacterial activity of oregano (Plectranthus amboinicus) and lemongrass (Cymbopogon citratus), both rich in phenols and flavonoids with antimicrobial properties.
Methods: Macrobroth dilution susceptibility testing was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the samples. To evaluate the interaction between the antimicrobial agents, the fractional inhibitory concentration (FIC) index was calculated. This approach allowed the assessment of whether the combined agents exhibited synergistic, additive, or antagonistic effects. The study specifically hypothesized that combining the agents would enhance antimicrobial activity through synergistic interactions, resulting in improved inhibition and bacterial killing compared to the effects of each agent used alone.
Results: However, statistical analyses showed that the MIC data were not normally distributed (P<0.001) and that the assumption of homogeneity of variances was violated (P<0.001). Treatment type significantly influenced MIC (P=0.001), whereas concentration (P>0.05) and the treatment–concentration interaction (P>0.05) did not show significant effects. Post hoc comparisons revealed significant differences between bleach and lemongrass extract (P=0.009) as well as between bleach and oregano extract (P=0.02), while no significant difference was observed between lemongrass and oregano extracts (P=0.60). Overall, the results indicated additive rather than synergistic effects, with bleach demonstrating bactericidal activity.
Conclusions: Although the combination was effective in inhibiting bacterial growth, it cannot fully replace bleach for complete microbial eradication. However, the results indicate its potential as a natural disinfectant, particularly for use in less critical or low-risk settings where harsh chemical disinfectants are not required.
