Abstract— Cassia fistula or Golden shower is an ornamental tree found all over southeast asia and it is known for its use in herbal medicine. This study aims to investigate the potential synergism between Cassia fistula ethanolic extract and commonly used antibiotic drugs being amoxicillin, a β-lactam class of antibiotic which is bactericidal; and erythromycin, a macrolide that exhibits bacteriostatic activity against the pathogenic bacterium Staphylococcus aureus. Experimental research method with ten individual and combinatorial treatments was utilized. Dried leaves of Cassia fistula macerated in 70% ethanol then concentrated using rotary evaporator, working concentrations of amoxicillin and erythromycin, and their combinations were used to inhibit the growth of Staphylococcus aureus. Two-fold serial dilution method and assessment of the turbidity of samples using visual spectrophotometer were used to determine the individual and combined treatments’ minimum inhibitory concentration (MIC). Fractional inhibitory concentration (FIC) index was used to determine the extent of potentiation of the combinatorial treatments with regards to the original MIC of antibiotic drugs. Findings of the study revealed that combination of amoxicillin and extract yielded a 10-fold increase in activity (from 4.69±2.21 μg/ml MIC of drug alone to 0.44±0.21 μg/ml MIC in combination with the extract), much higher than that of Erythromycin and extract combination which yielded a 5-fold increase in activity (from 25.00±0.00 μg/ml MIC amoxicillin of drug alone to 4.69±2.21 μg/ml MIC in combination with extract). Both drug–extract combinations showed synergism as defined by their individual FIC (≤ 0.5).

Index Terms— Amoxicillin, Cassia fistula, erythromycin, antibacterial synergism.

Jansel A. Rañin is with Doctor of Medicine Program, College of Medicine - San Beda University, Mendiola Manila, Philippines. Liwayway H. Acero and Lailanie D. Evangelista are with Department of Natural Sciences, College of Arts and Sciences - San Beda University, Mendiola Manila, Philippines.

Cite: Jansel A. Rañin, Liwayway H. Acero, Lailanie D. Evangelista, " Synergistic Antibacterial Activity of Cassia Fistula Ethanolic Extract with Antibiotics Amoxicillin and Erythromycin against Staphylococcus Aureus," International Journal of Bioscience, Biochemistry and Bioinformatics vol. 10, no. 4, pp. 170-179, 2020.

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