Comparison of in vitro antibacterial activity of steeping and decoction extracts of four plants against Escherichia coli and Staphylococcus aureus

Abstract

Plants have secondary metabolites that can protect them against herbivores and microbes. Aqueous and ethanolic extracts of these metabolites can be an effective replacement to antibiotics due to the increasing antibiotic-resistance of some bacteria. The effectivity of aqueous decoction and steeping extracts of four plants, Cymbopogon cilralus, Coleus blumei, Plectranthus amboinicus and Curcuma tonga were tested on E. colt and S. aureus. Disc diffusion test and broth dilution test were used to measure antibacterial activity of the extracts with ciprofloxacin as standard. After a two-way ANOVA and Games-Howell multiple comparison test, it was determined that steeping and decoction extracts from all plants used did not have antimicrobial activity against E. coli and S. aureus. Both bacteria were only found to be susceptible to the positive control ciprofloxacin with E. coli being more sensitive. Secondary metabolites are complex molecules not limited to function in antibacterial activity. Most of these are used by plants in antiherbivory, which require activation via interaction with chemical pathways of herbivores. Depending on the plant species, different secondary metabolites function differently as phytoalexic compounds. Secondary metabolites functioning as phytoalexins from the four plants have not been extracted from the concentration of 10% w/v steeping and decoction leaf extracts. By not exposing the leaves to sunlight before crushing, possible phytoalexic compounds that can be extracted using distilled water requiring photoactivation cannot function. This study shows that aqueous extraction method is not an ideal extraction method for some phytoalexic compounds of Cymbopogon citratus, Coleus blumei, Plectranthus amboinicus and Curcuma longa.