Screening of the Antimicrobial Activity of Leaf Extracts from Different Plant Families (Boraginaceae, Fabaceae, Lamiaceae, and Lauraceae) against Microorganisms of Clinical Importance

Traditional medicinal plants serve as potential sources of new antimicrobial agents, since they
possess natural products, including secondary metabolites and their derivatives.
Aims: This study was conducted to investigate the antimicrobial activities of Sassafras albidum
(Nutt.), Ehretia anacua (Terán & Berl.), Melissa officinalis (Linn.), Eysenhardtia texana (Scheele), and
Melissa odorata. Specifically, this study aims to evaluate the antimicrobial potential and to qualitatively
determine presence of secondary metabolites in the different leaf extracts.
Place and Duration of Study: Plant leaves were collected from the San Antonio Botanical Garden in
Texas. The microbial assays and chemical analysis were done at the Department of Biology and
Chemistry, Texas A&M International University, Laredo Texas. This study was done from October
2013 to May 2016.
Methodology: Leaves were collected and aqueous, acetone, diethyl ether and ethanol leaf extracts
were prepared. Antimicrobial activity against bacteria and fungi were investigated via disc diffusion
assay. Phytochemical screening were done to qualitatively determine secondary metabolites.
Results and Conclusion: The ethanol and diethyl E. anacua (Boraginaceae) extracts showed a
statistically significant antimicrobial activity against S. aureus. Although the values, 7.4 mm and 7.5
mm for the ethanol and diethyl ether extracts could be low values for zone of inhibitions, the potential
for E. anacua for anti-S. aureus activity cannot be undermined. Phytochemical analysis showed
detectable presence of alkaloids, diterpenes and phenols in the ethanol and diethyl E. anacua
extracts. Results of this study although preliminary demonstrated the potential of E. anacua as a new
source of bioactive metabolites. Phytochemical analysis demonstrated that ethanol E. anacua extract
was positive for alkaloids, cardiac glycosides, diterpenes, and phenols, while diethyl ether E. anacua
extract was positive for alkaloids, diterpenes, and phenols. This is the first report on E. anacua’s
antimicrobial activity and their secondary metabolites. Alkaloids, diterpenes, and phenols either
individually or synergistically are likely responsible for the observed antimicrobial activity. Further
investigations are needed in order to specifically identify, quantify and isolate the bioactive
compounds that might act against S. aureus associated skin infections.