Date of Completion

2025

Document Type

Thesis

Degree Name

Bachelor of Science in Pharmacy

Keywords

antibacterial activity, cyanobacterial-algal extract, secondary metabolites, staphylococcus aureus, proteus mirabilis, resazurin assay, minimum inhibitory concentration

Abstract

Antimicrobial resistance (AMR) is a growing global health threat, diminishing the efficacy of current treatments. Freshwater cyanobacteria, known for their diverse bioactive compounds, represent a promising source of novel antimicrobial agents. This study investigated the antibacterial potential of methanolic crude extracts from cyanobacteria collected at St. Anthony Falls, Indang, Cavite. The isolates were cultured in BG-11 medium, purified, and identified via 16S rRNA sequencing. Methanolic extraction was followed by Thin-Layer Chromatography (TLC) to detect secondary metabolites. Antibacterial activity against Staphylococcus aureus and Proteus mirabilis was assessed using the Resazurin Assay and Broth Microdilution Method. TLC analysis using two solvent systems—hexane:ethyl acetate (7:3) and ethyl acetate:hexane (7:3)—showed average Rf values suggesting moderately non-polar compounds. No spots were observed at 254 nm, but pink to red spots appeared at 366 nm, indicating that flavonoids and pigments are likely contributors to the bioactive compounds in the cyanobacterial-algal extract. The extract exhibited bacteriostatic effects at sub-inhibitory concentrations: 434.78, 217.39, 108.70, 54.35, 27.18, and 13.59 µg/mL. Hormesis was observed in the MIC assay, explaining the negative percent inhibition values. Negative fluorescence intensity (pink wells) was attributed to the intrinsic fluorescence of pigments in the extract. Future studies are encouraged to use bioreactors for cultivation, ensure culture purity through re-streaking, apply gradient centrifugation for isolation, and utilize more sensitive assays such as ATP-based detection. Lastly, testing against E. coli and using High-Performance TLC for better compound profiling are recommended.

First Advisor

Francess Shaira D. Laquindanum, RPh

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