Date of Completion

2025

Document Type

Thesis

Degree Name

Bachelor of Science in Biochemistry

Keywords

Antibacterial, Lacticaseibacillus

Abstract

Dental caries is a prevalent microbe-mediated oral disease characterized by the localized demineralization of dental tissues. The acid-producing and acid-tolerating microbe, Streptococcus mutans, is identified as the main etiologic agent in the progression of caries. Although ubiquitously found in the normal oral microbiome, the emergence of antimicrobial-resistant S. mutans strains has prompted the urgent search for alternative antibacterial compounds to treat caries. Recently, bioactive compounds from the cell-free supernatant (CFS) of probiotic bacteria have gained widespread attention and have been shown to possess potent growthinhibitory and bactericidal properties against pathogens. Herein, we partially characterized the aqueoussoluble extracts from Lacticaseibacillus casei CFS and investigated their antibacterial properties against S. mutans BIOTECH 10231. A simple buffer-assisted biological method to extract the aqueous-soluble extracts of CFS from agar-plated L. casei was performed. Spectrophotometric Bradford assay-based quantification revealed 0.124 ± 0.323 mg/mL of protein from the aqueous-soluble extracts of L. casei CFS. Biuret tests qualitatively confirmed the presence of proteins. However, protein profiling through SDS-PAGE failed to reveal significant protein bands, primarily indicating a low protein concentration in the extract. Normal phase paper chromatography experiments, on the other hand, identified the presence of selected amino acids such as cysteine (Rf = 0.25), aspartic acid and histidine (Rf = 0.18), arginine, asparagine, and glycine (Rf = 0.5), serine and valine (Rf = 0.33), and methionine, phenylalanine, proline, tryptophan, and tyrosine (Rf = 0.62). By fitting the data via the Gompertz model, activity assays using the crude protein-containing aqueous-soluble extracts from L. casei CFS revealed moderate antimicrobial properties (MIC = 20.2074 ± 0.6119 μg/mL; NIC = 16.1929 ± 1.4147 μg/mL; MBC > 50.0 μg/mL) compared to the positive control chlorhexidine gluconate (MIC = 1.1494 ± 0.6456 μg/mL; NIC = 1.0510 ± 0.6460 μg/mL; MBC = 4.00 μg/mL). Overall, the study suggests L. casei CFS as a good source of bioactive antibacterial compounds against S. mutans. Further advancements in probiotic research may highlight their potential as novel therapeutic strategies for the prevention and treatment of other oral pathologies (e.g., periodontal diseases).

First Advisor

Walter Aljohn T. Espiritu, RCh

Second Advisor

Nedrick T. Distor, RCh, MSc

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