Antibacterial activity of Lactobacillus plantarum BS25, Pediococcus acidilactici S3 crude, and partially-purified cell-free supernatants against methicillinsusceptible and methicillin-resistant Staphylococcus aureus strains

Abstract

Background: The rising public health threat brought about by antibiotic resistance, such as of Staphylococcus aureus, opened doors of opportunities for natural products research to explore novel antimicrobial agents.

Objective: This study aimed to determine the antimicrobial activity of cell-free supernatants from
Lactobacillus plantarum BS25 and Pediococcus acidilactici S3 against Staphylococcus aureus (ATCC# 25923) and methicillin-resistant S. aureus (ATCC# 33591).

Methodology: Cell-free supernatants (CFS) of Lactobacillus plantarum BS25 and Pediococcus acidilactici S3, isolated from fermented rice-fish mixture balao-balao and fermented spicy sausage longganisa, respectively, were tested against methicillin-susceptible (MSSA, ATCC 25923) and methicillin-resistant (MRSA, ATCC 33591) Staphylococcus aureus strains for antibacterial activity using the resazurin assay.

Results: Both BS25 and S3 CFS showed high activities against MSSA and partial inhibition against MRSA. Proteinaceous components of the CFS were extracted using ammonium sulfate precipitation with BS25 and S3 exhibited low activities against MSSA but partial inhibition was observed against MRSA. Other small molecules were extracted from the CFS through liquid-liquid extraction using ethyl acetate and tested in 100, 250, 500, 750, and 1000 ppm concentrations. The 1000-ppm concentrations of the BS25 and S3 ethyl acetate extracts achieved the highest antibacterial activity against MSSA and MRSA.

Conclusion: This study showed that the crude cell-free supernatants, ammonium sulfate precipitates, and ethyl acetate extracts of BS25 and S3 CFS exhibited potential in inhibiting Gram-positive MSSA and MRSA. However, the partially-purified samples require relatively high concentrations in order to produce significant inhibition activities and therefore require further purification.