BACTERIAL EXOPOLYSACCHARIDE-MEDIATED SYNTHESIS OF SILVER NANOPARTICLES AND THEIR APPLICATION ON BACTERIAL BIOFILMS

Abstract

The development of multi-drug-resistant bacteria and their biofilm formation capabilities has decreased the effectiveness of antibiotics and other antimicrobial agents. Silver nanoparticle (AgNP) is currently being explored as an alternative strategy in countering biofilm-related infections. In this study, AgNP was biosynthesized using the extracted exopolysaccharide (EPS) from two obligate alkaliphilic bacteria, Bacillus krulwichiae M2.5 and Bacillus cellulosilyticus M4.1, isolated from a hyperalkaline spring in Zambales, Philippines. The samples exhibited an absorption peak at around 420 nm corresponding to the surface plasmon resonance of AgNPs as shown by UV-Vis analysis. The Fourier transform infrared (FTIR) spectroscopy spectra revealed functional groups in the EPS such as hydroxyl and carboxyl involved in the reduction of Ag+ to AgNP. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) spectroscopy showed stable irregular and spherical AgNPs with an average size of 25.88 ± 10.49 nm and 23.99± 8.43 nm for B. krulwichiae M2.5 EPS-AgNP and B. cellulosilyticus M4.1 EPS-AgNP, respectively. The biosynthesized AgNPs significantly inhibited the biofilm formation of Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus in a dose-dependent manner as determined by microtiter plate assay. However, the results showed a reduced inhibitory effect of the synthesized AgNPs on established biofilms indicating the need for higher AgNP concentration. This study demonstrates that EPS from bacteria adapted to alkaline conditions can be used for efficient AgNP biosynthesis with potential biomedical applications.