Exopolysaccharide-mediated silver nanoparticles produced by Lactobacillus brevis NM101-1 as antibiotic adjuvant

A green, simple and effective approach was performed to synthesize potent silver nanoparticles using bacterial exopolysaccharide as both a reducing and stabilizing agent. The formation of nanoparticles was first screened by measuring the surface plasmon resonance peak around 400 nm using UV-vis spectroscopy. The morphology of the synthesized AgNPs was determined using TEM, which indicated that the AgNPs were spherical in shape and with an average size of 11-25 nm. The presence of elemental silver of the AgNPs was confirmed by EDX analysis. The possible functional groups of EPS responsible for the reduction and stabilization of AgNPs were evaluated using FTIR. The EPS reduced AgNPs showed excellent antibacterial, and antibiofilm activities against various human pathogenic bacteria. In addition, the efficiency of AgNPs with various broad-spectrum antibiotics against the tested strains was evaluated. It is evident that, the antibacterial and antibiofilm activities of the selected antibiotics were increased in the presence of AgNPs. The increase in activity was more pronounced for gram-negative bacteria Pseudomonas aeruginosa and E. coli. Interestingly, the combination of antibiotics with AgNPs has significantly increased the membrane protein leakage and ROS generation than antibiotics or AgNPs alone. This work supports that AgNPs can be used to enhance the activity of existing antibiotics against gram-negative and gram-positive bacteria for the treatment of infectious diseases.