Bacterial exopolysaccharide (EPS)-coated ZnO nanoparticles showed high antibiofilm activity and larvicidal toxicity against malaria and Zika virus vectors.

In this study, a novel and effective approach was performed to synthesize ZnO nanoparticles (ZnO NPs) using the exopolysaccharides (EPS) from the probiotic strain Bacillus licheniformis Dahb1. EPS acted as reducing and stabilizing agent for the formation of EPS-ZnO NPs by co-precipitation method. Structural characterization was investigated by a surface plasma resonance centered at 375nm in UV-vis spectrum. FTIR spectrum exhibited functional groups with strong absorption peak at 3814.7-420cm-1. XRD showed the crystalline nature of EPS-ZnO NPs. TEM showed that the EPS-ZnO NPs were hexagonal in shape, with size within the range of 10-100nm. The presence of Zn was confirmed by EDX analysis. Antibacterial activity of EPS-ZnO NPs was demonstrated as 100μg/ml significantly inhibited the effective growth control of Gram-negative (Pseudomonas aeruginosa and Proteus vulgaris) and Gram-positive (Bacillus subtilis and Bacillus pumilus) bacteria. Light microscopy and confocal laser scanning microscopy evidenced that the antibiofilm activity of EPS-ZnO NPs was higher against Gram-negative bacteria over Gram positive bacteria. EPS-ZnO NPs also inhibited the biofilm growth of Candida albicans at the concentration of 75μg/ml. The hemolytic test showed low cytotoxicity of EPS-ZnO NPs at 5mg/ml. In addition, EPS-ZnO NPs achieved 100% mortality against third instars mosquito larvae of Anopheles stephensi and Aedes aegypti at very low doses. Moreover, histology studies revealed the presence of damaged cells and tissues in the mid-gut of treated mosquito larvae. The multipurpose properties of EPS-ZnO NPs revealed in the present study can be further considered for pharmaceutical, parasitological and entomological applications.