In Vitro Evaluation of Antibacterial Properties of Biogenically Synthesized Zinc Oxide Nanoparticles on Pathogenic Paddy Bacteria

Zinc oxide nanoparticles (ZnO-NP) were successfully synthesized from aloe vera extract and zinc sulfate as zinc precursor. Characterizations of the ZnO-NP were performed using UV-Vis spectrophotometer, XRD, FESEM and TEM analysis. The absorption peak from UV-Vis was at 380 nm while the XRD diagram displayed high purity ZnO-NP. FESEM and TEM analysis showed agglomerated particles with a wide size distribution range. Polymerase chain reaction (PCR) analysis of Xanthomonas oryzae pv. oryzae (Xoo) pathotype 0.0 generated a product with the size of 230 bp similar to in silico PCR results, verifying the pathotype on a molecular level. Subsequently, the antimicrobial activities of the ZnO-NP against Xoo pathotype 0.0 were assessed. Xoo (108 cfu/ml) were grown in LB broth supplemented with various concentrations of ZnO-NP. Samples were collected at 24, 48 and 72 hours of incubation, grown on LB agar and observed for bacterial growth. Colony forming unit (cfu/ml) values revealed that the number of viable cells decreased with high concentrations of ZnO-NP whereas minimal inhibition was observed at lower ZnO-NP concentrations. At lower bacteria of 103 cfu/ml and at 24 hours incubation, ZnO-NP gave comparable antibacterial effects to commercial ZnO-NP and commercial non-nano ZnO after exposure for 1 hour. However, the antimicrobial effects decreased after 48 hours. It was also noted that the ZnO-NP provides better suppression of bacterial growth at lower bacterial concentrations.