Effectiveness of biosynthesized zinc nanoparticles on microbial activity in vitro

Abstract This study aims to determine the effectiveness of zinc nanoparticles on microbial activity in vitro. Zinc nanoparticles, nutrient agar media, Mannitol Rogosa Sharpe Agar (MRSA), tetracycline, distilled water, and several bacteria ( Escherichia coli , Salmonella typhimurium , Lactobacillus sp.) were used in this research. The research methods included zinc biosynthesis with neem leaf extract, culture preparation, media preparation, antimicrobial efficacy testing, and minimum inhibitory concentration (MIC) assessment. The treatments used were sterile distilled water (negative control P0), 50 ppm tetracycline (positive control P1), 1200 ppm of Zn(NO 3 ) 2 ·6H 2 O (P2), 300 ppm of zinc nanoparticles (P3), 600 ppm of zinc nanoparticles (P4), and 1200 ppm of zinc nanoparticles (P5), with four replicates for each treatment. The data obtained were examined using one-way ANOVA, and any statistically significant differences between treatments were further tested with orthogonal contrasts. The software used for analysis was SPSS version 21. The observed parameters included the zone of inhibition, MIC, and optical density at 600 nm. The inhibition zone tests showed that concentrations of 300-1200 ppm effectively inhibited the Escherichia coli and Salmonella typhimurium (Gram-negative bacteria) without interfering with the growth of Lactobacillus sp (Gram-positive bacteria). The MIC and OD600 values were recorded at concentrations of 150-1200 ppm for gram-negative bacteria, with an optical density value of 0.07. It can be concluded that zinc nanoparticles have an antibacterial effect on Escherichia coli and Salmonella typhimurium , with a minimum inhibitory concentration value of 150 ppm.