Soil modulation effects on the antimicrobial potential and toxicity of Solanum nigrum extracts

Abstract

The use of plants to control pathogenic microorganisms has increased users’ interest in commercial production and the best soil types for antimicrobial efficacies. This study was aimed at evaluating the antimicrobial efficacy of extracts of S. nigrum cultivated on different soil types. Experimental soils were formulated into sandy loam (control), sandy clay loam, silty clay loam, clay loam, and loam. Seedlings of S. nigrum were transplanted into each of the soils. At the onset of flowering, the plants were harvested and extracted with water and acetone. The antibacterial activity of the plant extracts was tested against human pathogenic bacteria. The minimum inhibitory concentration (MIC) of the extracts was also determined. The lethality of brine shrimp nauplii was used to assess the toxicity of the plant extracts. The results demonstrated the efficacy of the extracts from silty clay loam soil MICs of 0.313 on Listeria species but with 1.25 mg/mL on Shigella flexneri, and Escherichia coli respectively. The 50% lethal concentration values of all the S. nigrum extracts were significantly higher than 1000 mg/mL (non-toxic value), demonstrating that none of the extracts is toxic. In the aqueous and acetone extracts, the lowest mortality rates of 3.85 and 5.90% were observed in silty clay loam and sandy loam soils, respectively. The findings of this study reveal that plant extracts from silty clay loam soil have superior antibacterial potential, indicating that soil type influences S. nigrum antimicrobial activities. Silty clay loam soil is recommended for the cultivation of S. nigrum required for antibacterial purposes.