Green synthesis of walnut shell hydrochar, its antimicrobial activity and mechanism on some pathogens as a natural sanitizer

Hydrochar of waste walnut shells (WSH) was synthesized in the eco-friendly subcritical water medium (SWM) and its potential to fight against Klebsiella pneumoniae (K. pneumoniae), Staphylococcus aureus (S. aureus), Candida albicans (C. albicans) and Candida parapsilosis (C. parapsilosis) was investigated. Minimum Inhibitory Concentration (MIC) values of the WSH were 3.01 g/mL, 2.06 g/mL, 1.95 g/mL, and 3.12 g/mL for K. pneumoniae, S. aureus, C. albicans and C. parapsilosis, respectively. Survival of the pathogens was investigated by 3 min surface disinfection test exposure to WSH. While the highest inhibition was seen for C. parapsilosis (96.67%) on paper surface with 0.3 g/mL of bovine serum albumin (BSA), the lowest inhibition was determined for C. albicans (6.44%) on the plastic glass surface with 3 g/mL of BSA. An increase in protein, DNA, and potassium ion (K+) leakage was observed after microorganisms were incubated with WSH. This study provided an experimental basis for the practical application of WSH as a natural sanitizer agent.

Automated summary

The hydrochar of waste walnut shells (WSH) showed potential in inhibiting the growth of Klebsiella pneumoniae, Staphylococcus aureus, Candida albicans, and Candida parapsilosis. The study found that the inhibition was the highest for C. parapsilosis and the lowest for C. albicans. After exposure to WSH, there was an increase in leakage of proteins, DNA, and potassium ions from the microorganisms.