Study on antibacterial properties of heated oyster shell particle against Bacillus subtilis spores in rainwater by response surface methodology based on central composite design

Taiwan's oyster industry produces shell waste in abundant quantities every year. This study explored the feasibility of applying this resource as a simple and low-cost disinfectant to improve the microbial quality of harvested rainwater. Critical parameters affecting the disinfection efficacy of calcined oyster shell particles, i.e., heating temperature and duration, dosage, and contact time of the calcined shell material against Bacillus subtilis endospores in rainwater, were investigated. A central composite design of response surface methodology was employed to study the relative effects. As estimated from R² coefficients, a quadratic model was identified to predict the response variable satisfactorily. Results indicated that the heating temperature, dosage, and contact time of the calcined material in the rainwater significantly influenced (p < 0.05) the sporicidal effect, consistent with the prior literature on calcined shells of similar nature. However, heating time had a relatively low influence on the sporicidal impact, suggesting that the rate of shell activation, i.e., conversion of the carbonate compound in the shell material to oxide, occurs rapidly at high calcination temperatures. In addition, the sterilization kinetics for heated oyster shell particles in aqueous media under stagnant storage conditions were investigated and found to be in good agreement with Hom's model.

Growth, secondary metabolite production, and in vitro antiplasmodial activity of Sonchus arvensis L. callus under dolomite [CaMg(CO3)2] treatment

Malaria is still a global health problem. Plasmodium is a single-cell protozoan parasite that causes malaria and is transmitted to humans through the female Anopheles mosquito. The previous study showed that Sonchus arvensis L. callus has antiplasmodial activity. Several treatments are needed for callus quality improvement for antimalarial compound production. This study aimed to examine the effect of dolomite [CaMg(CO3)2] on growth (morpho-anatomical structure and biomass), secondary metabolite production, and in vitro antiplasmodial activity of S. arvensis L. callus. In this study, leaf explants were grown in Murashige and Skoog medium with a combination of 2,4-dichlorophenoxyacetic acid (2,4-D, one mg/L) and 6-benzyl amino purine (BAP, 0.5 mg/L) with dolomite (50, 75, 100, 150, and 200 mg/L). The 21 days callus ethanolic and methanolic extract were analyzed by gas chromatography-mass spectrometry (GC-MS) and thin-layer chromatography (TLC). The antiplasmodial test was performed on a blood culture infected with Plasmodium falciparum strain 3D7 using the Rieckmann method. The results showed that dolomite significantly affected callus growth, metabolite profile, and in vitro antiplasmodial activity. Dolomite (150 mg/L) showed the highest biomass (0.590 ± 0.136 g fresh weight and 0.074 ± 0.008 g dry weight). GC-MS analysis detected four compounds from callus ethanolic extract. Pelargonic acid, decanoic acid, and hexadecanoic acid were major compounds. One new terpenoid compound is based on TLC analysis. S. arvensis L. callus has antiplasmodial activity with the IC50 value of 5.037 μg/mL. It was three times lower than leaf methanolic extract and five times lower than leaf ethanolic extract.

Antimicrobial Characteristics of Heated Eggshell Powder

Eggshells have high bioavailability and can be used as a source of calcium. The main component is CaCO3, which, when heated, is converted to CaO. Seashells are also mainly composed of CaCO3 and were previously found to exhibit antimicrobial activity after being heated. In this study, heated eggshell powder (HESP) was found to have antimicrobial activity against bacterial vegetative cells, fungi and bacterial spores. Parameters, such as the minimum inhibitory concentration, were determined with kinetic analysis using an indirect conductimetric assay. Moreover, HESP was able to kill the Bacillus subtilis spores. There were no significant differences in the activity between HESP, heated scallop-shell powder and pure CaO. The MIC values for HESP against bacteria and fungi were 0.29-0.43 and 1.3-1.5 mg/mL, respectively. Against B. subtilis spores, a reduction of two orders of magnitude of viability was confirmed following 20 min of treatment at 10 mg/mL at 60 ℃. The active oxygen generated from the HESP slurry was examined with chemiluminescence. The intensity of this increased with increasing concentrations of the HESP slurry. This suggests that HESP could be used as a natural antimicrobial agent. Although a high pH is the main contributor to this antimicrobial activity, active oxygen species generated from HESP are likely to be the main antimicrobial agents..