Calcined marine coral powders as a novel ecofriendly antimicrobial agent

In this study, natural waste of marine corals was calcined to prepare an antimicrobial agent. Energy-dispersive X-ray fluorescence spectroscopy showed that the major element and compound of calcined corals were Ca and CaO, respectively, while X-ray photoelectron spectroscopy revealed the occurrence of more than one oxygen species (O_1s) on the surface of calcined corals, which was ascribed to the presence of MgO. Scanning electron microscopy imaging showed that calcined corals had a rough surface and an irregular shape, and the particle size distribution indicated that the average particle size of the calcined corals was 7.3 μm. The calcined corals exhibited large zones of inhibition against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria as well as a fungus (Penicillium sp.), in the antimicrobial tests using well diffusion method. Notably, as a membrane-active and species-specific agent, pronounced antimicrobial activity for calcined corals was observed against S. aureus. Our newly developed bioactive calcined corals could be the potential antimicrobial agents in medical, biological, and food packaging applications.