Spent Coffee Grounds Extract Limits Bacterial Proliferation on Human Foot Skin Under Humid Conditions

Natural plant-derived extracts are increasingly recognized for their antimicrobial, antioxidant, and anti-inflammatory properties, making them promising candidates for the prevention and/or treatment of various diseases. Camellia sinensis Azorean Black Tea (ABT) and spent coffee grounds (SCG) were selected due to their high content of bioactive compounds, including catechins, theaflavins, chlorogenic acids, and caffeine, which have demonstrated potential against microbial infections. ABT and SCG extracts were applied to the hallux (big toe) skin of healthy volunteers for 8 h. Samples were collected before and after exposure and cultured on blood agar to determine colony-forming units (CFU), which were normalized to CFU/cm2 of skin. No macroscopic skin alterations, thermographic changes, or early signs of inflammation were observed following exposure to these extracts. While the humid control and ABT exposure groups exhibited increased bacterial proliferation, SCG exposure resulted in bacterial levels statistically comparable to those of the dry control, with significantly lower bacterial growth than the humid control and ABT exposure groups. Overall, these findings add to the growing evidence supporting the use of natural extracts as sustainable options for skin protection and the regulation of microbial proliferation.