Anti-Pythium insidiosum activity of bioactive compounds from medicinal plants

Pythiosis is a serious disease caused by the aquatic oomycete Pythium insidiosum that mainly affects mammals. Unlike fungal and bacterial resistance induced by the indiscriminate use of drugs, P. insidiosum has low susceptibility to antifungal drugs. In this sense, essential oils and their major components emerge as a promising treatment line for this disease. Given the above, this study sought to verify P. insidiosum (n = 34) susceptibility to the bioactive compounds eugenol, alpha-terpineol, menthol, and carvacrol and correlate them with the respective essential oils of Eugenia caryophyllata, Melaleuca alternifolia, Mentha piperita, and Origanum vulgare. The essential oils and bioactive compounds were purchased commercially and tested according to the Clinical and Laboratory Standards Institute protocol M38-A2. Our findings showed that eugenol, alpha-terpineol, and carvacrol had superior anti-P. insidiosum action than their respective essential oils, suggesting that they may be responsible for inhibitory activity against P. insidiosum. Notably, the major compound with the best anti-P. insidiosum activity was alpha-terpineol; nonetheless, menthol showed less activity than its essential oil. The results imply that essential oils and their major compounds may be important allies in treating pythiosis, expanding the perspectives of developing new drugs with anti-P. insidiosum activity.