Inhibition of group A streptococcal infection by Melaleuca alternifolia (tea tree) oil concentrate in the murine model

Aims: To investigate the effect of a water‐soluble Melaleuca alternifolia concentrate (MAC) on group A streptococcus (GAS; Streptococcus pyogenes)‐induced necrotizing fasciitis. Methods and Results: MAC pretreatment (1% and 2% v/v) was able to protect mice from GAS infection in an air pouch model. GAS‐induced mouse death and skin injury were inhibited dose dependently by MAC. Administration of MAC at 6 h post‐GAS infection partially delayed mouse death. Surveys of the exudates of the air pouch of MAC‐treated mice revealed that the survival of infiltrating cells was prolonged, the bacteria were eliminated, and the production of inflammatory cytokines was inhibited. MAC could directly inhibit the growth of GAS in vitro, and the minimal inhibitory concentration (MIC) of MAC for GAS was determined as 0·05% v/v using the time‐kill assay. Furthermore, a sub‐MIC dose of MAC not only enhanced the bactericidal activity of RAW264.7 macrophage cells against GAS but also increased susceptibility of GAS for blood clearance. Conclusions: These results suggest that MAC may inhibit GAS‐induced skin damage and mouse death by directly inhibiting GAS growth and enhancing the bactericidal activity of macrophages. Significance and Impact of the Study: Our results provide scientific data on the use of MAC for the treatment of GAS‐induced necrotizing fasciitis in the murine model.