Antimicrobial activity of leptospermone and its derivatives against human intestinal bacteria

The anaerobic growth inhibiting activity of the essential oil of Leptospermum scoparium seeds against intestinal bacteria was evaluated in vitro. The essential oil at 5.0 mg/disc strongly (+++) inhibited the growth of Clostridium difficile and Clostridium perfringens, but did not inhibit the growth of Bifidobacterium breve, Bifidobacterium longum, Escherichia coli, or Lactobacillus casei. Spectroscopic analyses revealed that the active component of the essential oil was leptospermone. Leptospermone strongly inhibited the growth of C. difficile and C. perfringens at 1.0 mg/disc and moderately inhibited their growth at 0.5 mg/disc. However, leptospermone did not inhibit the growth of B. breve, B. longum, and L. casei. When compared with the leptospermone derivatives, 1,2,3-cyclohexanetrione-1,3-dioxime exerted strong inhibition against C. perfringens and moderate inhibition against C. difficile at 0.5 mg/disc, whereas the other derivatives exerted weak or no growth inhibition against all bacteria tested. Taken together, these results indicate that cyclohexanetrione is required for triketone derivatives to inhibit the growth of C. difficile and C. perfringens. These findings indicate that L. scoparium seed-derived materials and 1,2,3-cyclohexanetrione-1,3-dioxime are naturally occurring antimicrobial agents that could be useful in the development of new agents for the specific control of C. difficile and C. perfringens.