In vivo and in vitro antibacterial activity of acanthospermal B, a sesquiterpene lactone isolated from Acanthospermum hispidum

Abstract

Acanthospermal B (AcB), the major sesquiterpene lactone (SL) of Acanthospermum hispidum, an herb widely spread in Argentina, is a selective antibacterial agent against Enterococcus faecalis and Staphylococcus aureus, but inactive on Gram-negative and Lactobacillus. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main microorganisms involved in human chronic infection. A balb\c mouse skin infection model was developed to reproduce the lesions caused by acute and chronic infections produced by MRSA. After determination of the maximum concentration of AcB unable to produce tissular injury after intradermal injection, the anti-MRSA effect of AcB was evaluated on skin, liver and spleen tissues of infected mice. AcB, at doses of 2.5 mg/kg, produced a ten times decrease of MRSA growth in skin infection. In addition, the same dose prevented the dissemination to liver and/or spleen. AcB also displayed a bacteriostatic effect, in vitro, on MRSA cultures at 50 µg/mL that seems to be caused by partial denaturation of total bacterial DNA and/or inhibition of the PCR reaction in not denaturized DNA. Finally, total MRSA cell wall lysis occurred at a concentration of 100 µg/mL of AcB after 2 h of exposure.