Antibacterial and resistance –modifying effects of Mezoneuron benthamianum

The ever increasing resistance of human pathogens to current antimicrobial agents is a serious medical problem, and has resulted in the need for novel antibiotic prototypes. The root bark of Mezoneuron benthamianum Baill.(Caesalpinaceae) is used in Ghanaian traditional medicine for the treatment of wounds and other dermal infections. Bioactivity-guided fractionation of the pet. spirit extract led to the isolation of cassane-type diterpenes active against various bacteria and two strains of Staphylococcus aureus possessing the multidrug efflux pumps NorA and TetK (SA1199B and XU212) [1]. Addition of R2 and R3 in the growth medium at 10µg/mL resulted in a 16-fold and 8-fold (Norfloxacin) and 8-fold and 4-fold (Tetracycline) potentiation of activities in both compounds respectively (Table 1). The other three compounds however were not active against the efflux pumps but showed various degrees of activities against other bacteria.

Table 1: Antibacterial susceptibility of test strains in the absence and presence of 10µg/mL of R2 and R3 and 20µg/mL reserpine, a naturally occurring MDR efflux inhibitor serving as a standard modulator, n=3.

Antibacterial agent	MIC of test strain expressing the indicated efflux protein SA 1199B(NorA) XU 212(TetK)
Norfloxacin +R2 +R3 +Reserpine Tetracycline +R2 +R3 +Reserpine	32 2 4 32 NT	NT 128 16 32 32

Ackowledgement: Rita Akosua Dickson is funded by the Commonwealth Scholarship Commission, UK.

Reference: 1. Gibbons, S. et al. (2004), Phytochem. 65: 3249–3254.