Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is recognized as a serious clinical problem worldwide. Consequently, a recent investigation was conducted on the antibacterial activity and aerial part of Kalimeris yomena Kitamura. The antibacterial activities of ethanol (EtOH) extract of K. yomena and its n-hexane, EtOAc, n-BuOH and H₂O fractions were evaluated against 15 strains of MRSA and 1 standard methicillin-susceptible S. aureus(MSSA) strain. The n-hexane fraction showed a positive antibacterial activity against all the tested strains. The minimum inhibitory concentrations (MICs) of n-hexane fraction were in the range of 31.3 to 250 μg/ml. The disc diffusion test diameter of the inhibition zone was in the range of 12 to 17 mm. Thereafter, the combination of n-hexane fraction of K. yomena (HFK) + ampicillin (AM) or oxacillin (OX), fractional inhibitory concentrations index (FICI) values for HFK + AM ranged between 0.25 and 0.5, and HFK + Ox ranged between 0.5 and 0.56, which show increased synergistic effects. Determining time-kill curves also confirmed the improved synergism of HFK and AM combination against 4, 8, 12 and 24 h cultured MRSA. This result encouraged us to think that n-hexane fraction of aerial part of K. yomena can be used as a natural antibacterial agent.

Key words: Kalimeris yomena Kitamura, aster yomena, antibacterial, ethanol (EtOH) extract, combination methicillin-resistant Staphylococcus aureus (MRSA).