Antimicrobial activity of the ethanolic root extract of mezoneuron benthamianum baill (Caesalpiniaceae)
This study investigated the activities of the ethanolic root extract of Mezoneuron benthamianum Baill (Caesalpiniaceae) and its partitioned fractions on some microbial isolates from the oral cavity and determined the killing rate of the most active fraction. This was with a view to providing scientific basis for the use of the root in the treatment of oral infections. The root of M. benthamianum was air-dried, ground to powder and macerated using 70 % ethanol with constant shaking with a mechanical shaker for 72 hours. The extract was concentrated in-vacuo at 50 oC using a rotary evaporator and freeze dried. The in-vitro susceptibility test was done with the ethanolic root extract and its partitioned fractions (petroleum spirit, chloroform, ethyl acetate and aqueous) on Staphylococcus aureus (NCIB 8588) and clinical isolates of Streptococcus mutans, Streptococcus pyogenes, Streptococcus salivarius, Staphylococcus aureus and Candida albicans isolated from human oral cavity using the agar well diffusion method. The minimum inhibitory concentration of the fractions was determined using the two fold agar dilution method at a range of 0.39 to 25 mg/ml for each fraction. The time-kill-assay for the most active fraction i.e. the ethyl acetate fraction was carried out on all the organisms. Bio-autographic assay was also carried out to find out the component that is responsible for its antimicrobial activities. The values obtained were subjected to inferential statistical analysis. The result showed that the ethanolic root extract had appreciable activity against all the test organisms at varying concentrations of 25 mg/ml, 50 mg/ml and 100 mg/ml with increasing zones of inhibition as the concentration increased. The rank order for the activity of the partitioned fractions at the test concentration of 25 mg/ml was observed as ethyl acetate (20.6 mm-23.7 mm) > chloroform (14.7 mm-18.7 mm) > aqueous (13.7 mm-18.3 mm) and > petroleum spirit (11.3 mm-13.3 mm). The minimum inhibitory concentration gave a rank order of ethyl acetate (0.039 mg/ml) < chloroform (0.78 mg/ml-6.25 mg/ml) < aqueous (3.13 mg/ml-12.5 mg/ml) < petroleum spirit (6.25 mg/ml- 25 mg/ml). It was also observed that the activity of the ethyl acetate fraction was higher than the activity of the ethanolic extract at the same concentration of 25 mg/ml. The killing rate experiment showed that the ethyl acetate fraction had a rapid rate of action on the organisms at the test concentrations of 0.39 mg/ml (MIC concentration) and 0.78 mg/ml (MICx2). At concentration of 1.17 mg/ml (MICx3) the time of kill of all the organisms by the ethyl acetate fraction was ≤ 5 minutes, which was similar to the standard antibiotics used at their MIC values e.g. 0.039 mg/ml of Ampicillin and Tetracycline for the bacteria; and 0.078 mg/ml of Amphotericin B for the fungus used. The chromatographic result of the ethyl acetate fraction showed two distinct bands and the bio-autographic assay performed on the plate revealed that only one component (the upper band) proved effective in inhibiting all the test organisms. The study concluded that M. benthamianum ethanolic root extract was highly effective against oral isolates with its ethyl acetate fraction being the most active.