Methanolic extract of the plant Alternanthera repens was obtained using the cold method of extraction. The bioactivity of the extracts was tested against bacterial isolates namely: Staphylococcus aureus, Streptococcus faecalis, Escherichia coli, Bacillus subtilis, Bacillus cereus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi, and Proteus mirabilis. The agar well diffusion method was used for the in-vitro antibacterial bioassay and it revealed that the extract was able to inhibit the growth of the test organisms at a concentration of 25.0 mg/ml except Escherichia coli, Streptococcus faecalis, and Salmonella typhi which were resistant. The extract had the highest zone of inhibition (30mm) on Staphylococcus aureus, followed by Klebsiella pneumonia and Bacillus subtilis with 26.0 mm and 25.0 mm respectively. The minimum inhibitory concentration (MIC) of the plant extract ranged from 25.0 to 3.125 mg/ml. The antibacterial activity of the methanolic plant extract compared favourably well with commercial antibiotics. The rate of killing of the plant extract on the isolates showed a decrease in the bacterial count with an increase in the exposure time to the extract. Phytochemical screening tests showed the presence of saponins, alkaloids, salkowski, and keller killianie in the plant extract
Keywords: Antibacterial, Phytochemical screening, Rate of killing, Zone of inhibition
