Evaluating the Antimicrobial Activity of Crude Extracts from Leaves, Flowers and Roots of Iris versicolor and Nerium oleander Plants Against Escherichia coli and Staphylococcus aureus

Abstract

Bacterial infections are prevalent in most parts of Kenya and cause diseases like pneumonia, typhoid, cholera, and meningitis. This has contributed to unsustainable socio-economic development following the emergence of antimicrobial-resistant strains of bacteria and, hence, the need for alternative strategies that are effective against bacteria and environmentally safe. This study evaluated the antimicrobial activity of crude extracts from leaves, flowers and roots of Iris versicolor and Nerium oleander plants against Escherichia coli and Staphylococcus aureus. The plant parts were macerated and extracted to obtain phytochemicals that were then identified under different classes of compounds by treating them with varying reagents following standard laboratory procedures. To assess antimicrobial activity, discs were infused with an antimicrobial compound derived from the leaf, flower, and root extracts of N. oleander and I. versicolor at a concentration of 1000 µg/ml. Bacterial isolates (inoculum) were then introduced into plates containing Mueller-Hinton agar media. Infused discs were dispensed aseptically on the plates. The discs were pressed to ensure contact between the agar and the disc and incubated at 37 °C for 24 hrs. The Kirby-Bauer method was used to assess the antibacterial efficacy of the plant extracts against the bacterial strains Staphylococcus aureus and Escherichia coli. The crude plant extracts showed a greater zone of inhibition ranging from 2.5 mm to 3.2 mm in diameter, irrespective of the plant part and the test micro-organism. The methanolic crude extract of N. oleander leaves showed a greater zone of inhibition against Staphylococcus aureus at 3.1 mm and 2.9 mm against E. coli. The zone inhibited by the crude extract on S. aureus showed no growth of the micro-organisms; this was observed on all the crude extracts, irrespective of the extracting solvent, on both E. coli and S. aureus. The methanolic crude extract of N. oleander flowers showed a greater zone of inhibition against S. aureus at 2.9 mm. The hexane crude extract of I. versicolor leaves showed the least zone of inhibition against E. coli at 2.2 mm in diameter. This showed that the plant crude extracts exhibited much higher activity against S. aureus, followed by E. coli