The Synergistic Antimicrobial Effect of Vernonia amygdalina (Bitter Leaf) Extract and Ciprofloxacin on Escherichia coli

Abstract

Since many microorganisms are developing resistance to synthetic medications, finding newer sources of antibiotics is a global challenge that occupies research organisations, pharmaceutical firms, and academia. This study aimed to evaluate and determine the synergistic antimicrobial effect of Vernonia amygdalina (bitter leaf) extract and antibiotics on Escherichia coli. Plant leaves were air-dried, crushed, and immersed in ethanol. Wastewater samples were collected from the NDDC Hostel wastewater dump site using sterile, screw-capped sample containers. The samples were aseptically collected to prevent external contamination and were properly labelled before being transported immediately to the Microbiology Laboratory for analysis. The results revealed that total heterotrophic bacterial counts ranged from 1.1 ± 0.13 × 10^7 CFU/ml to 3.2 ± 0.26 × 10^7 CFU/ml, with Sample W2 having the higher count, while total coliform counts ranged from 1.5 ± 0.14 × 10^5 CFU/ml to 2.9 ± 0.26 × 10^5 CFU/ml, with Sample W2 having the highest count; total faecal counts (TFC) ranged from 8.0± 0.10×10^3 CFU/ml to 11.0± 0.23 × 10^3, with Sample W2 having the highest count. The susceptibility results revealed considerable variation in the antibacterial activity of ciprofloxacin, Vernonia amygdalina extract, and their combinations against the bacterial isolates. Ciprofloxacin alone produced little inhibition in some isolates, indicating some degree of resistance or intermediate susceptibility (12–16 mm) against most isolates and 18 mm in some isolates, while the plant extract alone exhibited very weak antibacterial activity (0–30 mm) at varying concentrations. However, the ciprofloxacin–plant extract mixtures produced markedly larger zones of inhibition, reaching 22 mm in isolate E4 and 30 mm in E2. These findings suggest that combining ciprofloxacin with Vernonia amygdalina extract enhanced antibacterial activity against some isolates, indicating a possible synergistic interaction between the antibiotic and the phytochemicals present in the plant extract.