title: In vitro antibacterial and time-kill evaluation of the Erythrina caffra Thunb. extract against bacteria associated with diarrhoea.
abstract: The antibacterial activities of stem bark ethanolic extract of Erythrina caffra Thunb. against bacteria in diarrhoea was determined in vitro by the agar diffusion and dilution, macrobroth dilution, and time-kill assay methods. The result showed that the extract produced inhibition zones ranging between 15 ± 1.0 mm and 23 ± 1.0 mm, and the bacteria were susceptible at concentrations ranging between ≤100 and ≤1000 μg/mL. While the MICs of the extract ranged between 39.1 and 625 μg/mL, and the MBCs ranged between 78.1 and 625 μg/mL, the MICs of Micrococcus luteus, Proteus vulgaris CSIR 0030, Enterococcus faecalis KZN, and Staphylococcus aureus OK₃ were less than 100 μg/mL, and the mechanisms of antibiosis indicated that the crude ethanolic extract was highly bactericidal against the entire test bacteria isolates. In the time-kill assay, the average log reduction of the viable cell count ranged between 0.916 log₁₀ and 1.851 log₁₀ cfu/mL on incubating the bacteria for 4 h at the MICs, while the reduction ranged between 0.183 log₁₀ and 1.105 log₁₀ cfu/mL after 8 h of incubation. Incubating the bacteria for 4 h at 2 × MICs resulted in the reduction of the viable cell count to between -0.264 log₁₀ and 0.961 log₁₀ cfu/mL, while the average log reduction ranged between -3.968 log₁₀ and -0.425 log₁₀ cfu/mL after 8 h of incubation with Micrococcus luteus, Proteus vulgaris CSIR 0030, and Staphylococcus aureus OK₃ being the most highly affected bacteria. The result showed that the extract exhibited broader-spectrum antibacterial activity and justifies the use of Erythrina caffra in the folkloric medicine for treating gastrointestinal infections in South Africa.
authors.affiliation: Phytomedicine Research Centre, Department of Botany, University of Fort Hare, Alice 5700, South Africa.
authors.forename: Olufunmiso Olusola
authors.initials: OO
authors.lastname: Olajuyigbe
authors.forename: Anthony Jide
authors.initials: AJ
authors.lastname: Afolayan
mesh_terms: D000900:Anti-Bacterial Agents / Q000008:administration & dosage; D018407:Bacterial Physiological Phenomena / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004403:Dysentery / Q000188:drug therapy / Q000382:microbiology*; D004895:Erythrina / Q000737:chemistry*; D006801:Humans; D007928:Lethal Dose 50; D010936:Plant Extracts / Q000008:administration & dosage*
chemical_list: D000900:Anti-Bacterial Agents; D010936:Plant Extracts