title: Evaluation of the anti-Listeria potentials of some plant-derived triterpenes.
abstract: BACKGROUND
  Listeriosis is a fatal disease caused by pathogenic Listeria bacteria and it is most prevalent in immune-compromised individuals. The increase in numbers of immune-compromised individuals against a background of Listeria antibiotic resistance, limits listeriosis treatment options. This therefore calls for research into substitute treatments, of which, medicinal plants derived compounds offer a viable alternative.
  
  
  METHODS
  The broth microdilution assay was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of three plant triterpenes namely 3β-hydroxylanosta-9,24-dien-21-oic acid, methyl-3β-hydroxylanosta-9,24-dien-21-oate and 3β-acetylursolic acid, against Listeria monocytogenes, Listeria ivanovii and Listeria grayi species. The chequerboard method was used to assess the interactions between the triterpenes and conventional antibiotics: ampicillin, neomycin, gentamicin and penicillin G. The lactate dehydrogenase membrane damage method was used to assess the triterpenes' membrane damaging potentials against the Listeria bacteria.
  
  
  RESULTS
  The triterpenes' MIC values were found to range from 0.185 to 1.67 mg/ml while, the MBC determination assay results revealed that the test triterpenes were bacteriostatic against the Listeria bacteria. The interactions involving 3β-hydroxylanosta-9,24-dien-21-oic acid were mainly additive with ampicillin and synergistic with neomycin, gentamicin and penicillin G. The interactions involving methyl-3β-hydroxylanosta-9,24-dien-21-oate were mainly antagonistic with ampicillin, indifferent with neomycin, ranging from synergistic to indifference with gentamicin and synergistic with penicillin G. The interactions involving 3β-acetylursolic acid were mainly indifferent with ampicillin, synergistic with neomycin and gentamicin while ranging between synergistic and additive with penicillin G. The low levels of cytosolic lactate dehydrogenase released from the cells treated with 4× MIC concentration of the triterpenes in comparison to that of cells treated with 3% Triton X-100 proved that membrane damage was not the mode of action of the triterpenes.
  
  
  CONCLUSIONS
  This study therefore shows the potential that these plant triterpenes have in listeriosis chemotherapy especially as shown by the favourable interactions they had with penicillin G, one of the antibiotics of choice in listeriosis treatment.
authors: Department of Biochemistry and Microbiology, University of Zululand, P Bag X1001, KwaDlangezwa, 3886, South Africa. propafadzo@gmail.com.
authors: Dambudzo
authors: D
authors: Penduka
authors: Rebamang
authors: R
authors: Mosa
authors: Mthokozisi
authors: M
authors: Simelane
authors: Albert
authors: A
authors: Basson
authors: Anthony
authors: A
authors: Okoh
authors: Andy
authors: A
authors: Opoku
mesh_terms: D000900:Anti-Bacterial Agents / Q000302:isolation & purification / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects; D004347:Drug Interactions; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008087:Listeria / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D010936:Plant Extracts / Q000302:isolation & purification / Q000494:pharmacology*; D010946:Plants, Medicinal / Q000737:chemistry*; D014315:Triterpenes / Q000302:isolation & purification / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D010936:Plant Extracts; D014315:Triterpenes; D007770:L-Lactate Dehydrogenase