Evaluation of the anti-Listeria potentials of some plant-derived triterpenes

Abstract

BackgroundListeriosis 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.MethodsThe 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.ResultsThe 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.ConclusionThis 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.

The antibacterial activities of some plant-derived triterpenes

“…The combined results of the present and previous (Penduka et al, 2014;Mosa et al, 2014b) studies support the postulations that the mode of action of triterpenoids is not yet fully understood (Chung et al, 2011). This then leads to the possible conclusion that the triterpenes work on multiple target sites, such that their mechanism of action is possibly a combination of the blockage of cell division through DNA synthesis inhibition and the inhibition of macromolecular synthesis which may also be linked to cell membrane damage (de Leon and Moujir, 2008).…”

“…However, previous antibacterial studies on RA3 and RA5 by Penduka et al (2014) and Mosa et al (2014b) showed some MIC values within the ranges of 100-1000 µg/ml. Interestingly, the study by Mosa et al (2014b) similarly proved RA3 and RA5 to having a high MIC value of above 1000 µg/ml against E. coli bacteria.…”

“…Ciprofloxacin is a fluoroquinolone antibiotic, which acts through inhibition of the enzymes topoisomerase II (DNA gyrase) and topoisomerase IV, which are required for bacterial DNA replication (Hooper, 2000). In contrast, pent-acyclic triterpenes have been shown in some interaction studies to have synergistic activities with penicillin G (Penduka et al, 2014), vancomycin (Chung et al, 2011) and methillicin (Chung et al, 2011), which are all antibiotics that inhibit cell wall biosynthesis, which may suggest that pent-acyclic triterpenes work synergistically or favourably with antibiotics that inhibit cell wall biosynthesis in comparison to those that inhibit DNA replication.…”

“…The interactions of the triterpenes and ciprofloxacin were interpreted by using the fractional inhibitory concentration (FIC) indices, which were determined using the checkerboard method according to the descriptions of Penduka et al (2014). Serial dilutions of the antimicrobial combinations in double strength Mueller-Hinton broth were performed in 96 well microtiter plates to make different test concentrations.…”

Techniques for the analysis of pentacyclic triterpenoids in medicinal plants

“…In recent years, the medicinal values of pentacyclic triterpenoids have been increasingly recognized and studied because of their anti-inflammatory [39], hypoglycemic [1,30], antibacterial [40,41], antioxidant [42,43], antitumor [44][45][46], antiproliferative [47], anti-HIV [48][49][50], antitrypanosomal [51], antileishmanial [52,53], anti-arthritic [54], hepatoprotective [55,56], cardiovascular [57], and immunological adjuvant [58] activities. In the past decade, numerous reports indicated that pentacyclic triterpenoids exhibit various bioactivities.…”