Synergy between Ursolic and Oleanolic Acids from Vitellaria paradoxa Leaf Extract and β-Lactams against Methicillin-Resistant Staphylococcus aureus: In Vitro and In Vivo Activity and Underlying Mechanisms

Abstract

Combining antibiotics with resistance reversing agents is a key strategy to overcome bacterial resistance. Upon screening antimicrobial activities of plants used in traditional medicine, we found that a leaf dichloromethane extract from the shea butter tree (Vitellaria paradoxa) had antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) with further evidence of synergy when combined with β-lactams. Using HPLC-MS, we identified ursolic (UA) and oleanolic acids (OA) in leaves and twigs of this species, and quantified them by HPLC-UV as the major constituents in leaf extracts (21% and 6% respectively). Both pure triterpenic acids showed antimicrobial activity against reference and clinical strains of MRSA, with MICs ranging from 8–16 mg/L for UA to 32–128 mg/L for OA. They were highly synergistic with β-lactams (ampicillin and oxacillin) at subMIC concentrations. Reversion of MRSA phenotype was attributed to their capacity to delocalize PBP2 from the septal division site, as observed by fluorescence microscopy, and to disturb thereby peptidoglycan synthesis. Moreover, both compounds also inhibited β-lactamases activity of living bacteria (as assessed by inhibition of nitrocefin hydrolysis), but not in bacterial lysates, suggesting an indirect mechanism for this inhibition. In a murine model of subcutaneous MRSA infection, local administration of UA was synergistic with nafcillin to reduce lesion size and inflammatory cytokine (IL-1β) production. Thus, these data highlight the potential interest of triterpenic acids as resistance reversing agents in combination with β-lactams against MRSA.

Ursolic acid inhibits colistin efflux and curtails colistin resistant Enterobacteriaceae

“…Ursolic and oleanic acids were earlier reported to synergize with beta lactam antibiotics against gram positive pathogens S. aureus, S. epidermidis and Listeria monocytogenes (Kurek et al 2012). In a recent interesting study, ursolic and oleanic acids present in dichloromethane extract of shea butter tree were shown to synergize with ampicillin and oxacillin against MRSA and cause reversion of MRSA phenotype which was attributed to delocalization of PBP2 from the septal division site leading to disturbance in peptidoglycan synthesis, in addition the triterpenoids also caused indirect inhibition of β-lactamases and reversed β-lactam resistance in MRSA (Catteau et al 2017). To the best of our knowledge, ursolic acid was not reported to interact synergistically with colistin in bacteria.…”

Synergy and antagonism in natural product extracts: when 1 + 1 does not equal 2

“…In a recent study, Catteau et al . 138 found that a dichloromethane extract of shea butter tree leaves ( Vitellaria paradoxa C.F. Gaertn.…”

“…V. paradoxa constituents ursolic acid and oleanolic acid were found identified as the constituents responsible for this synergistic activity. 138…”

Unraveling Plant Natural Chemical Diversity for Drug Discovery Purposes

“…Some examples of screening results of extracts with those approaches (Atanasov et al, 2015) can be mentioned here, but being exhaustive is impossible, as literally hundreds of such tests were performed [e.g. from our laboratories (Bousserouel et al, 2005;Lautié et al, 2008;Litaudon et al, 2009a;Litaudon et al, 2009b;Columba-Palomares et al, 2015;Catteau et al, 2017;Olivon et al, 2018) and from hundreds of others]. Some examples reported recently are given in Table 1 of the inhibitory activities of plant extracts on specific enzymes.…”