Antibiotic adjuvants from Buxus sempervirens to promote effective treatment of drug-resistant Staphylococcus aureus biofilms

Abstract

Plants have been long scrutinized in the quest for new antibiotics, but no strong antibiotic molecule was ever found. Evidences exist that most phytochemicals have a regulatory or adjuvant effect on other antibacterial compounds, thus promoting a greater therapeutic effect. The current study assessed twenty-eight plants from different families for their antibacterial activity and as adjuvants in antibiotic therapy against Staphylococcus aureus, including methicillin-resistant S. , respectively. Non-antibacterial plants were assessed in combination with ampicillin, oxacillin, ciprofloxacin, erythromycin and tetracycline by a modified disc diffusion test. Methanolic extracts of Acacia dealbata, Prunus spp. plants, Centaurea nigra, Eupatorium cannabium and Buxus sempervirens showed a potentiating effect mostly of ciprofloxacin, erythromycin and tetracycline. B. sempervirens was selected for its potentiating activity and applied against S. aureus biofilms. B.sempervirens (1 g L -1 ) was able to cause an 88% reduction of S. aureus within 1 h exposure. Further phytochemical investigation of B. sempervirens allowed to identify betulinic acid as a major component, together with other triterpenoids. Betulinic acid and other common terpernoids -lupeol, betulin, hederagenin, ursolic acid and oleanolic acid, were tested for antibacterial and antibiotic-potentiating activities. Among the tested compounds, oleanolic acid and ursolic acid -were highlighted, showing MIC of 62.5 and 15.6 mg L -1 , respectively, against S. aureus. Additionally, oleanolic acid showed synergism when combined with tetracycline and erythromycin and caused biofilm reductions of 70, 81 and 85% when applied at ½ MIC, MIC and 2 × MIC, respectively. IntroductionTwo major circumstances have accentuated the quest for new antibacterial agents and alternative therapies in the last decades. Primarily, because microbes, due to their incredible and innate adaptability, seem to have at least equal chances for survival as scientists and pharmaceutical industries develop methods to kill them. 3 Multidrug-resistant (MDR) bacteria are responsible for a large number of nosocomial but also community-acquired infections and are spreading all over the globe. 4 Additionally, the limitation of our current arsenal of effective antibiotics accompanied by the lack of new antimicrobial alternatives are prompting the beginning of the "post-antibiotic era", which threats all the achievements of modern medicine.Since the beginning of mankind plants were undoubtedly the most important source of therapeutic remedies with an enormous range of applications. The earliest records of natural products were depicted from Mesopotamia (2600 B.C.) and included oils from cypress (Cupressus sempervirens) and myrrh (Commiphora species), which are still used today to treat coughs, colds and inflammation. 5 Many plant extracts and their phytochemical constituents are known to have antimicrobial activities. 6 However, it can be rapidly established that this effort of finding individual active anti...

Looking to nature for a new concept in antimicrobial treatments: isoflavonoids from Cytisus striatus as antibiotic adjuvants against MRSA

“…striatus leaves, flowers and twigs were applied at 0.5 mg/mL. Inhibition zones obtained with the combinations (IZD c ) over antibiotic-single activity (IZD a ) are given and the combinations are classified as: (—) indifferent (IZD c – IZD a < 4 mm); (A) additive (4 ≤ IZD c – IZD a < 6 mm); and (P) potentiation (IZD c – IZD a ≥ 6 mm) 20 , 35 , 36 . Data are means and SD from at least three independent experiments.…”

“…This method is most suitable for testing plant extracts, as it allows a better visualization and detection of the potentiating effects. The test was performed as described in previous studies 20 , 35 , 36 . Dried C .…”

“…The antibiotic-potentiating activity of C . striatus extracts was categorized, as described in previous studies 20 , 35 , 36 , into three classes according to the ratio of the increase of the IZD produced by the antibiotic in the presence of the plant extracts to that obtained with the antibiotic alone (on simple MH agar plates): 1 – indifferent (IZD combination – IZD antibiotic < 4 mm); 2 – additive (4 ≤ IZD combination – IZD antibiotic < 6 mm); and 3 – potentiation (IZD combination – IZD antibiotic ≥ 6 mm) of inhibition of growth of S . aureus .…”

“…Cytisus striatus (Fabaceae), commonly known as Portuguese broom, a very abundant shrub in the Iberian Peninsula, was selected from among several other plants 20 for its strong potentiating activity of ciprofloxacin and erythromycin against one of the most menacing bacterial strains, MRSA, which causes serious, invasive and life-threatening infections worldwide 21 . MRSA strains belonging to CC8, including the common ST239 found in Asia and a Dutch ST8-MRSA, were tested.…”

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

“…Our results are also limited to the combination of UA and OA with β-lactams. Combinations with other classes of antibiotics have already been described as synergistic for glycopeptides, tetracyclines or macrolides [ 20 , 47 ] or additive for fluoroquinolones against different Staphylococcus aureus strains [ 48 , 49 ]. The mechanism of these interactions has not been elucidated yet but should implicate other mechanisms than those discovered here, though also possibly related to their interaction with membranes.…”