Evaluation of the antibacterial synergism of two plant extracts belonging to Bignoniaceae family and development of a topical formulation

Abstract Fridericia caudigera and Cuspidaria convoluta (Bignoniaceae) species, which grow in the northwest of Argentina, have shown antibacterial effect against strains isolated from skin infections, and each one displayed synergism with commercial antibiotics. The aims of this work were to evaluate the antibacterial activity and toxicity of the combination of these two plant species, and to design a stable gel for topical use including the blend of extracts. The combination of extracts was evaluated for synergistic effects (chequerboard assay), genotoxicity (Ames test) and cytotoxicity (Artemia salina test). A gel was subsequently formulated with the combination of extracts using carboxymethylcellulose as a polymer. The following physico- chemical characteristics of the gel formulation: pH, viscosity, spreadability and total phenol content, as well as resistance to severe temperature changes, biological activity (diffusion in agar), in vitro permeation (Franz cells) and primary dermal irritation (Draize test) were analyzed. The combination of extracts showed a synergistic effect on pathogenic bacteria and was not toxic in the in vitro tests. The gel was stable and retained the antimicrobial activity of the original extracts. The formulation proposed in this work could constitute an alternative for primary skin infections since it proved to be safe for topical administration.

In vitro antioxidant, antilipoxygenase and antimicrobial activities of extracts from seven climbing plants belonging to the Bignoniaceae.

OBJECTIVES: This study aimed to evaluate the in vitro antioxidant capacity, to determine the anti-inflammatory effect due to lipoxygenase inhibition and to test the antimicrobial activity of ethanolic extracts from leaves of seven climbing species belonging to the Bignoniaceae family. These species are Adenocalymma marginatum (Cham.) DC., Amphilophium vauthieri DC., Cuspidaria convoluta (Vell.) A. H. Gentry, Dolichandra dentata (K. Schum.) L. G. Lohmann, Fridericia caudigera (S. Moore) L. G. Lohmann, Fridericia chica (Bonpl.) L. G. Lohmann and Tanaecium selloi (Spreng.) L. G. Lohmann. METHODS: The antioxidant activity was evaluated using three methods, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and ferric reducing antioxidant power. Lipoxygenase-inhibiting activity was assayed spectrophotometrically; the result was expressed as percent inhibition. The antimicrobial activity was assessed using the agar disk diffusion method. Minimal inhibitory concentration (MIC) and minimal bactericidal/fungicidal concentration were also determined for each extract against 12 pathogenic bacterial strains of Staphylococcus aureus and seven fungal strains of the Candida genus. The identification of the major compounds present in the most promising extract was established by high-performance liquid chromatography-tandem mass spectrometry. RESULTS: C. convoluta, F. caudigera, and F. chica exhibited the best antioxidant activity by scavenging DPPH and ABTS+ radicals and reducing Fe3+ ion. These extracts showed a notable inhibition of lipoxygenase. F. caudigera was found to have the lower MIC value against S. aureus strains and six Candida species. The extracts of F. caudigera and C. convoluta were active even against methicillin-resistant S. aureus. C. convoluta had higher total phenol content, better antioxidant activity and superior anti-inflammatory and antimicrobial activity. The main phenolic compounds found in this extract were coumaric and hydroxybenzoic acid derivatives and glycosylated and nonglycosylated flavones. CONCLUSION: Most of the extracts exhibited antioxidant activity as well as in vitro inhibition of lipoxygenase. The excellent antimicrobial activity of T. selloi and F. chica supports their use in traditional medicine as antiseptic agents. The extracts of F. caudigera and C. convoluta, both with notable biological activities in this study, could be used as herbal remedies for skin care. In addition, this study provides, for the first time, information about phenolic compounds present in C. convoluta.

In vitro antimicrobial activity of 20 selected climber species from the Bignoniaceae family.

Hydroalcoholic and aqueous extracts of some climber species from the Bignoniaceae family that grow in the north of Argentina were evaluated for in vitro antibacterial activity against Gram-positive and Gram-negative strains. By means of bioautography and disc diffusion methods, it could be determined that all infusions were not active, whereas the hydroalcoholic extracts of seven species were able to inhibit bacterial growth. The minimum inhibitory concentration and minimum bactericidal concentration observed were between 62.5 and 1000 µg gallic acid equivalent (GAE)/mL and between 125 and 1000 µg GAE/mL, respectively. The tested extracts were more active against Gram-positive microorganisms. Time-kill experiments indicated that all extracts have bacteriostatic activity. Phytochemical screening showed the presence of terpenoids, phenols and flavonoids. The amount of phenolic compounds and flavonoids was higher in tinctures when compared with infusions. These results suggest the presence of antibacterial substances in the hydroalcoholic extracts, which could be used for the treatment of infections.