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.

Morphoanatomical and histochemical characterization of Larrea species from Northwestern of Argentina

Abstract Larrea divaricata Cav., L. cuneifolia Cav. and L. nitida Cav., Zygophyllaceae, are evergreen xerophytic shrubs occurring in Northwestern Argentina used in traditional medicine. The aim of this work was to characterize the morphology, anatomy and histochemistry of the vegetative organs of three Larrea species by light and scanning electron microscopy in order to provide supporting data for their correct identification and to determine the site of synthesis and accumulation of its main active compounds. The shape, number and percentage of coalescence of leaflets, presence or absence of mucrones and rachis and the shape of the stipules represented the main botanical differences between the studied Larrea species. Anatomically three species presented amphystomatic leaves, with thick resinous slightly striated cuticle with resinous deposits, polygonal epidermal cells with straight anticlinal walls, ciclocytic, brachy-paracytic and paracytic stomatal types, non-glandular trichomes and isolateral mesophyll. The position and abundance of the sclerenchyma at the mid vein and petiole transection allows the differentiation of the three species, been more abundant in L. cuneifolia. Secondary phloem and parenchyma cells presented abundant calcium oxalate druses and solitary rhomboidal crystals. Epidermal cells and cuticle layer of leaflets and stipules of the three species presented amber resin deposits and content which stained positively for polysaccharides, phenolic compounds, flavonoids and tannins, while mesophyll palisade cells showed small refracting droplets stained positively for lipophilic substances.

Actividad antimicrobiana de plantas medicinales argentinas sobre bacterias antibiótico-resistentes / Antimicrobial activity of Argentine medicinal plants on antibiotic-resistant bacteria

El propósito del presente trabajo fue determinar la potencia antimicrobiana de extractos alcohólicos de plantas utilizadas popularmente en Argentina como antisépticos y antiinflamatorios: Dasyphyllum diaconthoides, Erythrina cristagalli, Larrea cuneifolia, Larrea divaricata, Phytolacca dioica, Pithecoctenium cynanchoides, Prosopanche americana, Schinus molle, Schkuhria pinnata, Senna aphylla y Solidago chilensis. La inhibición del crecimiento bacteriano se determinó a través de ensayos de difusión en agar, macrodilución en medio sólido y microdilución en medio líquido frente a 47 aislamientos clínicos multirresistentes a antibióticos, obtenidos de pacientes de un hospital de Tucumán, Argentina: Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterobacter cloacae, Serratia marcescens, Morganella morganii, Acinetobacter baumannii, Pseudomonas aeruginosa, Stenotrophomonas maltophilia. De acuerdo con los valores de concentración inhibitoria mínima (CIM), tres de las once especies ensayadas fueron las más activas: L. divaricata, L. cuneifolia, y S. aphylla (CIM de 25 a 200 µg/mL). P. mirabilis, A. baumanni y S. maltophilia fueron las cepas más susceptibles con valores de CIM entre 25 y 50 µg/mL seguido por P. aeruginosa con valores de CIM de 50 a 100 µg/mL. Los valores de concentración bactericida mínima (CBM) fueron semejantes o dos veces superiores a los valores de CIM. Mediante ensayos bioautográficos se comprobó que los extractos más activos presentaban al menos dos principios antimicrobianos. Análisis fitoquímicos indican que estos compuestos son de naturaleza fenólica. Los resultados obtenidos justificarían el uso de estos extractos para el tratamiento de infecciones bacterianas, especialmente aquellas de origen dérmico.

The present study was conducted to investigate antimicrobial activity of alcoholic extracts of Argentine medicinal plant species (Dasyphyllum diacanthoides, Erythrina cristagalli, Larrea cuneifolia, Larrea divaricata, Phytolacca dioica, Pithecoctenium cynanchoides, Prosopanche americana, Schinus molle, Schkuhria pinnata, Senna aphylla and Solidago chilensis) against multidrug resistant human pathogen gram negative bacteria isolated from a Hospital in Tucumán, Argentina. Inhibition of bacterial growth was investigated using disc diffusion, agar macrodilution and broth microdilution methods against multiresistant clinical isolates of nine different specie of gram negative bacteria: Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterobacter cloacae, Serratia marcescens, Morganella morganii, Acinetobacter baumannii, Pseudomonas aeruginosa, Stenotrophomonas maltophilia. A significant antimicrobial activity was found in three of the eleven plant species studied. Based on minimal inhibitory concentration (MIC) values, three plant species, L. divaricata, L. cuneifolia, and S. aphylla were the most potent ones with MIC values between 25-200 µg/mL. Overall, P. mirabilis, M. morganii and P. aeruginosa isolates were the most susceptible to these extracts with MIC values of 25 to 50 µg/mL. All extracts showed significant inhibitory activities on bacteria growth in a dose phenolic compound-dependent fashion. The minimal bactericidal concentration (MBC) values were identical to the MIC values or twofold higher than the corresponding MIC. Contact bioautography indicated that crude extracts possess several major antibacterial components. Phytochemical screening showed that the bioactive compounds correspond to polyphenols. Investigations are in progress to purify the bioactive principles.