The antibacterial activity of a series of simple coumarins was evaluated against 8 microor ganisms, including three Gram-positive (Staphylococcus aureus, beta-hemolytic Streptococcus and Streptococcus pneum oniae) and five Gram-negative bacteria (Escherichia coli, Klebsiella pneum oniae, Pseudom onas aeruginosa, Proteus mirabilis and H aemophilus influenzae), using the microdilution broth method. The coumarins tested showed broad diversity regarding growth inhibitory activity with minimum inhibitory concentrations ranging from 0.9 to >12.4 (j.M . This study, presenting the first systematic analysis of structure-activity relationships among this group of coumarins, revealed some interesting structural requirements. While coumarins with a methoxy function at C-7 and, if present, an OH group at either the C-6 or C-8 position are invariably effective against the spectrum of tested standard bacteria (Gramnegative microorganisms including the Gram-positive bacterium Staphylococcus aureus), the presence of an aromatic dimethoxy arrangement is apparently favourable against those mi croorganisms which require special growth factors (beta-hemolytic Streptococcus, Streptococ cus pneum oniae and Haem ophilus influenzae). A combination of these structural features, two methoxy functions and at least one additional phenolic group as reflected by the highly oxygenated coumarins, identify promising candidates with antibacterial broad-spectrum ac tivity.
The antibacterial activity of extracts and isolated constituents (scopoletin, umckalin, 5,6,7-trimethoxycoumarin, 6,8-dihydroxy-5,7-dimethoxycoumarin, (+)-catechin, gallic acid and its methyl ester) of Pelargonium sidoides and Pelargonium reniforme (Geraniaceae), plant species used in folk medicine by the Southern African native population, was evaluated against 8 microorganisms, including 3 Gram-positive (Staphylococcus aureus, Streptococcus pneumoniae, and beta-hemolytic Streptococcus 1451) and 5 Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Haemophilus influenzae). Minimum inhibitory concentrations (MICs) varied with the preparation of the extracts and microorganisms tested, from about 0.6 mg/ml for aqueous phases to over 10 mg/ml for crude Pelargonium extracts. With the exception of the ineffective (+)-catechin, all the potentially active compounds exhibited antibacterial activities with MICs of 200-1000 micrograms/ml. The results provide for a rational basis of the traditional use of the titled Pelargonium species.
Pelargonium species contribute significantly to the health care of a large population in the Southern African region, as part of a long-standing medical system intimately linked to traditional healing practices. Most notably, extracts of the roots of P. sidoides have commonly been applied for the treatment of dysentery and diarrhoea but only occasionally for respiratory complaints. Clinical trials have shown that a modern aqueous-ethanolic formulation of P. sidoides extracts (EPs® 7630) is an efficacious treatment for disorders of the respiratory tract, for example bronchitis and sinusitis. It should be noted that EPs® 7630 is the most widely investigated extract and therefore is the focus of this review. In order to provide a rationale for its therapeutic activity extracts have been evaluated for antibacterial activity and for their effects on non-specific immune functions. Only moderate direct antibacterial capabilities against a spectrum of bacteria, including Mycobacteria strains, have been noted. In contrast, a large body of in vitro studies has provided convincing evidence for an anti-infective principle associated with activation of the non-specific immune system. Interestingly, significant inhibition of interaction between bacteria and host cells, a key to the pathogenesis of respiratory tract infections, has emerged from recent studies. In addition, antiviral effects have been demonstrated, including inhibition of the replication of respiratory viruses and the enzymes haemagglutinin and neuraminidase. Besides, an increase of cilliary beat frequency of respiratory cells may contribute to the beneficial effects of P. sidoides extracts. This example provides a compelling argument for continuing the exploration of Nature and traditional medical systems as a source of therapeutically useful herbal medicines.
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