Flavonoids antimicrobial activities

Fig. 4. Comparison of the two signal-reaction chains leading either to the UV light-induced formation of flavonoids or to the elicitor-induced formation of furanocoumarins and related compounds with antimicrobial activity. From Hahlbrock et al. (1985). PR -proteins are pathogenesis-related proteins.

Some phenolic acids such as ellagic acid can be used as floral markers of heather honey (Cherchi et al., 1994 Ferreres et al., 1996a,b), and the hydroxyciimamates (caffeic, p-coumaric, and ferulic acids) as floral markers of chestnut honey (Cherchi et al., 1994). Pinocembrin, pinobanksin, and chrysin are the characteristic flavonoids of propolis, and these flavo-noid compounds have been found in most European honey samples (Tomas-Barberan et al., 2001). However, for lavender and acacia honeys, no specific phenolic compoimds could be used as suitable floral markers (Tomas-Barberan et al., 2001). Other potential phytochemical markers like abscisic acid may become floral markers in heather honey (Cherchi et al., 1994). Abscisic acid was also detected in rapeseed, lime, and acacia honey samples (Tomas-Barberan et al., 2001). Snow and Manley-Harris (2004) studied antimicrobial activity of phenolics. 

The purpose of this review is to discuss recent developments related to the chemistry and medicinal properties of natural flavonoids. This review covers more recent reports (2005 to the present date) of antimicrobial activity of flavonoids (antibacterial and antifungal), as well as the antiviral activity of these compounds. 

Pistelli L, Bertoli A, Noccioli C, Mendez J, Musmanno RA, Maggio T, Coratza G. (2009) Antimicrobial activity of Inga fendleriana extracts and isolated flavonoids. Nat Prod Commun 4 1679-1683. 

Habbu PV, Mahadevan KM, Shastry RA, Manjunatha H. (2009) Antimicrobial activity of flavonoid sulphates and other fractions of Argyreia speciosa (Burm. f.) Boj. Indian J Exp Biol 47 121-128. 

Da Silva MA, Cardoso CA, Vilegas W, Dos Santos LC. (2009) High-performance liquid chromatographic quantification of flavonoids in Eriocaulaceae species and their antimicrobial activity. Molecules 14 4644-4654. 

Mbaveng AT, Ngameni B, Kuete V, Simo IK, Ambassa P, Roy R, Bezabih M, Etoa EX, Ngadjui BT, Abegaz BM, Meyer JJ, Lall N, Beng VP. (2008) Antimicrobial activity of the crude extract and five flavonoids from the twigs of Dorstenia barteri (Moraceae). J Ethnopharmacol 116 483 89. 

Flavonoid glycosides and their esters are an important group of natural compounds isolated from plants. They are widely used in pharmaceutical, cosmetic, and food preparations, and it is therefore not surprising that the search for new derivatives with improved antioxidant and antimicrobial activity, or-more sim-ply-with more suitable physico-chemical properties for specific applications (i.e., increased stability and/or solubility), has identified enzyme-catalyzed regioselective esterification as a particularly promising approach to the target molecules [21a],... 

Fig. 2 Chemical structures of the flavonoid derivatives with antimicrobial activity...

Secondary compounds known for their antimicrobial activity include many phenolics (e.g., flavonoids, isoflavones, and simple phenolics), glu-cosinolates, nonproteinogenic amino acids, cyanogenic glycosides, acids, aldehydes, saponins, triterpenes, mono- and disesquiterpenes, and last but not least, alkaloids (4,17,42,149,312). 

Cushnie, T.P.T. Lamb, A.J. 2005. Antimicrobial activity of flavonoids. Int. J Anti-microb. Agents 26 343-356. 

Flavonoids are natural polyphenolic substances widely distributed in the different parts of plants such as fruits, bark, stems, roots, leaves and flowers. Structurally they are characterized by a pyran ring or a similar structure of three carbons. These polyphenolic compounds are well known for displaying a remarkable spectrum of biological activities, including antibacterial and antifungal properties. In the Anthemideae tribe, some of these compounds were isolated by bioassay-guided fractionation, after previously detecting antimicrobial activity on the part of the plant. 

Zhu et al. [222] examined the antimicrobial activities of four flavonoids, luteolin-7-rutinoside, cynaroside. Fig. (31), apigenin-7-rutinoside and apigenin-7-G-P-Z)-glucopyranoside, isolated from the n-butanol soluble fraction of artichoke leaf extracts (Cynara scolymus). The compounds showed activity against most of the tested organisms, and were more effective against fungi than bacteria. The MIC values of these compounds were between 50 and 200 )J.g/ml. 

From the drug flos Calendulae Calendula officinalis L.), two flavonoids were isolated by bioassay-guided fractionation [226]. They showed potent antimicrobial activity against the following microorganisms Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, Candida monosa and Sarcinia lutea. 

The antimicrobial activity of another flavonoid, apigenin, Fig. (33) isolated from Moquinia kingii Gamerro, was also screened using 22 strains including Gram +) and (-) bacteria and the yeasts Candida albicans and Candida tropicalis [227]. The compound was active for both activities. 

Other flavonoids from the Anthemideae tribe also showed a broad spectrum of antimicrobial activity. Crude extracts of Haplopappus sonorensis (A. Gray) S.F. Blake showed activity against Mycobacterium tuberculosis [228], 5-hydroxy-3,7,4 -trimethoxyflavone, 5,7-dihydroxy-3,4 -dimethoxyflavone (ermanin), Fig. (34) and 5,4 -dihydroxy-3,7-dimethoxyflavone were identified by assay-guided fractionation, as the antimycobacterial principles. The flavonoid ermanin, Fig. (34) was the most active compound. 

The antimicrobial activity of luteolin. Fig. (35), a flavonoid isolated from Wedelia paludosa was also evaluated [205]. The compound showed activity towards the dermatophytes Epidermophyton floccosum. Trichophyton rubrum and Trichophyton mentagrophytes. 

The antimicrobial polymethylated flavones, 5-hydroxy-3,6,7,8,4 -pentamethoxyflavone, 5-hydroxy-3,6,7,8-tetramethoxyflavone and 5,6-dihydroxy-3,7-dimethoxyflavone, have been isolated from Gnaphalium affine D Don. [229,230], These flavonoids showed antimicrobial activity against Spodoptera litura. Structure-activity studies suggested the importance of the 6-position substitution of the flavonoid however, hydrophilic substituents decreased the activity. The flavonoid 8-0-(2-methyl-2-butenoyl)-5,7-dihydroxy-3-methoxyflavone isolated from Gnaphalium robustum L. also inhibited the growth of Escherichia coli [231]. 

Elaeodendron transvaalensis (Brrrtt Davy) ingwavuma, bttshveld saffron] (Celastraceae) stem bark concoction is ttsed as an emetic. The stem bark contains alkaloids, flavonoids, glycosides, polyphenols, saponirts and tannirrs (15). The plant is also used to treat sexually transmitted diseases and its extraet exhibits antimicrobial activity (27). 

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