*4.1.3.3. Compounds with antimicrobial activity*

Looking at plant extract to find novel antimicrobial compounds is interesting for clinical microbiologists for two reasons, namely, it is very likely that these phytochemicals will be sooner rather than later prescribed as antimicrobial drugs, and the public is becoming increasingly aware of problems with the over prescription and misuse of traditional antibiotics [123]. It is reported that, on average, two or three antibiotics derived from microorganisms are launched each year [124]. Phytochemicals with an antimicrobial activity can be divided into several categories, most of which were already described above. These include phenolics, terpenoids, essential oils and alkaloids [123]. Among the other ones, we will briefly review also the lectins and polypeptides, as well as polyacetylenes.

*4.1.3.1. Alkaloids*

132 Herbal Medicine

*4.1.3.2. Resins*

safe, but contact allergy may occur [116].

*4.1.3.3. Compounds with antimicrobial activity*

Alkaloids are heterocyclic compounds that contain a nitrogen atom in at least one of the heterocycles [108]. They usually have various potent biological activities and are of bitter taste [109]. Some synthetic compounds of similar structure are also termed alkaloids. They are not that common in the plant kingdom, are represented by diverse chemical structures, and almost all show interesting properties for therapeutic use [110]. Alkaloids are produced also by other organisms including bacteria, fungi and animals [109]. Although alkaloids are not the first choice of chemicals to be used in relation to wound treatment, there are still some interesting plants that need further analysis due to their already proven potential for this purpose. Among the plants that produce alkaloids with potential beneficial effects on wound healing are the *Papaveraceae* (poppy family) and *Berberidaceae* (barberry family) families [111]. Both produce isoquinoline alkaloids that possess a range of biochemical effects relevant for medical use (e.g. inhibition of pain, growth inhibition of cancer cell growth, and growth of bacterial cells) [111]. Among other indirectly related beneficial properties are also the stimulation of bone marrow leucocytes, which modulate the inflammation phase of wound healing [112].

This group of plant-derived compounds presents a complex mixture of lipid-soluble chemicals [113]. These can be both non-volatile (e.g. diterpenoid and triterpenoid compounds) and volatile (mono- and sesquiterpenoids) [114]. Resins are most commonly found in nature as part of various wood-derived structures, although they are also present in herbaceous plants [115]. Among their common properties are a general stickiness, whereas their fluidity depends on the contents of volatile compounds [115]. When exposed to air they harden. Among their beneficial biological activities for wound healing are the antimicrobial activity, but their actions depend on the composition of the chemical mixture. Resins are generally

The common structural precursor of terpenoids is the five-carbon building block isoprene [117]. Monoterpenoids are formed of two isoprene units, whereas sesquiterpenoids consist of three units. Both mentioned groups are commonly denoted as low-molecular-weight terpenoids, which are one of the most varied groups of plant products that include more than 25,000 compounds [118]. The phenylpropanoid group of terpenoids is less common and is based on a nine-carbon skeleton, whereas their synthesis pathway differs from the other terpenoids [119]. Compounds of all three mentioned groups have often strong odours and flavours, which is related to their properties (e.g. the lipophilicity and volatility) [120]. Since they exhibit various biological activities, they are found in several herbal remedies [121]. Of particular importance in relation to wound healing are their antibacterial and antiviral effects, whereas they possess also other activities like the antineoplastic activity, as well as stimulation gastrointestinal tract [118]. They are not toxic unless they are concentrated as volatile oils

[122]. The plant family best known for these compounds is *Lamiaceae* (thyme family).

Looking at plant extract to find novel antimicrobial compounds is interesting for clinical microbiologists for two reasons, namely, it is very likely that these phytochemicals will be First antimicrobial peptides were reported back in 1942 [123]. Mostly, these compounds are positively charged and include disulphide bonds in their structure [125]. One of the known possible mechanism of actions involves the formation of ion channels in the microbial membrane [125], while the other is related to a competitive inhibition of adhesion of microbial proteins to host polysaccharide receptors [126]. Some of the most important subgroups of antimicrobial peptides include thionins, which are toxic to yeasts and Gram-negative and Gram-positive bacteria [125].

Polyacetylenes are another group of potential antimicrobial compounds with interesting properties. The compound 8S-heptadeca-2(Z),9(Z)-diene-4,6-diyne-1,8-diol was shown to be effective against *S. aureus* and *B. subtilis* but not to Gram-negative bacteria or yeasts [127]. In Brazil, acetylene compounds and flavonoids derived from single plant extracts traditionally are used for treatment of malaria fever and liver disorders [128].
