**1.5 Chemical nature of antibacterial agents**

A large number of pharmacologically active substances like sesquiterpenes (Abraham, 2001), hydroquinones (Mothana et al., 2000), polysaccharides and complexes of polysaccharide-peptide (Liu, 1999), lanostanoide triterpenoids (Shiao, 1992, Leon et al., 2004) steroids (Smania, 2003), nucleosides, alkaloids and vitamins (Paterson, 2006) from fruitbodies of polypore fungi have been detected. Recent studies pronounced phenolic compounds (Turkoglu et al., 2007, Paterson, 2006, Ribeiro et al., 2007) as the main active antioxidative components in fungal extracts (Kityberger et al., 2007; Barros et al., 2007). It is assumed that antibacterial effects exhibited by fungal extracts of different polarites could be related to an overall effect of phenolic compounds (e.g. phenolic acids: caffeic acid, ellagic acid; flavonoids, hydroquinones) detected in similar extracts of the species *G.lucidum*, *F.velutipes*, *P.ostreatus* or organic acids (oxalic, malic) previously detected in *L. sulphureus* and *F. hepatica*, as well as terpenoids.
