Taxonomie, chimiotaxonomie et évaluation des activités antifongiques et antibactériennes de quelques Basidiomycètes supérieurs (Agaricales et Polyporales) du Cameroun et de la R.D. Congo

Abstract

In spite of numerous works carried out during the past three decades on the mycological flora of central Africa, this flora is very little known in several countries of this subregion of Africa and particularly in Cameroon and the D.R. of Congo (ex Zaïre). Therefore, in order to contribute improving the state of knowledge of this flora in these two countries and also test in vitro some of their potential therapeutic properties, a total of 182 specimens of higher Basidiomycetes belonging to the Agaricales, Boletales and Polyporales were collected in the two contries during the years 2017 and 2018 and thereafter encoded from DM 1161 to DM 1251 for the Polyporales, DM 1261 to DM 1336- DM 1718 to DM 1730 for the Agaricales and DM 1341 to DM 1342 for the Boletales and conserved in the Mycological Herbarium of the University of Yaoundé 1 (HUY1). Of the 182 specimens, 35 have been described using the tools of conventional taxonomy, nine new species and two new forms of Termitomyces were identified. They include T. fombapei sp. nov., T. mboukouïna sp. nov., T. mbongonensis sp. nov., T. africana sp. nov., T. subeurhizus sp. nov., T. bruneogriseus sp. nov., T. tribasidiatus sp. nov., T. melongii sp. nov., T. congolensis sp. nov. for the new species and Termitomyces mammiformis f. cameroonensis f. nov. coupled with T. eurhizus f. polycystidiatus f. nov. for the 2 new forms. The taxonomic study also led to the description of two new species of wood fungi belonging to the Polyporaceae which are Aporpium cameroonensis sp. nov. and Perenniporia nigra sp. nov. Concerning chemotaxonomy, the tools of CCM and GC-MS enabled a detailed phytochemistry study of some species of Hymenochaetaceae belonging to the Polyporales and including Coltricia fragilissima, Phellinus extensus, P. gilvus, P. pachyphloeus, P. senex, as well as some Pleurotaceae including Pleurotus tuber-regium and P. sajor-caju. The comparison of chemical constituents of these species led to establish that the undetermined specimen of Polyporales DM 1069 is close to Phellinus senex, whereas the specimens DM 703, DM 1073 and DM 1588 could be potential new species or forms of Phellinus provided some additional analysis of confirmation eventually coupled to DNA phylogeny are carried out. By comparison to results of previous studies carried out by other authors, the following chemical constituents identified in our local species, namely : 1-Hexadecene ; (Z)-7-Hexadecene, ; Hexadecane, , (E)-5-Octadecene ; 1-Docosene ; Hexadecanoic Acid , ethyl ester ; (E)-9-Octadecenoic Acid, ethyl ester ; Tetradecanoic Acid, ethyl ester ; Eicosane ; Docosane and , (E)-5-Eicosene. According to the above mentioned studies, these chemical constituents show numerous therapeutic properties including antimicrobial, antioxydative, hypoglycemic, antiiflammatory, antidiarrhoea, hypocholesteromic, antitumoral, antitetanic and these properties are potentially also present in our local mushrooms species For microbiological studies, antifungal and antibacterial properties of 7 species of Macromycetes of which 5 Hymenochaetaceae (Phellinus extensus, P. gilvus, P. pachyphloeus, P. senex, Coltricia fragilissima) and 2 Pleurotaceae (Pleurotus sajor-caju and Pleurotus tuber regium (basidiocarp and sclerotia) were ascertained using the microdilution method and determination of the Minimal Inhibitory Concentration (MIC). The test was carried out on 11 strains of bacteria including Bacillus subtilis, Enterococcus faecalis, Staphylococcus epidermidis, Enterobacter cloacae, Klebsiella aerogenes, Staphylococcus aureus, Mycobacterium smegmatis, Proteus vulgaris, Klebsiella oxytoca, Proteus mirabilis, Escherichia coli; and 3 strains of human pathogenic fungi including Candida albicans, Aspergillus ochraceus and Aspergillus fumigetus. All tested crude extracts showed different levels of inhibition activity on bacteria and pathogenic fungi with MIC values varying from 3.13 to 12.5 mg/mL for bacteria and 0.39 to 6.5 mg/mL for pathogenic fungi. These figures show that pathogenic fungi are more sensitive to crude extracts than bacteria, which appear in general more resistant with higher MIC values. Based on these promising results, more refined studies could be envisaged to isolate and determine with accuracy compounds of the crude extracts that are active against bacteria and fungi and thereafter carried out clinical studies on some infectious diseases caused by these bacteria as well as fungal infections including Candidiasis caused by Candida albicans or Aspergillosis caused by Aspergillus fumigetus or Aspergillus ochraceus, the final aim being to develop more efficient medicines based on natural substances against these diseases.