## 3 Results
### Antibacterial Activities of Mushroom Extracts against Wild-Type Bacteria  
Seventy macromycetes extracts (35 EtOAc extracts and 35 MeOH extracts) were evaluated for their antibacterial potential against three Gram-positive bacteria: _Enterococcus faecalis_, _Staphylococcus aureus_, _Staphylococcus epidermidis_, and against two Gram-negative bacteria: _Escherichia coli_ and _Pseudomonas aeruginosa_. The bacteria _S. aureus_, _E. coli_, and _P. aeruginosa_ have been chosen as they are listed as priority pathogens according to the WHO. Although _E. faecalis_ and _S. epidermidis_ are not included in this list, these species are subject to resistance increasing at a non-negligible rate, and which exhibit resistance phenotypes similar to those listed for priority pathogens by the WHO. Our hypothesis that mushrooms produce antibacterial compounds to adapt to their competitive environment was verified, as all mushroom samples exhibited at least one compound active against one bacteria. On bioautograms, active compounds appeared as pale yellow bands, as MTT was not reduced by living bacteria to a blue-purple derivative. The first global observation is that Gram-positive bacteria were much more susceptible to fungal extracts than Gram-negative bacteria. In addition, _E. faecalis_ was generally more affected than _Staphylococcus_ species. This global observation is illustrated in Figure 1, with the effect of an extract from _Arnillaria cepistips_ var. _pseudobulosa_ against the five reference strains. While at least twelve inhibition bands could be clearly detected against _E. faecalis_, a significant decrease in the number of active compounds was observed on the bioautograms against the other bacteria. Just one antibacterial band with a retention factor (Rf) of 0.75 was present on the bioautogram with _E. coli_, while barely any inhibition band could be clearly distinguished against _P. aeruginosa_. This first example also illustrates the main advantage of TLC bioautography over microdilution assays, as this approach is much more informative regarding the constituents involved in antimicrobial activity. Indeed, diffusion and dilution methods give an idea of the antibacterial potential of an extract, but cannot assess the number nor first clues about the compounds involved in this bioactivity. In addition, TLC bioautography enables us to notice active compounds specific to a fungal species or specific against a bacterial strain. This is also exemplified in Figure 2, which presents bioautograms against the three Gram-positive bacteria obtained for EtOAc extracts from five different mushrooms. We can observe on all bioautograms an inhibition zone at Rf values around 0.78 for each of the five fungal species, indicating the presence of a common low-polarity compound that inhibits the growth of the three tested Gram-positive bacteria. Bioautography also enables us to reveal active compounds specific to a fungal species. This is illustrated with an inhibition band at Rf 0.65 present only in _Scleroderma citrinum_ #2 (lane 3), active against the three bacterial strains. In addition, Figure 2 shows that some compounds are more selective; for example, mushrooms 1 to 4 possess a compound eluting at Rf 0.45 that prevents the growth of _E. faecalis_, but that has no effect on both _Staphylococcus_. Similarly, two compounds from _Fomitopsis pinicola_ (lane 5) eluting at Rf 0.20-0.30 inhibit the growth of _E. faecalis_ and _S. aureus_, but do not affect the development of _S. epidermidis_. The polypore _Fomitopsis pinicola_ also contains more polar compounds (Rf 0-0.15) that inhibit the growth of both _Staphylococcus_ but not the growth of _E. faecalis_. These examples demonstrate the diversity and selectivity of antibacterial compounds present in mushrooms. The overall number of inhibition zones is reported in Table 2, and details of inhibition zones with corresponding retention factors (Rf) values can be found in Tables A3-A7. Figure 1: TLC bioautograms obtained with the EtOAc extract from _Armillaria cepistipes_ var.