Anti-Microbial Properties: Anti-microbial effects of a large number of mushroom varieties and mushroom components on both gram-positive and gram-negative bacteria have been confirmed via in vitro studies. A small number of studies in animals have been undertaken and suggest that the antimicrobial effects in vivo may be mediated via the immune system.
Animal model (mouse) studies
Anti-bacterial effects of Agaricus blazei Murill (AbM) have been demonstrated with the AbM extract being protective against systemic Streptococcus pneumoniae 6B infection in mice. The extract was most effective when given 24h before inoculation but it also had protective effects when given together with challenge compared with control. The lack of an antibiotic effect on pneumococci in vitro and increased levels of cytokines MIP-2 and TNF in
the serum of mice receiving AbM extract, indicated that the protective effect of AbM was due to the involvement of the native immune system. The anti-infection properties of AbM have been shown in vivo and the results suggest that AbM extract may be useful as an additional prophylactic and possibly therapeutic treatment against bacterial infections in humans (Bernardshaw et al., 2005a, Bernardshaw et al., 2005b).
A subsequent study by the same group has shown that an extract of Agaricus blazei Murill can protect against lethal septicemia in a mouse model of faecal peritonitis. Bacterial septicemia can occur during gastroenterological surgery. The putatively anti-infective immunomodulatory action of Agaricus blazei Murill (AbM) has been studied in an experimental peritonitis model in BALB/c mice. The mice were orally given an extract of AbM or phosphate-buffered saline 1 day before the induction of peritonitis with various concentrations of faeces from the mice. The state of septicemia, as measured by the number of colony-forming units of bacteria in blood, and the survival rate of the animals were compared between the groups. Mice that were orally treated with Agaricus blazei Murill extract before bacterial challenge showed significantly lower levels of septicemia and improved survival rates (Bernardshaw et al., 2006).
In vitro studies
Agaricus bisporus and Pleurotus sajor caju have been assayed in vitro for their anti-microbial activities using aqueous and organic solvent extracts. It has been shown that Escherichia coli 390, Escherichia coli 739, Enterobacter aerogenes, Pseudomonas aeruginosa and Klebsiella pneumoniae were most sensitive to aqueous, ethanol, methanol and xylene extracts of these mushrooms (Tambekar et al., 2006). Ethanol extracts of Agaricus bisporus have also been shown to have antibacterial activity against both gram positive and gram negative bacteria, as well as anticandidal activity against Candida albicans(Jagadish et al., 2009).
Extracts from fermentation broth and mycelium of 15 strains of Lentinus edodes have been shown to be active against gram-positive and gram-negative bacteria, yeasts and mycelial fungi, including dermatophytes and phytopathogens. The strains differed by the set of the organisms susceptible to the action of the extracts. Strains of L. edodes combining marked anti-bacterial properties and high yields of water soluble polysaccharides were screened. The active compounds were detected by preparative thin layer chromatography. Two were identified with UV and mass spectrometry as lentinamycin B and erytadenine (lentinacin). Lentinamycin B was found to be the main component responsible for the anti-bacterial activity of the L. edodes strains (Soboleva et al., 2006).
The anti-microbial activity of the culture fluid of Lentinus edodes mycelium grown in submerged liquid culture has been demonstrated against Streptococcus pyogenes, Staphylococcus aureus and Bacillus megaterium. The substance responsible for the activity was heat-stable and was suggested to be lenthionine, an anti-bacterial and anti-fungal sulphur-containing compound (Hatvani, 2001).
Three anti-bacterial compounds extracted by chloroform, ethylacetate or water from dried Shiitake mushrooms (Lentinus edodes) have been reported to possess efficient anti-bacterial activities against Streptococcus spp., Actinomyces spp., Lactobacillus spp., Prevotella spp., and Porphyromonas spp. of oral origin. In contrast, other general bacteria, such as Enterococcus spp., Staphylococcus spp., Escherichia spp., Bacillus spp., and Candida spp. were relatively resistant to these compounds. The anti-bacterial activity of chloroform extracts and ethylacetate extracts were relatively heat-stable, while the water extract was heat-labile (Hirasawa et al., 1999).
The action of the juice of Shiitake mushrooms (L. edodes) at a concentration of 5% from the volume of the nutrient medium was found to produce a pronounced anti-microbial effect with respect to Escherichia coli O-114, Staphylococcus aureus, Enterococcus faecalis, Candida albicans and to stimulate the growth of E. coli M-17. Bifidobacteria and lactobacteria exhibited resistance to the action of L. edodes juice (Kuznetsov et al., 2005).
Two cuparene-type sesquiterpenes, enokipodins C (1) and D (2), have been isolated from culture medium of Flammulina velutipes (Enoki), along with enokipodins A (3) and B (4). All the metabolites showed anti-microbial activity against the fungus Cladosporium herbarum, and gram-positive bacteria, Bacillus subtilis and Staphylococcus aureus(Ishikawa et al., 2001).
Anti-bacterial components of the mushroom Podaxis pistillaris have recently been reported. Podaxis pistillaris (Podaxales, Podaxaceae, Basidiomycetes) was found to exhibit anti-bacterial activity against Staphylococcus aureus, Micrococcus flavus, Bacillus subtilis, Proteus mirabilis, Serratia marcescens and Escherichia coli. In a culture medium of P. pistillaris, three epidithiodiketopiperazines were identified by activity-guided isolation. Based on spectral data their identity was establishedas epicorazine A(1), epicorazine B(2) and epicorazine C (3, antibiotic F 3822), which have not previously been reported as constituents of P. pistillaris(Al-Fatimi et al., 2006).
Aqueous extracts of Shiitake and Oyster mushrooms have been tested qualitatively against a panel of 29 bacterial and 10 fungal pathogens. Shiitake mushroom extract had extensive antimicrobial activity against 85% of the organisms tested, including 50% of the yeast and mould species in the trial. This compared favourably with the results from both the positive control (Ciprofloxacin) and Oyster mushroom, in terms of the number of species inhibited by the activity of the metabolite(s) inherent to the Shiitake mushroom (Hearst et al., 2009).
A polysaccharide-rich fraction of Agaricus brasiliensis has been evaluated for candidacidal activity, H2O2 and nitric oxide (NO) production, and expression of mannose receptors by murine peritoneal macrophages. The treatment increased fungicidal activity and it was associated with higher levels of H2O2, whereas NO production was not affected. The treatment enhancedmannose receptor expression by peritoneal macrophages. The results suggested that this extract can increase host resistance against some infectious agents through stimulating the microbicidal activity of macrophages (Martins et al., 2008).
The anti-microbial activity of aqueous, methanol, hexane, and ethyl acetate extracts from edible wild and cultivated mushrooms against nine foodborne pathogenic bacterial strains (Escherichia coli O157:H7, Salmonella Enteritidis, Shigella sonnei, Vibrio parahaemolyticus, Yersinia enterocolitica, Bacillus cereus, Clostridium perfringens, Listeria monocytogenes, and Staphylococcus aureus) have been screened. Twenty-nine of the 48 species tested had antimicrobial activity. Methanol, ethyl acetate, and aqueous extracts accounted for 92.8% of the positive assays, whereas the hexane extracts accounted for only 7.2%. Gram-positive bacteria were more sensitive than Gram-negative bacteria to fungal extracts, and C. perfringens was the most sensitive microorganism. Aqueous extracts from Clitocybe geotropa and Lentinula edodes had the highest anti-microbial activity against the bacterial strains tested (Venturini et al., 2008).