Mustafa N. Owaid 1,2 , Sajid Salem S. Al-Saeedi 2 , and Idham Abed Ali Al-Assaffii 3 2 Department of Biology, College of Science, University of Anbar, Ramadi, Anbar 31001, Iraq 3 Department of Soil and Water, College of Agriculture, University of Anbar, Ramadi, Anbar 31001, Iraq Email: mustafa@alheeti.com Abstract— oyster mushrooms: Pleurotus ostreatus (grey and white strains), Pleurotus cornucopiae (bright yellow strain) and Pleurotus salmoneostramineus (pink stain) in form filtrates and mycelia were investigated against five standard strains of pathogenic bacteria and yeast. The filtrate of P. salmoneostramineus was best one compared with other filtrates against Pseudomonas aeruginosa ATCC 27853 and Candida parapsilosis ATCC 22019 respectively. Escherichia coli ATCC 25922, Enterococcus faecalis ATCC 29212 and Staphylococcus aureus HIP10267 have low sensitive. Mycelia of P. cornucopiae inhibited colonies of the bacterium Enterococcus faecalis ATCC 29212 and yeast Candida parapsilosis ATCC 22019 at 5.21% and 29.19% respectively. Escherichia coli ATCC 25922 was sensitive for mycelia of P. salmoneostramineus only in significant (P< 0.05) inhibition value 6.67%. Index Terms—pleurotus spp. antimicrobial activity. culture filtrate. mycelia. interaction. I. INTRODUCTION Oyster mushroom is an edible mushroom, can be cultivated on a wide variety of substrates containing lignin and cellulose. It has nutritional and medicinal properties [1]. Pleurotus spp. belongs to Basidiomycota, order Agaricales, and the family Tricholomataceae. The fungi is important source for some chemicals such enzymes and antibiotic [2]. Consequently, the antimicrobial activity of various polysaccharides from medicinal mushrooms is being re-evaluated in terms of their clinical efficacy. Such compounds would be expected to function by mobilizing the body’s humoral immunity to ward off viral, bacterial, fungal and protozoal infections resistant to current antibiotics [3]. Medicinal mushrooms are able to synthesize a great amount of secondary metabolites that present antitumoral, antiviral and anti-inflammatory activities [4]. Mushrooms have been used as food supplement from times immemorial not only for their flavor, aroma and nutritive Manuscript received July 1, 2014; revised October 25, 2014; values but also for their medicinal properties as evident from ancient literature [5]. Currently, a large range of mushrooms species are grown in liquid medium. The obtained mycelium is used for various applications, such as obtaining dietary supplements, pharmaceutical applications, conversion of waste into biomass and production of enzymes [1]. “[6]” find the secondary metabolism of Pleurotus erngii was active against Bacillus megaterium, Staphylococcus aureus, Escherichia coli, Candida albicans, C. glabrata and Epidermophyton spp. Generally, many studies find different activity of extracts of mushrooms against different pathogenic bacteria [7, 8, 9]. Pleurotus spp. has changeable activity against Gram-negative pathogenic bacteria and strong inhibition against Gram-positive pathogenic bacteria: Bacillus subtilis and Micrococcus luteus [10]. However, this article showed antibacterial and anti-yeast activity of mycelial of four species of oyster mushrooms and their liquid culture filtrate in vitro. II. MATERIAL AND METHODS A. Strains Four oyster mushrooms species: Pleurotus ostreatus (grey), Pleurotus ostreatus (white), Pleurotus cornucopiae var. citrinopileatus (bright yellow) and Pleurotus salmoneostramineus (pink) were obtained from Mushroom Box Company, Monmouth, UK, in form spawn and sub cultured it on Potato Dextrose Agar (PDA) medium at 25 C° for this experiment. Five standard strains of microbes, bacteria: Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus HIP10267 and Enterococcus faecalis ATCC 29212 and yeast: Candida parapsilosis ATCC 22019 obtained from USA. B. Media and Liquid Culture Filtrate Preparation In this experiment, Potato dextrose broth (PDB) and potato dextrose agar (PDA) were prepared [11]. The oyster mushrooms were cultured in Potato Dextrose Broth (PDB) by using five centimeter disk of seven days old culture in flask (250 ml) contains 50 ml of PDB, incubated at 25±1 C° for 20 days with once shake every 376 Journal of Medical and Bioengineering Vol. 4, No. 5, October 2015 ©2015 Engineering and Technology Publishing doi: 10.12720/jomb.4.5.376-380 1 Athar School, Heet Education, Ministry of Education, Hit, Anbar 31007, Iraq Antimicrobial Activity of Mycelia of Oyster Mushroom Species (Pleurotus spp.) and their Liquid Filtrates (In Vitro) , antimicrobial activity of four species of In vitro