Antibacterial Activity of Spent Substrate of Mushroom Pleurotus ostreatus Enriched with Herbs

The recurrent use of antibiotics has given the guideline so that bacteria will develop resistance to drugs used in medicine, which is why recent investigations have been directed to evaluate natural sources such as plants or fungi, which can fight the bacteria. Here the antibacterial activity of spent substrate of Pleurotus ostreatus combined with medicinal plants was evaluated. We designed six mixtures (barley straw, barley straw/Chenopodium ambrosioides L., barley straw/Mentha piperita L., barley straw/Rosmarinus officinalis L., barley straw/Litsea glaucescens Kunth and barley straw/Tagetes lucid Cav) to be used as a substrate of cultivation of mushroom. These were recovered after the harvest. We obtained aqueous extracts from spent substrates and resuspended them to different concentrations (25, 50 and 100 mg mL-1). These were tested for antibacterial activity against Staphylococcus epidermidis, Bacillus subtilis and Escherichia coli; as a positive control we used azithromycin, cephalexin and dicloxacillin. The protocol was a completely randomized assay with a factorial arrangement design. The data were analyzed with PROC GLM, SAS. The spent substrate from Pleurotus ostreatus that contained Mentha piperita L. presented the largest zone of inhibition against Staphylococcus epidermidis (40.00 mm) which was similar to control antibiotics (40.00 mm). Second in toxicity was the spent substrate from barley straw extract (33.33 mm). In conclusion, the results suggest that it is possible to use the spent substrate of Pleurotus ostreatus as source of extracts with antibacterial activity, being the best option the combination of barley straw with Mentha piperita L.