Evaluation of microbial safety and cross-contamination sources in button mushroom (Agaricus bisporus) production

Abstract

This study aimed to investigate the contamination sources of button mushrooms by assessing the microbial load on the mushrooms and in the agricultural inputs that come into contact with the mushroom. A total of 234 samples including mushrooms, compost, casing soil, and tools from A, B, C, and D farms were tested for sanitary indicators (aerobic bacteria, coliforms, and Escherichia coli) and foodborne pathogens (E. coli O157:H7, Salmonella spp., Staphylococcus aureus, and Listeria monocytogenes). To identify the contamination source, E. coli was isolated and analyzed using MLST (Multi-Locus Sequence Typing). The number of aerobic bacteria remained consistent during composting (⟩7 log CFU/g); however, the occurrence of coliforms and E. coli was reduced to the detection limit (⟨1.0 log). Salmonella spp. and L. monocytogenes were detected in the raw material; however, they were inactivated during composing. More than 6.0 log of aerobic bacteria and 3.0 log of coliforms were observed in the casing soil from A, B, and C farms and in the gloves from the C farm. MLST indicated that the STs of E. coli isolated from casing soil layer and from the harvested mushrooms were identical at ST 189. Therefore, cross contamination occurred through the casing soil layer, and this could contribute to E. coli contamination in mushrooms. It is necessary to practice hygiene guidelines, such as sterilization of casing soil, worker hygiene, and facility sanitation, to minimize the potential of microbial contamination in mushrooms.