Cultivable microbiome of fresh white button mushrooms

Abstract

Microbial dynamics on commercially grown white button mushrooms is of importance in terms of food safety assurance and quality control. The purpose of this study was to establish the microbial profile of fresh white button mushrooms, with the focus on potential presence of food-borne pathogens. The total microbial load was determined through standard viable counts. Presence and isolation of gram-negative bacteria including coagulase positive Staphylococci were performed using a selective enrichment approach. Dominant and presumptive organisms were confirmed using molecular methods. Total mushroom microbial counts ranged from 5.2 to 12.4 log cfu g-1, with the genus Pseudomonas being most frequently isolated (45.37% of all isolations). In total, 91 different microbial species were isolated and identified using Matrix assisted laser desorption ionisation time of flight mass spectrophotometry, PCR and sequencing. Considering current food safety guidelines in South Africa for ready-to-eat fresh produce, coliform counts exceeded the guidance specifications for fresh fruit and vegetables. Based on our research and similar studies, it is proposed that specifications for microbial loads on fresh, healthy mushrooms reflect a more natural microbiome at the pointof- harvest and point-of-sale.