Identification and Molecular Characterization of Bacteria and Fungi Associated with Three Fresh Edible Mushrooms

Abstract

Aims: Mushrooms are health-food used as food supplements and fortification but are susceptible to microbial spoilage due to high moisture content and nutrient status. Fresh mushrooms sometimes show signs of spoilage after harvest and makes storage difficult. The objective of the study was to identify and characterize bacteria and fungi associated with three fresh edible mushrooms, under ambient and cold temperatures.
 Methodology: The study was conducted at the Bells University of Technology, Nigeria, between December 2020 and October 2021. Pleurotus ostreatus and Calocybe indica fruitbodies were procured from the Federal Institute of Industrial Research Oshodi while Pleurotus tuber-regium fruitbodies were obtained from sclerotia planted in loamy soil. The fruitbodies were kept at ambient (28oC) and cold (15oC) temperatures respectively. The bacterial and fungal counts on each of the mushrooms were taken at 0,3, 5, and 7 days after harvest. The isolated bacteria were identified by conventional methods; Analytical Profile Index (API) 20E kits (BioMerieux), while Fungi were identified by morphological features and PCR amplification using ITS 1f/ ITS 4r universal primers. 
 Results: The bacterial and fungal counts on the fruitbodies ranged from 5.7 log CFU/ml – 6.3 log CFU/ml and 5.0 log CFU/ml – 5.9 log CFU/ml respectively. Seven genera of bacteria isolated were gram-negative bacteria. At ambient temperature, Pseudomonas aeruginosa, Enterobacter asburiae, Klebsiella oxytoca, Klebsiella ornithinolytica, Serratia marcescens, Chryseobacterium meningosepticum and Cedecea davisae were isolated while Enterobacter cloacae, Enterobacter sakazakii and Citrobacter braakii were isolated at cold temperature. Aspergillus, Penicillium, and Fusarium were isolated at both temperatures while Alternaria was isolated at ambient temperature.
 Conclusion: Isolated bacteria and fungi were mostly enteric pathogens and potential mycotoxin-producing fungi. This is an indication that strict hygiene and control measures should be put in place during the production and storage of these mushrooms in order to improve the quality and food safety of fresh mushrooms in Nigeria.