Evaluation and bacterial populations associated with fresh mushrooms (agaricus bisporus)

Doores, Stephanie, Kramer, Michael, and Beelman, Robert. 1986. Evaluation of bacterial populations associated with fresh mushrooms (Agaricus bisporus) Proc. Int. Symp. Tech Aspects Cult. Edible Fungi Total aerobic bacterial counts on mushrooms were determined for the first six flushes of the crop cycle and the casing material and water were sampled at selected intervals. Total bacterial numbers ranged from 2. 1 to 16 × 10⁶ CFU/g; numbers were relatively constant through the fifth flush of the crop cycle and decreased slightly by flush 6. Counts from casing material were considerably higher, between 1. 7 and 2. 9 × 10⁸ CFU/g and also were relatively constant over the cycle. Bacterial counts from tap water were lower and did not appear to contribute to overall microbial populations. The majority (54. 0%) of bacteria isolated from the individual flushes were identified as fluorescent pseudomonads with flavobacteria comprising the second largest group (10. 0%). The proportions of these two organisms remained relatively constant; however, the pseudomonads decreased between the fifth and sixth flush while the flavobacteria increased. Bacterial populations during postharvest storage at 13°C increased from an initial load of 10⁷ CFU/g to almost 10¹¹ CFU/g. The same two groups predominated but the proportion of flavobacteria increased during later storage. A third group of pseudomonads having mucoidal colonies appeared during storage in a biphasic manner. Deterioration of mushroom quality as indicated by maturity and color measurement appeared concomitant with bacterial growth indicating that darkening is related to increased bacterial numbers. However, phytopathogenic strains of microorganisms responsible for blotch occurred in very low numbers during storage.