Sphagnum peat-based casing soils do not permit the survival of Listeria monocytogenes & Salmonella sp

Mushroom News, Sept, 2006 by Naveen Chikthimmah, Robert Beelman, Luke LaBorde

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CONCLUSIONS

Peat-based mushroom casing soils that were not heat-treated did not support the survival or growth of L. monocytogenes or Salmonella sp. Rather, the pathogens were rapidly destroyed in casing soil. The survival of the foodborne pathogens in casing soil with no native microflora for extended periods emphasizes the importance of a viable and robust casing soil microflora for food safety.

In the need to implement pre-harvest food safety systems, regulatory agencies and buyers may compel growers to implement food safety control measures for casing soils. Fumigation or pasteurization of sphagnum peat-based casing soils may come across as viable alternatives. However, results of this study indicate that these unit operations may negatively affect the native microflora, thereby jeopardizing microbial food safety. Alternatively, growers and researchers should work toward identifying cultural and growing practices that do not negatively affect the native microflora of the casing soil.

The current research was conducted with casing soil that was not colonized with Agaricus mycelia. Studies on the survival of the foodborne pathogens in the presence of Agaricus mycelia and identifying cultural practices that promote a healthy and robust casing microflora throughout the mushroom growing process are two recommended research topics for the future.

Editor's Note: To date, research has not been included for black peats. It is unknown what effects black peat may or may not have on the survival of potential human pathogenic bacteria in casing soils.

REFERENCES

Chikthimmah, N., and R. B. Beelman. 2005. Microbial spoilage of fresh mushrooms. Book chapter in "Microbiology of Fruits and Vegetables." Sapers, G.M., Gorny, J.R., and Yousef, A.E. (eds.). CRC Press. Pp. 135-158.

Kalberer, P. P. 1985. Influence of the depth of the casing layer on the water extraction from casing soil and substrate by the sporophores, on the yield and on the dry matter content of the fruit bodies of the first three flushes of the cultivated mushroom Agaricus bisporus. Sci. Hort., 27:33-43.

Kalberer, P. P. 1987. Water potentials of casing and substrate and osmotic potentials of fruit bodies of Agaricus bisporus. Sci. Hort., 32:175-182.

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Weil, J. 2004. The effect of phase II pasteurization on populations of select human pathogenic bacteria in mushroom compost. M. S. Thesis, The Pennsylvania State University, University Park, PA, University Park, PA.

Wuest, P. J., and G. D. Bengston (ed.). 1982. Penn State Handbook for Commercial Mushroom Growers. Penn State University, University Park, PA, USA.