Determination of Listeria monocytogenes Growth during Mushroom Production and Distribution

Dara Leong,Floriane Guillas,Avelino Alvarez-Ordóez,Kieran Jordan

doi:10.3390/foods2040544

Dara Leong, Floriane Guillas + Show 2 more

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https://doi.org/10.3390/foods2040544

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Abstract

In the EU, food is considered safe with regard to Listeria monocytogenes if its numbers do not exceed 100 CFU/g throughout the shelf-life of the food. Therefore, it is important to determine if a food supports growth of L. monocytogenes. Challenge studies to determine the ability of a food to support growth of L. monocytogenes are essential as predictive modelling often overestimates the growth ability of L. monocytogenes. The aim of this study was to determine if growth of L. monocytogenes was supported during the production and distribution of mushrooms. A three-strain mixture of L. monocytogenes was inoculated onto three independent batches of whole mushrooms, sliced mushrooms, mushroom casing and mushroom substrate at a concentration of about 100–1000 CFU/g. The batches were incubated at potential abuse temperatures, as a worst case scenario, and at intervals during storage L. monocytogenes numbers, % moisture and pH were determined. The results showed that the sliced and whole mushrooms had the ability to support growth, while mushroom casing allowed survival but did not support growth. Mushroom substrate showed a rich background microflora that grew on Listeria selective media and this hindered enumeration of L. monocytogenes. In the case of this study, Combase predictions were not always accurate, indicating that challenge studies may be a necessary part of growth determination of L. monocytogenes.

Highlights

The incidence of Listeria monocytogenes infection is relatively low, listeriosis has the third highest mortality rate of all foodborne pathogens
Mushroom substrate was found to have a rich background non-Listeria microflora which possessed the ability to grow on Listeria chromogenic agar plates
Regarding mushroom casing challenge tests, L. monocytogenes numbers increased by approximately 1 log unit over the first 50 h of incubation at 20 °C (Figure 1)

Summary

Introduction

The incidence of Listeria monocytogenes infection is relatively low, listeriosis has the third highest mortality rate of all foodborne pathogens. Listeriosis outbreaks have commonly been linked to dairy, egg, meat and fish products and produce in the past [3,4]. L. monocytogenes is widespread in the environment so it is not surprising that it is occasionally found in food. Predictive modelling based on experiments performed with laboratory media can be used to give an estimate of the ability of a food to support growth of L. monocytogenes, but in many cases, growth is predicted where there is no growth [7,8,9]. Challenge studies to determine the ability of a food to support growth of

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