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Chapter 18 : Listeria monocytogenes in Milk, Cheese, and the Dairy Environment
Category: Applied and Industrial Microbiology; Food Microbiology
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The realization that listeriosis was a foodborne disease was largely due to the involvement of Listeria monocytogenes-contaminated dairy products in the earliest recognized foodborne outbreaks. Thus, dairy sample matrices are routinely included in developing and validating rapid methods for L. monocytogenes in all food categories. Dairy samples represent a full range of physical characteristics from fluid (milk) through semisolid (yogurt) to soft solid (butter, cream, some cheeses) and hard solid (other cheeses). Environmental sampling can be relatively simple physically but can possibly be complicated by the degree of attachment to surfaces and sequestration in biofilm matrices. Sampling of the production and processing environment can be a useful tool to identify and prevent the presence of L. monocytogenes in dairy products and also for validating and verifying the correct functioning of their procedures based on hazard analysis and critical control point (HACCP) principles and good hygiene practice. A proper sample preparation is critical for rapid methods of listeria detection and enumeration. This chapter presents guidelines for the various general types of dairy samples. Rapid methods for detection of L. monocytogenes can be interpreted as a reduction in the number of days to obtain a result, but the process may still take a relatively long time, i.e., days rather than hours. These rapid methods include (i) agar-based methods including chromogenic agars, (ii) immunoassay-based methods, (iii) concentration methods, and (iv) molecular methods.
Alternative modes of complementation of standard cultural detection methods with rapid methods.
Sampling plans for Listeria monocytogenes applied in Europe (EC 2073/2005) a
Real-time PCR MPN enumeration of viable L. monocytogenes scheme a
Enumeration scheme for environmental Listeria a