Abstract
The aim of the present study was to evaluate the persistence of Listeria monocytogenes in raw milk from vending machines, based on culture and molecular detection of pathogen and Pulsed-Field Gel Electrophoresis typing. From December 2015 to January 2017, a total of 319 milk samples from 36 vending machines were examined for the presence and count of L. monocytogenes by reference methods ISO 11290:1 and ISO 11290:2. Molecular detection of pathogens was performed by loop-mediated isothermal DNA amplification (LAMP) coupled with bioluminescence (Molecular Detection Assay). L. monocytogenes was detected by MDA in 14 milk samples (4.38%) from four farms, compared to eight positive samples (2.5%) retrieved by a reference ISO method. Cultivable L. monocytogenes isolates were subjected to Pulsed-Field Gel Electrophoresis typing and pulsotypes were compared with those obtained during the previous survey in Croatia (2014‒2015). It was found that identical PFGE patterns of L. monocytogenes occur in milk samples of the same producer over a three-year period, indicating the persistence of pathogens in raw milk vending machines. The results obtained support the need for more effective control of milk in the entire food chain.
Highlights
Consumption of raw milk is popular in some European countries (e.g., Italy, the UK), includingCroatia, due to a belief in the health benefits of such milk and the trend for consuming raw or unprocessed foods
The presence of L. monocytogenes was determined by loop-mediated isothermal DNA amplification (LAMP) method coupled with bioluminescence
The incidence of L. monocytogenes in this study is similar to a previous survey of milk vending machines in Croatia (2014–2015), in which four samples (n = 87, 4.59%) were contaminated with the pathogen [4]
Summary
Consumption of raw milk is popular in some European countries (e.g., Italy, the UK), including. Due to a belief in the health benefits of such milk and the trend for consuming raw or unprocessed foods. In Croatia, raw milk may be placed on the market via milk vending machines (81 registered milk vending machines as of April 2019; Veterinary and Food Safety Directorate) and consumed after boiling (recommendations for consumers). Boiling the milk is the only method for ensuring microbiological safety [1,2]; the responsibility is in the hands of the consumers, who often underestimate the risks associated with the consumption of raw milk [3]. Raw milk can be contaminated by different pathogenic bacteria such as Campylobacter, Salmonella, Shiga toxin-producing Escherichia coli (STEC), and Listeria monocytogenes [5]. The presence of L. monocytogenes in unpasteurized milk and cases of human listeriosis due to the consumption of Beverages 2019, 5, 46; doi:10.3390/beverages5030046 www.mdpi.com/journal/beverages
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