Edited by: Steve J. Charette, Université Laval, Canada
Reviewed by: Christian U. Riedel, University of Ulm, Germany; Efstathios D. Giaouris, University of the Aegean, Greece
*Correspondence: Kieran Jordan, Food Safety Department, Teagasc Food Research Centre, Moorepark, Fermoy, Co. Cork, Ireland e-mail:
This article was submitted to Microbial Physiology and Metabolism, a section of the journal Frontiers in Microbiology.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Although rates of listeriosis are low in comparison to other foodborne pathogenic illness, listeriosis poses a significant risk to human health as the invasive form can have a mortality rate as high as 30%. Food processors, especially those who produce ready-to-eat (RTE) products, need to be vigilant against
Mild listeriosis, an infection of the gastrointestinal tract by
Food processors need to be vigilant against
Ready-to-eat (RTE) foods are in a higher risk category than other foods as the heat step of cooking, which would kill any
The aim of this study was to monitor the occurrence and persistence of
From March 2013 to March 2014, a total of 48 food processing facilities from various food sectors, i.e., dairy (18 facilities), meat (12 facilities), seafood (8 facilities), fresh-cut vegetable (6 facilities), miscellaneous (4 facilities), were analyzed bimonthly for the presence of
Food business operators (FBOs) received detailed instructions which included information on how to take swab samples, which areas to sample, the type of food samples required and on the packaging and shipment of the samples to the laboratory. For swab samples, all FBOs were asked to take samples from three specific areas: a drain in the main processing hall, an area of floor (1 m2) and a storage shelf. Because of the variation in layout of the facilities, the area to swab for the remaining samples was freely chosen by the FBO from anywhere in the food processing environment, although cutting areas, brine (if relevant), walls, other drains and pooled water were suggested as optimum locations. For food samples, FBOs were instructed to send two food samples which were at the stage of being ready to be sent from the processing facility.
Every second month, FBOs took 6 environment samples and sent them to the laboratory at Moorepark by overnight courier along with 2 food samples. Thirty-seven FBOs were initially enrolled in the monitoring programme and 11 further FBOs later showed their interest in joining the collaborative network at different stages during the sampling year. On the other hand, 3 FBOs no longer wished to take part in the analysis or went out of business and several other companies missed one or various sample submissions throughout the year's sampling.
Samples were analyzed for the presence of
After incubation, ALOA agar plates were examined for typical
All stocked isolates were confirmed as
PFGE analysis was performed with the restriction enzymes
Overall, 2006 samples were analyzed for the presence of
In the total samples, slight variability in
Thirty out of the 48 processing facilities analyzed had at least one positive sample over the course of the study. However, the majority of processing facilities consistently had a low prevalence of
Variability in
When a food or environmental sample was found positive for
PFGE analysis of
PFGE analysis also allowed the identification of transfer of
A few persistent pulsotypes were found in more than one food business (Figure
Several other pulsotypes were isolated from more than one facility but were only found at one time point and, as such, have not yet been shown to be persistent.
Two thousand and six samples were submitted for analysis. Only 20 FBOs submitted all scheduled samples, therefore the number of samples submitted was less than originally planned. This was not detrimental to the study as a large number of samples were analyzed, allowing the examination of general
While both the dairy and meat sectors showed an average prevalence of 3.9 and 4.2%, respectively, previous studies have found a much higher prevalence in seafood samples (Garrido et al.,
On the other hand, the food sector with the highest occurrence of
Regarding the miscellaneous sector, although a high occurrence of 7.1% was observed, only one of the four facilities (facility 46) tested positive for
For 37.5% of the facilities tested,
Differences in
From the present study, the importance of analyzing isolates from both the 1st and 2nd enrichment can be seen. In only 48.9% of positive samples, both the 1st and 2nd enrichments were positive while in 51.1% of positive samples, either the 1st or the 2nd enrichment only was positive. In some studies, only the 2nd enrichment is plated for
The ratio of serotypes found in the present study was in agreement with a 5 year surveillance report on similar food and food processing environment samples conducted in Italy in 2010 (Nucera et al.,
Several strains of
Several pulsotypes were also seen to be common to several different facilities. There is no known epidemiological link between any of the facilities which shared
The prevalence of
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The authors wish to acknowledge the co-operation of all food business operators involved in this work. Additional thanks to the Veterinary Food Safety Laboratory, Cork County Council. This work was supported by the Irish Department of Agriculture and Food and the Marine under the Food Institutional Research Measure (FIRM) project number 11F008.