Detection of Listeria monocytogenes in raw and pasteurized liquid whole eggs and characterization by PFGE Katell Rivoal a, ⁎, Stéphane Quéguiner a , Evelyne Boscher a , Stéphanie Bougeard a , Gwennola Ermel b , Gilles Salvat a , Michel Federighi c , Florence Jugiau c , Jocelyne Protais a a AFSSA, French Food Safety Agency, BP 53, F-22 440 Ploufragan, France b UMR CNRS 6026-University of Rennes 1, Faculty of Sciences, Beaulieu campus, CS74205, F-35042 Rennes, France c UMR-INRA 1014, ENVN, B.P. 40706, 44307 Nantes Cedex 3, France abstract article info Article history: Received 24 July 2009 Received in revised form 4 January 2010 Accepted 10 January 2010 Keywords: Listeria monocytogenes Egg products PFGE Listeria monocytogenes has been recognized as a human pathogen for decades and is known to be an important foodborne pathogen. There have been no documented foodborne L. monocytogenes illnesses due to the consumption of eggs or egg products, even though the bacterium has been isolated from faeces, body fluid, and oviducts of asymptomatic laying hens. In order to describe L. monocytogenes contamination of egg products, 144 liquid whole egg samples were collected from 3 different egg-breaking plants during 3 sampling periods. L. monocytogenes detection was performed on raw samples stored at 2 °C for two days (D + 2) and on pasteurized samples stored at 2 °C at D + 2 and at shelf-life date (SLD). L. monocytogenes was detected in 25 of the 144 raw egg samples collected, in 4 of the 144 pasteurized egg samples at D + 2 and in 2 of the 144 ones analysed at SLD. Contamination of raw egg products appeared to be season dependant and was higher during summer and winter than during autumn. One hundred and ninety-six L. monocytogenes isolates were collected and serotyped; 3 serovars were demonstrated. The dominant serovar was L. monocytogenes 1/2a which was presented by 94.4% of the isolates. Typing of 196 L. monocytogenes isolates was carried out by macrorestriction of the genomic DNA with ApaI and AscI enzymes followed by pulsed field gel electrophoresis (PFGE). A large diversity was observed with 21 genotypes of L. monocytogenes, even for a given manufacturer. Nevertheless, most of the egg product samples were contaminated by one genotype, except for five samples which were contaminated by two or three distinct genotypes. The genotypes seem to be specific to each manufacturer. No cluster of L. monocytogenes was found to recur in the different plants over successive seasons. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Human listeriosis, caused by Listeria monocytogenes, is a serious bacterial infection, which leads to meningitis or meningo-encephalitis, bacteriaemia and septicaemia and is highly lethal. Between 1991 and 2002, in Europe, a total of 19 outbreaks of invasive listeriosis were reported in nine different countries, with a total of 526 outbreak related cases (De Valk et al., 2005). The implementation of mandatory reporting in France since 1998 has improved the system for moni- toring human listeriosis by requiring additional investigations to identify the sources of foodborne listeriosis (Goulet et al., 2001). Different epidemiology studies undertaken over the last 20 years have demonstrated that most of the human cases of listeriosis were foodborne (Schlech et al., 1983). The foodstuffs that are generally found to be involved are milk and milk products, meat and meat products, plant products and fish and fish products. Eggs and egg products have never been incriminated despite the fact that L. mono- cytogenes has been isolated on eggshells and in the environment of laying hens. Chemaly et al. (2008) found it in 31 out of 200 laying hen farms (15.5%) in dust and faeces samples. The bacterium also appears to be fairly resistant under storage and handling conditions of shell eggs (Brackett and Beuchat, 1992). It can survive shell egg washing procedures and can be isolated from the water used for such washing (Laird et al., 1991; Jones et al., 2006). Listeria spp. has been found very rarely in egg products within egg-breaking plants (Leasor and Foegeding, 1989; Moore and Madden, 1993; Ohkochi et al., 2009). All these references suggest that Listeria may be present on egg shells. Besides, even though there has been no research done on the bacterium in an egg-breaking plant environment, its presence appears inevitable regarding the data published by Gudbjörnsdottir et al. (2004) who have isolated Listeria very frequently in the environment International Journal of Food Microbiology 138 (2010) 56–62 ⁎ Corresponding author. Hygiene & Quality of Poultry and Pig Products, French Food Safety Agency, BP 53, F-22 440, Ploufragan, France. Tel.: + 33 2 96 01 62 22; fax: +33 2 96 01 62 23. E-mail address: k.rivoal@ploufragan.afssa.fr (K. Rivoal). 0168-1605/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ijfoodmicro.2010.01.013 Contents lists available at ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro