Listeriosis is a food borne disease caused by the bacterium L. monocytogenes. In otherwise healthy individuals, listeriosis is usually asymptomatic or may results in mild flu-like symptoms or gastrointestinal illness. However, infection with L. monocytogenes in pregnant women, neonates and immuno-compromised adults can result in a severe and life threatening invasive form of listeriosis. In Europe, after a decline in the number of cases during the 1990s, the incidence of listeriosis increased and has remained relatively high for the past ten years. This has led to listeriosis being considered one of the resurgent foodborne diseases in Europe [1, 2]. This disease is rare but associated with a high fatality rate (20-30%) and currently remains an important public health concern.
Based on its genetic content, L. monocytogenes can be separated into 3 lineages I, II and III. Although 13 serotypes have been described, 98% of strains causing human infections and isolated from foods are of serotypes 4b, 1/2b (Lineage I), 1/2a, and 1/2c (lineages II) . Molecular methods have been developed to assist in the characterization of L. monocytogenes. Doumith et al. (2004)  have described a multiplex PCR assay which cluster L. monocytogenes of lineages I and II into four serogroups: IVb (4b, 4d, 4e); IIa (1/2a, 3a), IIb (1/2b, 3b, 7) and IIc (1/2c, 3c).
Of several molecular methods currently available, macrorestriction analysis by PFGE is one of the most used methods for the subtyping of L. monocytogenes[5, 6]. The combination of restriction endonucleases AscI and ApaI, as advised by PulseNet USA, has shown excellent discrimination for L. monocytogenes and the technique is shown to be reproducible. PFGE, using these two enzymes, is considered to be the international standard for subtyping .
AFLP is a method which combines the digestion of the entire bacterial genome by one or more restriction enzymes, with PCR being used to amplify and detect the digested fragments. Fluorescent AFLP is a variant using fluorescent PCR primers, enabling the amplified digested fragments to be detected and sized accurately by capillary electrophoresis. Various fAFLP assays have previously been developed for subtyping L. monocytogenes and other Listeria spp isolated from food, animals, food processing environment  and human cases [9, 10]. These assays have been described as reproducible and high resolution genotyping techniques that require less time to perform and to analyze than PFGE. Recently, fAFLP with the enzyme pair HindIII/HhaI was applied to L. monocytogenes isolates from foods and the environment , using adaptors and primers previously designed  for typing Campylobacter isolates. This enzyme pair was found to be more suitable for L. monocytogenes than the BamH1/EcoRI pairs . To our knowledge, these authors have compared, for the first time, fAFLP with PFGE combined with the two enzymes ApaI/AscI and demonstrated that the discrimination index (DI) of fAFLP was at least equal to PFGE. However, the strain panel only included field strains isolated from food and food processing environments and not human clinical isolates.
ANSES’s Laboratory for Food safety has been the EURL for L. monocytogenes in the food chain since 2006. ApaI/AscI-PFGE is routinely used at the EURL for the surveillance of food, animals and environmental isolates at the national and European level [14, 15]. One of the main EURL activities is to develop or/and evaluate and keep up to date with new molecular subtyping methods and deploy them through the European NRL network. PFGE is widely acknowledged to be a time-consuming and labor-intensive method: the analyses are completed in 30 hours to three days from receipt of pure culture. It also requires highly skilled operators and does not offer commercially available standardized reagents. To consider a subtyping technique for L. monocytogenes as an alternative to PFGE, one of the first step is to test a panel of strains isolated not only from food and environment samples but also from human cases and to include outbreaks and reference strains .
Since 2008 the UK-NRL for Listeriahas used fAFLP, with the enzyme pairs HindIII/HhaI, as the subtyping method for the routine surveillance of L. monocytogenes isolated from human clinical cases, food and food processing environments in the UK.
The objective of this study was to compare results obtained using fAFLP and PFGE, on a panel of L. monocytogenes isolates from human clinical cases, foods, food processing environments and animals. The panel included isolates known to be associated with outbreaks and sporadic cases of listeriosis, as well as reference strains, 3 of which were fully sequenced. The value of fAFLP for the routine subtyping of L. monocytogenes, in terms of its discriminatory ability and usefulness in detecting and investigating clusters of listeriosis cases for the NRLs, will be discussed.