A five year surveillance report on PFGE types of Listeria monocytogenes isolated in Italy from food and food related environments

Listeria monocytogenes can cause severe invasive disease in humans and has been isolated from a variety of foods. This study aimed to investigate type diversity and distribution across sources by subtyping via PFGE a set of 300 L. monocytogenes isolates collected in Italy from foods over a five year period (from 2003 to 2007).The most frequent serotypes were 1/2a (45%), 1/2c (22%), and 4b/4e (16%); 5% of the isolates were untypeable by conventional serotyping. Significant associations were observed between serotype 1/2a with dairy (O.R. = 13.9) and 1/2c with meat (O.R. = 33.3). All isolates were typeable, generating 164 combined PFGE profiles. Of these, 121 were unique, being displayed by only one isolate. The other 43 profiles grouped the remaining isolates and were shared between two (N = 22), three (N = 10), four (N = 3) and five isolates (N = 4). The remaining 4 profiles were shared between 7, 14, 17 and 46 isolates, respectively. Some profiles (N = 7) were retrieved in samples collected in different years, indicating persistency in foods and processing plants. This research may pose the ground for designing a broad typing database which could ease the understanding of L. monocytogenes diversity and could be used for facilitating epidemiological investigations for the identification of listeriosis outbreaks. Data show how large subtype databases may facilitate the identification of common and source-specific types. More comprehensive databases may be needed to fully understand L. monocytogenes diversity and to provide useful data to be considered in epidemiological investigations.