Characterization of Listeria monocytogenes strains isolated from food and environmental samples

This study aimed to investigate type diversity and distribution over time and across sources by subtyping via Pulsed Field Gel Electrophoresis (PFGE) a set of 300L. monocytogenes strains collected over a five year period. Five clinical human strains isolated in the same geographic area and period of the study were also included in the analysis. The isolated strains belonged to serotype 1/2a (45 % of the samples), 1/2c (22 %), 4b/4e (16 %); however, 5 % of the strains were untypeable. Significant associations were observed between serotype 1/2a with dairy (O.R.= 13.9; χ2 p < 0.05) and 1/2c with meat (O.R.= 33.3; χ2 p < 0.05). PFGE results highlighted 152 pulsotypes shared among two or more samples: 9 pulsotypes were recurrent and 6 were shared between strains isolated from different food and environmental sources. The other generated pulsotypes were source specific and/or retrieved in one year only. These findings may indicate the presence of both nicheadapted as well as ubiquitous PFGE types. Moreover, no PFGE types were shared between strains collected from food/environmental isolates and human clinical strains. The results of this research underline and confirm the importance of implementing a broad typing database which could facilitate epidemiological investigations and enhance novel food attribution modelling approaches for the identification of listeriosis outbreaks and the related sources.These data, even if focused on strains collected in a limited geographic area, may pose the ground to evidence how large subtype databases may aid in the detection of common- and source specific- types. However, more comprehensive databases, both at national and at European level, are needed to revealL. monocytogenes strains diversity and to provide useful data for epidemiological investigations.