One contribution of 16 to a theme issue 'Interoception beyond homeostasis: affect, cognition and mental health'.

This study is a first step in the development of multilocus sequence typing (MLST) method for Listeria monocytogenes. Nine housekeeping genes were analyzed in a set of 62 strains isolated from different sources and geographic locations in Spain. These strains were previously characterized by pulsed-field gel electrophoresis (PFGE). Because of low diversity, two loci were discarded from the study. The sequence analysis of the seven remaining genes showed 29 different allelic combinations, with 22 of them represented by only one strain. The results of this sequence analysis were generally consistent with those of PFGE. Because MLST allows the easy comparison and exchange of results obtained in different laboratories, the future application of this new molecular method could be a useful tool for the listeriosis surveillance systems that will allow the identification and distribution of analysis of L. monocytogenes clones in the environment.Listeria monocytogenes is an opportunistic pathogen widely distributed in the environment. The ubiquity of this microorganism makes especially necessary the use of typing methods for the study of its epidemiology. Numerous molecular methods have been applied to the characterization of L. monocytogenes isolates, e.g., multilocus enzyme electrophoresis (MLEE) (1), pulsed-field gel electrophoresis (PFGE) (2, 29), random amplified polymorphic differences (19), and ribotyping (30), etc. By these methods the species is divided into two genetic divisions which are correlated with the flagellar antigen groups division I, composed of strains of serotypes 1/2a and 1/2c, and division II, which is composed of strains of serotypes 1/2b and 4b. Both divisions are characterized by nonoverlapping allelic variants of different genetic markers, suggesting strong linkage disequilibrium and an apparent lack of gene exchange between them (15). This is consistent with the hypothesis that the genetic structure of L. monocytogenes populations is basically clonal (21). Recently, an additional division has been proposed based on the variability of the sequence of several genes involved in virulence (22).MLEE has been the most widely used molecular method to study the genetic structure and epidemiology of pathogenic bacterial species. Recently, a novel molecular typing method based on the principles of MLEE (25) has been developed, multilocus sequence typing (MLST). This technique was primarily designed and validated for Neisseria meningitidis (17). Afterwards, it was successful in the characterization of several other pathogenic bacteria, such as Streptococcus pneumoniae (5), Streptococcus pyogenes (8), Staphylococcus aureus (7), and Campylobacter jejuni (4).MLST makes use of automated DNA sequencing to characterize the alleles present at different housekeeping genes.Because it is based on nucleotide sequence, it is highly discriminatory and provides unambiguous results that are directly comparable among laboratories via the internet (7). In addition, this method is particularly suited to global epidemiol...