Association between phylogeny, virulence potential and serovars of Salmonella enterica.

Salmonella enterica subsp. enterica is one of the leading causes of zoonotic food-borne disease worldwide. The consequence of these infections is a serious impact on economics of the society in the form of lost productivity and expenses for medical care. The objective of this study was to analyze the difference in genomic content between selected serovars, especially the content of pathogenicity genes and this was done with a DNA microarray. Furthermore, we investigated the phylogenetic relationship between serovars using multilocus sequence typing (MLST). We chose serovars Typhimurium and Enteritidis as they are responsible for 75% of human infections in Europe. Additionally, we included serovars Derby, Dublin, Saintpaul, 4,5,12:i:-, Java and 4,5,12:b:- which are suspected to have different degrees of virulence to humans. MLST analysis clustered strains according to serovar with the exception of Java and Derby. DNA microarray clustered strains according to serovar and serogroup except for serovar 4,5,12:b:-. Differences in content of pathogenicity related genes between serovars with various host preferences and virulence towards humans were not observed. However, our strains from the supposedly less virulent serovar Derby lacked a combination of genes important for virulence. It might be speculated that other serovars can sustain their pathogenicity lacking one or two of these genes, whereas lack of many virulence genes will result in reduced virulence. A partial lack of concordance between MLST and microarray was found and this can be explained by the underlying data. On one hand, microarray data include highly variable regions which are known to be involved in horizontal gene transfer. On the other hand, MLST data is restricted to seven sequences and disregards contribution of horizontally acquired genes when evaluating evolution. The DNA microarray and MLST analysis complement each other giving a clearer image of evolution of these serovars and, furthermore, a visualization of the horizontally acquired genes.

Litrup E ，Torpdahl M ，Malorny B ，Huehn S ，Christensen H ，Nielsen EM ... -  《-》

Virulotyping and antimicrobial resistance typing of Salmonella enterica serovars relevant to human health in Europe.

Huehn S ，La Ragione RM ，Anjum M ，Saunders M ，Woodward MJ ，Bunge C ，Helmuth R ，Hauser E ，Guerra B ，Beutlich J ，Brisabois A ，Peters T ，Svensson L ，Madajczak G ，Litrup E ，Imre A ，Herrera-Leon S ，Mevius D ，Newell DG ，Malorny B ... -  《-》

MLST-v, multilocus sequence typing based on virulence genes, for molecular typing of Salmonella enterica subsp. enterica serovars.

Tankouo-Sandjong B ，Sessitsch A ，Liebana E ，Kornschober C ，Allerberger F ，Hächler H ，Bodrossy L ... -  《JOURNAL OF MICROBIOLOGICAL METHODS》

Transposition of the heat-stable toxin astA gene into a gifsy-2-related prophage of Salmonella enterica serovar Abortusovis.

The horizontal transfer and acquisition of virulence genes via mobile genetic elements have been a major driving force in the evolution of Salmonella pathogenicity. Serovars of Salmonella enterica carry variable assortments of phage-encoded virulence genes, suggesting that temperate phages play a pivotal role in this process. Epidemic isolates of S. enterica serovar Typhimurium are consistently lysogenic for two lambdoid phages, Gifsy-1 and Gifsy-2, carrying known virulence genes. Other serovars of S. enterica, including serovars Dublin, Gallinarum, Enteritidis, and Hadar, carry distinct prophages with similarity to the Gifsy phages. In this study, we analyzed Gifsy-related loci from S. enterica serovar Abortusovis, a pathogen associated exclusively with ovine infection. A cryptic prophage, closely related to serovar Typhimurium phage Gifsy-2, was identified. This element, named Gifsy-2AO, was shown to contribute to serovar Abortusovis systemic infection in lambs. Sequence analysis of the prophage b region showed a large deletion which covers genes encoding phage tail fiber proteins and putative virulence factors, including type III secreted effector protein SseI (GtgB, SrfH). This deletion was identified in most of the serovar Abortusovis isolates tested and might be dependent on the replicative transposition of an adjacent insertion sequence, IS1414, previously identified in pathogenic Escherichia coli strains. IS1414 encodes heat-stable toxin EAST1 (astA) and showed multiple genomic copies in isolates of serovar Abortusovis. To our knowledge, this is the first evidence of intergeneric transfer of virulence genes via insertion sequence elements in Salmonella. The acquisition of IS1414 (EAST1) and its frequent transposition within the chromosome might improve the fitness of serovar Abortusovis within its narrow ecological niche.

Bacciu D ，Falchi G ，Spazziani A ，Bossi L ，Marogna G ，Leori GS ，Rubino S ，Uzzau S ... -  《-》

Diversity of Salmonella enterica serovar Derby isolated from pig, pork and humans in Germany.

Salmonella enterica serovar Derby (S. Derby) is one of the most prevalent serovars in pigs in Europe and in the U.S. and ranks among the 10 most frequently isolated serovars in humans. Therefore, a set of 82 epidemiologically unrelated S. Derby strains isolated between 2006 and 2008 from pigs, pork and humans in Germany was selected and investigated in respect to the transmission of clonal groups of the serovar along the food chain. Various phenotypic and genotypic methods were applied and the pathogenicity and resistance gene repertoire was determined. Phenotypically 72% of the strains were susceptible to all 17 antimicrobials tested while the others were monoresistant to tetracycline or multi-resistant with different resistance profiles. Four major clonal groups were identified based on PFGE, sequence data of the virulence genes sopA, sopB and sopD, VNTR-locus STTR5 and MLST revealing also the new sequence type ST774. Thirty different PFGE profiles were detected resulting in four clusters representing the four groups. The pathogenicity gene repertoire of 32 representative S. Derby strains analyzed by microarray showed six types with differences in the Salmonella pathogenicity islands, pathogenicity genes on smaller islets or prophages and fimbriae coding genes. The pathogenicity gene repertoire of the predominant types PAT DE1 and DE2 were most similar to the ones of S. Paratyphi B (dT+, O5-) and to a minor degree to S. Infantis and S. Virchow PATs. Overall this study showed that in Germany currently one major S. Derby clone is frequently isolated from pigs and humans. Contaminated pork was identified as one vehicle and consequently is a risk for human health. To prevent this serovar from entering the food chain, control measurements should be applied at the farm level.

Hauser E ，Hebner F ，Tietze E ，Helmuth R ，Junker E ，Prager R ，Schroeter A ，Rabsch W ，Fruth A ，Malorny B ... -  《-》