The emerging enteric pathogen Campylobacter concisus is associated with prolonged diarrhea and inflammatory bowel disease. Previous studies have shown that C. concisus strains are very genetically diverse. Nevertheless, C. concisus strains have been divided into two genomospecies, where GS1 strains have been isolated predominantly from healthy individuals, while the GS2 cluster consists of isolates primarily from diarrheic individuals. The aim of the present study was to determine the genetic diversity of C. concisus isolates from Danish diarrheic patients. Multilocus sequence typing using the loci aspA, atpA, glnA, gltA, glyA, ilvD and pgm, as well as genomospecies based on specific differences in the 23S rRNA, was used to characterize 67 isolates (63 fecal and 4 oral), from 49 patients with different clinical presentations (29 with diarrhea, eight with bloody diarrhea, seven with collagenous colitis and five with Crohn's disease). MLST revealed a high diversity of C. concisus with 53 sequence types (STs), of which 52 were identified as 'new' STs. Allele sequences showed more than 90 % similarity between isolates, with only four outliers. Dendrogram profiles of each allele showed a division into two groups, which more or less correlated with genomospecies A and genomospecies B. However, in contrary to previous results, this subgrouping had no association to the clinical severity of disease.
