Research Article: Intestinal Bacteria Composition and Translocation of Bacteria in Inflammatory Bowel Disease

Date Published: January 18, 2017

Publisher: Public Library of Science

Author(s): Spyros Vrakas, Konstantinos C. Mountzouris, George Michalopoulos, George Karamanolis, George Papatheodoridis, Charalampos Tzathas, Maria Gazouli, Leonardo A. Sechi.


Live commensal intestinal bacteria are present in the peripheral blood where they can induce inflammation.

To evaluate the intestinal bacteria composition and translocation of bacteria in IBD.

Both blood and tissue biopsy samples were collected from adult patients with active/inactive Crohn’s disease (CD), active/inactive ulcerative colitis (UC) and healthy individuals. Most of the patients were newly diagnosed and none of them received antibiotics. Using a reverse transcription–quantitative real-time PCR (RT-qPCR) method, we determined the composition of microbiota. NOD2/CARD15 genotyping was also studied.

Total bacterial DNA concentration was increased in tissue and blood samples of IBD patients compared to healthy controls. Furthermore, the active IBD cases had higher total bacterial DNA concentration levels compared to the inactive cases. Three species characterized dysbiosis in IBD, namely an increase of Bacteroides spp in active and inactive IBD samples, and a decrease in Clostridium leptum group (IV), and Faecalibacterium prausnitzi in both active and inactive IBD patients. No significant association between bacterial translocation and NOD2/CARD15 mutations was found.

The composition of the microbiota in IBD patients differs from that of healthy controls. The high rate of bacterial DNA in the blood samples indicates translocation in inflammatory bowel disease.

Partial Text

The exact cause of Inflammatory bowel disease (IBD), consisting of Crohn’s disease (CD) and ulcerative colitis (UC) is unknown. However, IBD is thought to be driven by an abnormal immune response to intestinal microbiota in genetically predisposed individuals[1]. The intestinal microbiota is essential for the host energy balance, immune regulation and homeostasis, as well as for the host metabolism such as the breakdown of complex dietary carbohydrates, the mucus, and the production of organic acids to maintain an appropriate pH environment in the gut [2]. Dysbiosis of the intestinal microbiota has been shown in patients with several gastrointestinal disorders including IBD [3]. Additionally, several studies supported that the gut microbiota of patients with active IBD is depleted, is constituted of smaller number bacterial species, and in more unstable over time compared to those of patients with inactive IBD and healthy individuals [4,5]. Molecular analyses of the gut microbiota have also revealed differences in microbiota composition between CD and UC. Specifically, the gut microbiota in healthy people is dominated by the bacteria phyla Firmicutes, and Bacteroidetes and to a lesser extent by Proteobacteria, and Verrucomicrobia [6]. Concerning IBD, Wills et al [7] reported larger changes in the bacterial community composition between remission and exacerbation in CD patients in comparison to UC patients. Hansen et al [8] demonstrated an increase in Faecalibacterium prausnitzi, and a reduction in bacterial diversity in newly diagnosed pediatric CD patients but not in UC patients. Microbial changes were identified by biopsying colonic mucosa. Fyderek et al [9] showed a predominance of Streptococcus spp. in inflamed mucosa of CD adolescent patients, while Lactobacillus spp. were predominant in UC patients. Forbes JD et al [10] also found an increase in the levels of Bacteroidetes, and Fusobacteria in inflamed CD mucosa, although Proteobacteria, and Firmicutes were more frequently observed in inflamed UC patients. Gophna et al [11], and Bibiloni et al [12] showed a significant increase of Bacteroidetes in CD than in UC patients. However, in an Indian population, Kabeerdoss et al [13] found greater Bacteroides and Lactobacillus concentration in inflamed colonic mucosa of patients with UC in comparison to CD patients.

The clinical and analytical characteristics of patients included in the study are presented in Table 2.

In this study, we found that dysbiosis in a Greek population is significant among inflammed, non-inflammed and normal intestinal mucosa in healthy controls. We showed that the total concentration of bacterial DNA was higher in active IBD patients, both in both in intestinal tissue and blood, compared to non-active and healthy samples. No differences among inactive CD and UC cases and healthy controls were detected.