Preliminary study on bacterial translocation in serum of patients with inflammatory bowel disease

Abstract

The pathogenesis of inflammatory bowel disease (IBD) involves the interaction between genetic susceptibility, mucosal immunity and intestinal bacteria. Bacterial DNA (bact DNA) derived from luminal bacteria may contribute to the perpetuation of chronic intestinal inflammation. Blood microbiological cultures, though, are frequently negative in these patients and bacterial translocation episodes may be put out of sight. To evaluate the presence of bacterial translocation in patients with IBD by means of detection of bacterial DNA in blood. 23 patients with IBD not treated with antibiotics the month before inclusion were considered in the study and distributed into the following groups: Group I: active Crohn's disease (CD); Group II: inactive CD; Group III: active ulcerative colitis (UC); and Group IV: inactive UC. A blood sample was collected in endotoxin-freetubes and a broad-range PCR of a highly conserved region of the bacterial 16SrRNA gene was performed using the following primers: 5′-TTCCGGTTGATC-CTGCCGGA-3′ as forward, and 5′-GGTTACCTTGTTACGACTT-3′ as reverse. Bacterial genomic fragments were purified (QIAquick, QIAgen) and identified by automated nucleotide sequencing analysis (ABIPRISM 310, Applied Biosystems). Sequence alignments were carried out with NCBI database (www.ncbi.nih.gov), using the advanced BLAST search tool. Microbiological cultures were carried out among all the patients. the number of patients studied and the percentage of patients with bacterial DNA are detailed in Table 1, according to previously mentioned group distribution. Bacteria identifications included E. coli, Enterococcus spp and Staphylococcus spp. Blood cultures were negative in all cases. Molecular detection tools in patients with IBD are able to identify a subgroup of patients with presence of circulating bacterial DNA that remain undetected by microbiological culture. The presence of bacterial translocation in patients with inactive CD, the surprising prevalence of bacterial DNA from Enterococcus spp in patients with active UC, and the likely existence of immune consequences associated to these facts require new investigations.