Different antimicrobial activity of beta defensins and colonic biopsy extracts against aerobic and anaerobic bacterial strains of the gastrointestinal tract

Abstract number: 1733_301

Nuding S., Zabel L., Fellermann K., Wehkamp J., Mueller H.A.G., Stange E.F.

Objectives: The human gastrointestinal tract harbours a variety of aerobic and anaerobic microorganisms. To prevent colonisation and invasion of bacteria, the intestinal mucosa synthesizes antimicrobial peptides such as the cationic defensins. Based on RT-PCR and western blot, we determined a high induction of beta defensins in ulcerative colitis, whereas beta defensins in Crohn's disease were less induced. To elucidate possible functional consequences for the intestinal barrier, we investigated the antimicrobial activity of defensins and cationic protein extracts, taken from the colon of patients with Crohn's disease, ulcerative colitis or controls, against bacteria of the intestinal flora.

Methods: To quantitate the antimicrobial activity, we established a flow cytometric assay with the membrane potential sensitive dye bis-(1,3-dibutylbarbituric acid) trimethine oxonol. Depolarisation of the bacterial cell membrane caused by antimicrobial peptides leads to an uptake of the dye followed by an increasing green fluorescence. We tested the antibacterial activity of the constitutive human beta defensin HBD-1, the inducible defensin HBD-3 and cationic biopsy extracts of 22 patients with colonic Crohn's disease, 32 with ulcerative colitis and 13 controls against ATCC strains of Escherichia coli and Staphylococcus aureus and a clinical isolate of Bacteroides vulgatus.

Results: In populations of the aerobic strains E. coli and S. aureus as well as the anaerobic strain B. vulgatus 80% of the bacteria were killed by 2.5–5 mg HBD-3/mL. In contrast, HBD-1 in concentrations up to 15 mg/mL, which kill E. coli and S. aureus, exerted no bactericidal effect against B. vulgatus. The antimicrobial activity of cationic biopsy extracts was significantly diminished in extracts of patients with Crohn's disease against E. coli and B. vulgatus compared to ulcerative colitis. The activity in extracts of Crohn's disease against S. aureus was also reduced, but the differences versus controls and ulcerative colitis were less pronounced.

Conclusion: The viability of B. vulgatus is not influenced by the constitutive HBD-1, this is in concordance with its augmented presence in the normal intestinal flora. The inducible defensin HBD-3 is a potent antimicrobial peptide against all 3 strains tested. The lower antimicrobial activity in extracts of Crohn's disease corresponds well to the deficient beta defensin induction. The impact of other antimicrobial peptides must still be clarified.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
Back to top