Editors' ChoiceInfectious Disease

Bacterial Breakaway

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Science Translational Medicine  26 Jan 2011:
Vol. 3, Issue 67, pp. 67ec12
DOI: 10.1126/scitranslmed.3002148

Hospitalized patients often need indwelling catheters. However, the contamination of such medical devices by microbes that normally inhabit the human skin is a major contributor to hospital-acquired infections in patients. The principal culprit is the bacterium Staphylococcus epidermidis, which is part of the skin flora of patients and hospital personnel alike. This bacterium attaches to a catheter and then forms a biofilm (a cluster of bacteria embedded in an extracellular matrix). Biofilm formation helps invading microbes to resist the host immune system and the onslaught of antimicrobial drug treatment. Furthermore, dissemination of bacteria from the catheter-associated biofilm may lead to systemic infection of the patient. However, the molecular mechanisms underlying detachment of S. epidermidis from biofilms during infection are unclear. Enter Wang et al., who now reveal that S. epidermidis produces surfactant peptides called phenol-soluble modulins (PSMs) that are important mediators of bacterial detachment from biofilms.

The researchers first showed that S. epidermidis produces β-type PSM peptides in culture. Low concentrations of these peptides increased biofilm formation, whereas higher concentrations promoted detachment of the bacteria and a reduction in biofilm size. Next, the investigators developed a mouse model of catheter-related infection by inserting under the dorsal skin of mice pieces of catheter partially covered with a biofilm produced by S. epidermidis. They found that the catheter pieces covered in an S. epidermidis biofilm enabled systemic dissemination of these bacteria into the lymph nodes and body fluids of the mice. In contrast, mutant strains of S. epidermidis that could not produce PSM peptides showed an impaired ability to detach from their catheter-associated biofilm, resulting in reduced dissemination. This implies that PSM peptides are required for S. epidermidis to detach from the biofilm and to set up a systemic infection.

With their elegant mouse model of biofilm-contaminated catheters, Wang et al. clearly show that PSM peptides produced by S. epidermidis enable this invasive microbe to detach from the biofilm on the contaminated catheter and set up a systemic infection in the host. From a therapeutic perspective, blocking PSM peptides should prevent bacterial dissemination from biofilms, although this could increase the size of the biofilm. Nevertheless, this important study provides new insights into how device-related infections in hospitalized patients could be prevented.

R. Wang et al., Staphylococcus epidermidis surfactant peptides promote biofilm maturation and dissemination of biofilm-associated infection in mice. J. Clin. Invest. 121, 238–248 (2011). [Full Text]

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