Characterization of the importance of polysaccharide intercellular adhesin/hemagglutinin of Staphylococcus epidermidis in the pathogenesis of biomaterial-based infection in a mouse foreign body infection model

Abstract

The production of biofilm is thought to be crucial in the pathogenesis of prosthetic-device infections caused by Staphylococcus epidermidis. An experimental animal model was used to assess the importance of biofilm production, which is mediated by polysaccharide intercellular adhesin/hemagglutinin (PIA/HA), in the pathogenesis of a biomaterial-based infection. Mice were inoculated along the length of a subcutaneously implanted intravenous catheter with either wild-type S. epidermidis 1457 or its isogenic PIA/HA-negative mutant. The wild-type strain was significantly more likely to cause a subcutaneous abscess than the mutant strain (P < 0.01) and was significantly less likely to be eradicated from the inoculation site by host defense (P < 0.05). In addition, the wild-type strain was found to adhere to the implanted catheters more abundantly than the PIA/HA-negative mutant (P < 0.05). The reliability of the adherence assay was assessed by scanning electron microscopy. To exclude contamination or spontaneous infection, bacterial strains recovered from the experimental animals were compared to inoculation strains by analysis of restriction fragment length polymorphism patterns by pulsed-field gel electrophoresis. In vitro binding of the wild-type strain and its isogenic mutant to a fibronectin-coated surface was similar. These results confirm the importance of biofilm production, mediated by PIA/HA, in the pathogenesis of S. epidermidis experimental foreign body infection.

FIG. 1

Subcutaneous abscess formation by S. epidermidis 1457 and isogenic PIA/HA-negative mutant 1457-M10 in the mouse foreign body infection model. Visually apparent abscesses developed in 40 and 67% of animals inoculated with 10⁶ and 10⁷ CFU, respectively, of the wild-type S. epidermidis 1457 compared to 0 and 13% of animals inoculated with equal numbers of S. epidermidis 1457-M10. Of animals inoculated with 10⁸ CFU of S. epidermidis 1457-M10, 20% developed a subcutaneous abscess. Bars represent the mean abscess formation, and the lines represent the standard error of the mean.

FIG. 2

Appearance of representative animals on day 7 in the foreign body infection models that were inoculated with 10⁷ CFU of S. epidermidis 1457 (a) and 10⁷ CFU of the PIA/HA-negative mutant S. epidermidis 1457-M10 (b). An obvious subcutaneous abscess is evident in the strain 1457-infected mouse. The surgical site (arrow) is well healed in the strain 1457-M10-infected mouse, and there are no signs of inflammation or abscess formation.

FIG. 3

Recovery of S. epidermidis 1457 and its isogenic PIA/HA-negative mutant 1457-M10 from implanted subcutaneous catheter segments in the mouse foreign body infection model. There were significantly greater numbers of strain 1457 adherent to the catheters compared to strain 1457-M10 at both the 10⁶ and 10⁷ CFU inoculum levels. Although there were fewer bacteria recovered from the catheters of mice inoculated with 10⁸ CFU of S. epidermidis 1457-M10 than from the catheters of mice inoculated with either 10⁷ or 10⁶ CFU of S. epidermidis 1457, these differences did not reach statistical significance. Bars represent the mean of log-transformed adherence values, and the lines represent the standard error of the mean. cath, catheter.

FIG. 4

Binding of S. epidermidis 1457 and its isogenic PIA/HA-negative mutant 1457-M10 to immobilized fibronectin. Bacterial suspensions of both strains were applied to microtiter wells coated with 1 μg of fibronectin per ml and to uncoated control wells. Attached cells were detected by ELISA. A representative experiment is shown.