Staphylococcus epidermidis Uses Distinct Mechanisms of Biofilm Formation To Interfere with Phagocytosis and Activation of Mouse Macrophage-Like Cells 774A.1

Abstract

ABSTRACTAssembly of adherent biofilms is the key mechanism involved inStaphylococcus epidermidisvirulence during device-associated infections. Aside from polysaccharide intercellular adhesin (PIA), the accumulation-associated protein Aap and the extracellular matrix binding protein Embp act as intercellular adhesins, mediatingS. epidermidiscell aggregation and biofilm accumulation. The aim of this study was to investigate structural features of PIA-, Aap-, and Embp-mediatedS. epidermidisbiofilms in more detail and to evaluate their specific contributions to biofilm-relatedS. epidermidisimmune escape. PIA-, Embp-, and Aap-mediated biofilms exhibited substantial morphological differences. Basically, PIA synthesis induced formation of macroscopically visible, rough cell clusters, whereas Aap- and Embp-dependent biofilms preferentially displayed a smooth layer of aggregated bacteria. On the microscopic level, PIA was found to form a string-like organized extracellular matrix connecting the bacteria, while Embp produced small deposits of intercellular matrix and Aap was strictly localized to the bacterial surface. Despite marked differences,S. epidermidisstrains using PIA, Aap, or Embp for biofilm formation were protected from uptake by J774A.1 macrophages, with similarly efficiencies. In addition, compared to biofilm-negativeS. epidermidisstrains, isogenic biofilm-formingS. epidermidisinduced only a diminished inflammatory J774A.1 macrophage response, leading to significantly (88.2 to 88.7%) reduced NF-κB activation and 68.8 to 83% reduced interleukin-1β (IL-1β) production. Mechanical biofilm dispersal partially restored induction of NF-κB activation, although bacterial cell surfaces remained decorated with the respective intercellular adhesins. Our results demonstrate that distinctS. epidermidisbiofilm morphotypes are similarly effective at protectingS. epidermidisfrom phagocytic uptake and at counteracting macrophage activation, providing novel insights into mechanisms that could contribute to the chronic and persistent course of biofilm-relatedS. epidermidisforeign material infections.