Heparin, known for its anticoagulant activity, is commonly used in catheter locks. Staphylococcus aureus, a versatile human and animal pathogen, is commonly associated with catheter-related bloodstream infections and has evolved a number of mechanisms through which it adheres to biotic and abiotic surfaces. We demonstrate that heparin increased biofilm formation by several S. aureus strains. Surface coverage and the kinetics of biofilm formation were stimulated, but primary attachment to the surface was not affected. Heparin increased S. aureus cell-cell interactions in a protein synthesis-dependent manner. The addition of heparin rescued biofilm formation of hla, ica, and sarA mutants. Our data further suggest that heparin stimulation of biofilm formation occurs neither through an increase in sigB activity nor through an increase in polysaccharide intracellular adhesin levels. These finding suggests that heparin stimulates S. aureus biofilm formation via a novel pathway.

This in vitro study demonstrates that heparin alternatives, sodium citrate and sodium EDTA, can prevent the formation of S. aureus biofilms, suggesting that they may reduce the risk of biofilm-associated complications in indwelling catheters. This finding suggests a biological mechanism for the observed improvement in catheter-related outcomes in recent clinical comparisons of heparin and trisodium citrate as catheter locking solutions. A novel and potential clinically relevant finding of the present study is the observation that citrate at low levels strongly stimulates biofilm formation by S. aureus.

We reported previously that low concentrations of sodium citrate strongly promote biofilm formation by Staphylococcus aureus laboratory strains and clinical isolates. Here, we show that citrate promotes biofilm formation via stimulating both cell-to-surface and cell-to-cell interactions. Citrate-stimulated biofilm formation is independent of the ica locus, and in fact, citrate represses polysaccharide adhesin production. We show that fibronectin binding proteins FnbA and FnbB and the global regulator SarA, which positively regulates fnbA and fnbB gene expression, are required for citrate's positive effects on biofilm formation, and citrate also stimulates fnbA and fnbB gene expression. Biofilm formation is also stimulated by several other tricarboxylic acid (TCA) cycle intermediates in an FnbA-dependent fashion. While aconitase contributes to biofilm formation in the absence of TCA cycle intermediates, it is not required for biofilm stimulation by these compounds. Furthermore, the GraRS two-component regulator and the GraRS-regulated efflux pump VraFG, identified for their roles in intermediate vancomycin resistance, are required for citrate-stimulated cell-to-cell interactions, but the GraRS regulatory system does not impact the expression of the fnbA and fnbB genes. Our data suggest that distinct genetic factors are required for the early steps in citrate-stimulated biofilm formation. Given the role of FnbA/FnbB and SarA in virulence in vivo and the lack of a role for ica-mediated biofilm formation in S. aureus catheter models of infection, we propose that the citrate-stimulated biofilm formation pathway may represent a clinically relevant pathway for the formation of these bacterial communities on medical implants.Microorganisms commonly adhere to surfaces in multilayered groupings referred to as biofilms (29,54). Growth in a biofilm imparts particular properties to member organisms, including elevated levels of resistance to antibiotics and host defenses. Staphylococcus aureus, a common nosocomial pathogen known for its antibiotic resistance and its ability to cause a wide range of infections (43), can form biofilms on a number of medically relevant surfaces such as catheters and intraocular lenses (56,71,75). Biofilm formation by this microbe is thought to contribute to its ability to cause persistent infections (19,71,74).Most genetic studies of biofilm formation by S. aureus have involved the search for biofilm-defective mutants using laboratory medium, typically tryptic soy broth (TSB) supplemented with glucose. Such an approach has identified a number of genetic loci required for biofilm formation, including sarA, agr, dlt, hla, clp, and ica, which codes for the polysaccharide component of an extracellular biofilm matrix (9,25,27,45,55,66,72). The ica locus, its gene products, and the polysaccharide produced by the Ica proteins have been studied extensively in vitro (17, 44-46, 50, 53). A recent study reported a role for the ica locus of S. aureus in models of systemic infection and renal abscess infect...

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