Background : The opportunistic pathogen Staphylococcus
aureus is a leading source of nosocomial infections. S.
aureus forms biofilms on a number of clinically relevant
surfaces including biomedical devices such as catheters. Figure
1 shows a S. aureus biofilm formed on catheter material. S.
aureus is a major problem in dialysis units where intravenous
catheters are commonly used.
Figure 1. SEM image of a S. aureus
biofilm formed overnight on silicon elastomer. Photograph taken
by Charles Daghlian, Dartmouth College EM Facility.
We found recently that the drug heparin can stimulate S.
aureus biofilm formation. Heparin is an anticoagulant
anionic polysaccharide made my mammalian cells. Preparations
of heparin are placed in catheters between dialysis sessions
to prevent clotting in and on the catheter. An unintended consequence
of the use of heparin in catheters may be an increased rate
of blood stream infection
Phenomenology : The presence of heparin strongly
enhances of S. aureus biofilm formation in a dose dependent
manner (Fig. 2). Heparin stimulates S. aureus biofilm
formation through cell-cell interactions rather than cell-surface
interactions. This enhancement in cell-cell interactions is dependent
upon protein synthesis. Heparin-induced biofilms are 60x more
resistant to vancomycin than planktonic cells.
Genetics : Heparin stimulates biofilms independently
of sarA , icaACBD , agr , spa , fnbAB , clfAB ,
and sigB . Heparin may allow us to find novel biofilm
factors and mutant hunts are currently underway.
Figure 2. Sodium heparin enhances S. aureus biofilm
formation. The effect of heparin on formation of S.
aureus (MZ100) biofilms on abiotic surfaces was assessed
microscopically. SEM micrographs of 12-hour old S. aureus biofilms
on PVC are shown with (B) and without heparin (A) (12,500x
magnification, bar = 10µm). S. aureus biofilms
(4 hours) formed on polystyrene were viewed with phase-contrast
microscopy (C and D, bar = 20µ, arrow indicates a phase
bright microcolony), or were stained with a fluorescent bacterial
stain (Styo-9) with a 250 ms exposure and at 400x magnification
with epifluorescent microscopy (E without heparin, and F with
heparin at 1000U/ml). 5-hour old biofilms were stained with EPS-binding
calcofluor and viewed with epifluorescent microscopy at 100x
magnification, with (H) and without heparin (G).
We have also published a recent set of studies
exploring the role of citrate, another anticoagulant used primarily
in Europe, in the stimulation and inhibition of biofilm formation
(see below).
Robert Shanks, a former post-doc in the lab, initiated
these studies and has recently started his own laboratory at
the University of Pittsburgh. Learn more about his work and some
new projects here.
To learn more about the role of heparin in
biofilm formation, please see the following references:
Shanks
RM, Donegan NP, Graber ML, Buckingham SE, Zegans ME, Cheung
AL, O'Toole GA. 2005. Heparin stimulates Staphylococcus aureus
biofilm formation. Infect Immun. 73:4596-606.
Shanks RM, Sargent JL, Martinez RM, Graber ML,
O'Toole GA. 2006. Catheter lock solutions influence staphylococcal
biofilm formation on abiotic surfaces. Nephrol Dial Transplant.
21(8):2247-55
