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Background: Infectious biofilms are recalcitrant to antimicrobial therapy, but the mechanism(s) responsible for the greater resistance are unclear. Experiments were designed to clarify the association between antibiotic resistance and biofilm ultrastructure.Methods: Staphylococcus aureus was cultivated for 24 h on silk suture, where robust biofilms formed. Initial experiments compared the susceptibilities of planktonic (free-living) cells and mechanically dispersed biofilm cells to ampicillin, oxacillin, and vancomycin. Antibiotics in bactericidal concentrations were then incubated overnight with 24-h biofilms, and subsequent assays determined the viability of cells in mechanically dispersed biofilms, biofilm metabolic capacity and biomass, and biofilm ultrastructure (scanning electron microscopy).Results: Planktonic and biofilm cells had similar intrinsic antibiotic susceptibility. Nonetheless, a stable population of bacteria remained viable after biofilms were incubated with inhibitory drug concentrations, although biofilm metabolic capacity often was not detected, and biomass generally was reduced. Electron microscopy revealed that control (no drug) biofilms consisted primarily of bacterial clusters amid fibrillar elements. Antibiotic-treated biofilms had some staphylococci with smooth cells walls similar to planktonic cells, but other cocci were encased in extracellular material. This material was more abundant in antibiotic-treated than in control biofilms.Conclusions: In the presence of high antibiotic concentrations, dense extracellular material may inhibit interaction of antibiotics with their bacterial targets. [ABSTRACT FROM AUTHOR]

Background: Bacterial biofilms are involved in a large proportion of clinical infections, including device-related infections. Unfortunately, biofilm-associated bacteria are typically less susceptible to antibiotics, and infected devices must often be removed. On the basis of a recent observation that lipid-rich biofilm matrix material is present in early biofilm formation and may protect a population of bacteria from interacting with ordinarily diffusible small molecules, we hypothesized that surfactants may be useful in preventing biofilm development., Methods: Experimental Staphylococcus aureus or Enterococcus faecalis biofilms were cultivated on surgical suture suspended in a growth medium supplemented with the natural surfactant glycerol monolaurate (GML) or with a component molecule, lauric acid. After 16 h incubation, the numbers of viable biofilm-associated bacteria were measured by standard microbiologic techniques and biofilm biomass was measured using the colorimetric crystal violet assay., Results: Both GML and lauric acid were effective in inhibiting biofilm development as measured by decreased numbers of viable biofilm-associated bacteria as well as decreased biofilm biomass. Compared with lauric acid on a molar basis, GML represented a more effective inhibitor of biofilms formed by either S. aureus or E. faecalis., Conclusions: Because the natural surfactant GML inhibited biofilm development, resulting data were consistent with the hypothesis that lipids may play an important role in biofilm growth, implying that interfering with lipid formation may help control development of clinically relevant biofilms.

Background: Although much attention is currently directed to studying microbial biofilms on a variety of surfaces, few studies are designed to study bacterial growth on surgical suture. The purpose of this study was to compare the kinetic development of Staphylococcus aureus and Enterococcus faecalis on five surgical suture materials and to clarify factors that might influence this growth., Methods: Pure cultures of S. aureus and E. faecalis were incubated with five types of suture for four days using either tissue culture medium or a bacterial growth medium. Suture-associated bacteria were quantified daily. In selected experiments, the bacterial growth medium was supplemented with heparin, a substance known to promote S. aureus biofilm formation. The ultrastructure of S. aureus biofilm developing on braided suture was studied with scanning electron microscopy., Results: Staphylococcus aureus and E. faecalis were recovered in greater numbers (typically p < 0.01) from braided than from monofilament suture, and the numbers of bacteria were greater (often p < 0.01) on sutures incubated in bacterial growth medium rather than tissue culture medium. Addition of heparin 1,000 U/mL to silk or braided polyglactin 910 suture incubated three days with S. aureus resulted in greater numbers of bacteria on day one but not on subsequent days. Scanning electron microscopy showed a maturing S. aureus biofilm that developed from small clusters of cells among amorphous material and fibrillar elements to larger clusters of cells that appeared covered by more consolidated extracellular material., Conclusions: Bacterial growth was favored on braided vs. monofilament suture, and heparin enhanced bacterial adherence after day one, but not at subsequent times. Staphylococcus aureus adhered to suture material and formed a structure consistent with a bacterial biofilm.