The Natural Surfactant Glycerol Monolaurate Significantly Reduces Development of Staphylococcus aureus and Enterococcus faecalis Biofilms

Abstract

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.

FIG. 1.

Effect of glycerol monolaurate (GML) on development of Staphylococcus aureus RN 6390 and ATCC 25923 biofilms incubated 16 h on silk suture, as measured by the numbers of viable biofilm bacteria (A) and biofilm biomass (B). Each data point represents 12 biofilms. Dashed line represents the lower limit of assay detection. *, decreased at p<0.01 compared with corresponding 0 mM GML.

FIG. 2.

Phase contrast micrographs of silk suture incubated 16 h with Staphlococcus aureus RN 6390 cultivated in growth medium alone (A) or in growth medium supplemented with 0.35 mM GML (B). Scale bar is 200 μm.

FIG. 3.

Effect of lauric acid on development of Staphylococcus aureus RN 6390 and ATCC 25923 biofilms incubated 16 h on silk suture, as measured by the numbers of viable biofilm bacteria (A) and biofilm biomass (B). Each data point represents 12 biofilms. Dashed line represents the lower limit of assay detection. *, decreased at p<0.01 compared with corresponding 0 mM lauric acid.

FIG. 4.

Effect of glycerol monolaurate (GML) (A) and lauric acid (B) on development of Enterococcus faecalis OG1RF and VA1128 biofilms incubated 16 h on silk suture, as measured by the numbers of viable biofilm bacteria. Each data point represents 8 biofilms. Dashed line represents the lower limit of assay detection. *, decreased at p<0.01 compared with corresponding 0 mM GML or lauric acid.