P12 – Effect of Lauric Acid on Staphylococcus aureus Biofilm Development

Author(s):

Donavon Hess, Michelle Henry-Stanley, Carol Wells, University of Minnesota

Background: Biofilms develop in a variety of clinical situations and the majority of infections are thought to involve biofilms, defined as microbial communities attached to a surface and encased in an extracellular polymeric substance. Biofilm-associated bacteria are less susceptible to antibiotics, often complicating treatment and necessitating removal of implanted devices. In Staphylococcus aureus biofilms, we have observed lipid structures which appear to play an important role in biofilm structure and antibiotic susceptibility of biofilm-associated bacteria.

Hypothesis: Because lipid structures can be disrupted by surfactants, we hypothesized that surfactants may disrupt biofilm development, and we noted that glycerol monolaurate (GML), a natural surfactant found in human breast milk, can prevent development of S. aureus biofilms. Because GML is made up of glycerol and lauric acid, experiments were designed to test the effect of lauric acid on S. aureus biofilm development.

Methods: S. aureus RN6390 or ATCC 25932 was inoculated onto 1-cm segments of 3-0 silk suture and incubated 16 hr in biofilm growth medium (66% tryptic soy broth plus 0.2% glucose) with or without lauric acid. Growth was assessed as viable colony forming units quantified from sonicated biofilms, and biomass was quantified with crystal violet staining. Data were analyzed by ANOVA with Fisher’s post hoc.

Results: Following incubation with 0, 0.313, 0.625, 1.25, 2.5 and 5 mM lauric acid, the numbers of viable biofilm-associated bacteria decreased resulting in avg log10 of 7.1, 6.1, 6.2, 3.9, 3.0, and <1.7, respectively, with all numbers decreased from control (no lauric acid) at P<0.01, and reflecting a 90% decrease with 0.313 mM lauric acid. Biofilm biomass was similarly decreased at P<0.01 in samples incubated with all concentrations of lauric acid. Similar results were obtained with S. aureus ATCC 25923 indicating that lauric acid-mediated inhibition of biofilm development was not limited to a single S. aureus strain.

Conclusions: . Lauric acid effectively prevented biofilm development as noted by a decrease in viable numbers of bacteria as well as in biofilm biomass. The mechanism of biofilm inhibition by lauric acid at the tested concentrations remains unclear, but could relate to disruption of biofilm structure formation (e.g. lipid structures), or interference with bacterial attachment. These findings suggest potential preventative or therapeutic adjuncts.