Adherence and kinetics of biofilm formation of Staphylococcus epidermidis to different types of intraocular lenses under dynamic flow conditions.

PURPOSE: To compare the adherence and biofilm formation of Staphylococcus epidermidis under in vitro flow conditions on intraocular lenses (IOLs) made of 4 biomaterials: poly(methyl methacrylate) (PMMA), silicone, hydrophilic acrylic, and hydrophobic acrylic. SETTING: Department of Ophthalmology, Croix-Rousse University Hospital and University Research Laboratory, Lyon, France. METHODS: Intraocular lenses were placed in a bioreactor designed to replicate intraocular conditions. The model consisted of Tygon tubing connected to a vial. Three septa allowed the entry and elimination of the artificial aqueous humor and inoculation of the bacterial suspension. The first of 2 pumps moved the aqueous humor along the circuit; the second pump regulated the flow at which the nutritive environment was regenerated. At various times (12, 16, 24, 40, 48, 60, and 72 hours), IOLs were taken from this environment and the bound bacteria were removed and counted. The distribution of bacterial adhesion on the IOLs was modeled using polynomial Poisson regression. To test the effect of the IOL biomaterial on bacterial adhesion, likelihood ratio tests were performed. RESULTS: The model provided the kinetics of S epidermidis biofilm growth on IOLs. The biofilm growth on each of the 4 biomaterials occurred in 3 phases: latent, dynamic or accelerated growth, and linear growth. The extent of bacterial binding to IOLs increased from hydrophilic acrylic polymer to PMMA, hydrophobic acrylic, and silicone. The differences were statistically significant. CONCLUSION: Bacterial adhesion to and biofilm development on the IOL surface depended on the characteristics of the biomaterial.

A novel in vitro model to study staphylococcal biofilm formation on intraocular lenses under hydrodynamic conditions.

PURPOSE: To develop a novel in vitro model to study the formation of Staphylococcus epidermidis biofilm on intraocular lenses (IOLs) from the primary-attachment phase to the biofilm-accumulation phase. The model was designed to replicate intraocular conditions especially by taking into account intraocular hydrodynamics. METHODS: The model consisted of Tygon tubing connected to a vial containing acrylic hydrophobic IOLs. Three septa, placed along the tubing, allowed, respectively, the artificial aqueous humor's arrival and its elimination and the bacterial suspension's inoculation. A first pump allowed the aqueous humor's movement along the circuit, whereas a second one regulated the flow at which the nutritive environment was regenerated. The whole circuit was placed in a 34 degrees C water bath. Every 2 to 4 hours, lenses were taken from this environment. Bound bacteria were removed by scraping of optical faces and counted. All data are presented as the mean, SD, and coefficient of variation (CV). Comparisons among experiments were performed by one-way analysis of variance (ANOVA). RESULTS: Calculated CVs were close to 30, showing that biofilm formation was homogeneous. Differences between experiments were nonsignificant for each removal time. The model provided the full kinetics of S. epidermidis biofilm growth on acrylic hydrophobic IOLs, with a stationary phase reached after 28 hours of incubation. CONCLUSIONS: Biofilm development is modulated by many variables, including environmental factors. The findings in the present study of bacterial colonization of IOLs under intraocular physiological conditions allow understanding and more accurate targeting of biomedical device-related infections such as endophthalmitis.

Antibacterial activity of clonidine and neostigmine in vitro.

We conducted an in vitro study to investigate the antibacterial activity of clonidine and neostigmine on common microorganisms encountered during infectious complications after regional anesthesia. Standardized suspensions of Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli were incubated during 1, 3, 6, and 24 h at 37 degrees C with concentrations of 37.5, 75, and 150 microg/mL of clonidine and 125, 250, and 500 microg/mL of neostigmine. After 24 h incubation at 37 degrees C, the colony counts were compared by two-way analysis of variance. The mean colony counts for S. aureus decreased significantly from control as the exposure to clonidine increased (P < 0.05), with a approximately 100% kill at 6 h for the largest concentration (150 microg/mL) and at 24 h for the intermediate concentration (75 microg/mL). Similar results were observed for S. epidermidis, with a approximately 100% kill at 6 h for the largest concentrations (75 and 150 microg/mL). No bactericidal activity of clonidine was observed for E. coli and no bactericidal activity of neostigmine was observed for any of the tested strains. In the conditions of this experiment, clonidine, but not neostigmine, exhibited a concentration-dependent and time-dependent bactericidal activity in vitro on the microorganisms most frequently encountered in infectious complications after regional anesthesia.