Quantifying Pseudomonas aeruginosa Adhesion to Contact Lenses 1 Yen N.T. Dang, M.D., Aravinda Rao, M.D., Peter R. Kastl, M.D., Ph.D., Robert C. Blake II, Ph.D., Michael J. Schurr, Ph.D., and Diane A. Blake, Ph.D. Purpose. Pseudomonal keratitis can occur in soft contact lens wearers following compromise of the corneal epithelium and exposure to pathogens. This study was initiated to determine if Pseudomonas aeruginosa has the ability to adhere preferentially to unused contact lenses made from different FDA group polymers. Methods. Pseudomonas aeruginosa (strain PA01) was grown to its early stationary phase and diluted into phosphate-buffered saline to a concentration of 12,000 to 16,000 cells/mL. Samples from each of the four FDA-designated polymer classes used for the manufacture of soft lenses were incubated in pseudomonal inoc- ulant for 4 hours. The lenses were removed and the number of bacteria bound was quantified using electrical impedance particle counting. Results. A lens constructed from a group I polymer (nonionic polymer with 50% water) bound the fewest bacteria (7.2% of total cells  1.0 SD) whereas a lens made from group II polymers (nonionic polymer with 50% water) showed the high- est level of bacterial binding (42% of total cells  4.5 SD). Lenses constructed from group III and IV polymers showed intermediate levels of bacterial binding (28.4%  1.8 SD and 29.3%  1.7 SD, respectively). Conclusions. The polymer type used to construct the contact lens may influence subsequent bacterial adhesion events. Contact lenses made from nonionic polymers with high water content may carry higher risks of bacterial contamination. Key Words: Soft contact lenses—Bacterial adhesion—FDA poly- mer groups—Pseudomonas aeruginosa—Strain PA01—Electrical impedance particle counting—Contact lenses—Keratitis—Ionic— Nonionic. The development of corneal ulcers in individuals who wear soft contact lenses depends on a variety of contributing factors, includ- ing a compromised ocular surface (e.g., trauma from contact lens wear, hypoxia, dry eye), exposure to pathogens (e.g., poor hygiene, contact lens colonization of bacteria from extended wear), and virulence of the organisms. Pseudomonas aeruginosa is the most frequently found pathogen in corneal ulcers of patients who wear soft contact lenses. 1,2 Pseudomonal keratitis can progress rapidly to corneal perforation, with subsequent scarring and other sight- threatening complications. 1,3 P. aeruginosa binds to the corneal epithelial cell surface by pili proteins with the ability to bind to specific carbohydrate residues, and contact lens wear has been demonstrated to induce changes in the glycocalyx that increase the number of receptor sites. 4,5 Recent studies have shown that daily wear of soft contact lenses significantly increases the binding of P. aeruginosa to exfoliated epithelial cells and that this binding is inversely proportional to the oxygen transmissibility of the contact lens. 6 In addition, Sankaridurg et al. have reported a correlation between high levels of bacterial colonization of soft contact lens and episodes of corneal infiltrative events. 7 Previous investigations that used scanning electron microscopy to quantify bacterial ad- hesion in very small fields have studied the adhesion of P. aeruginosa to unused soft contact lenses constructed of polymacon (38.5% water, FDA group I) and lidofilcon (70% water, FDA group II). 8 The present report extends this study to all four FDA polymer groups and uses an electrical impedance particle counter to representatively sample the bacteria present in the incubation medium. MATERIALS AND METHODS P. aeruginosa strain PA01 was chosen because the complete genetic sequence is known. 9 Single colonies from Luria nutrient broth agar plates were inoculated into 100 mL of Luria nutrient broth and allowed to grow to the early stationary phase (18 to 24 hours) before being used in these experiments. Contact lenses from the four U.S. Food and Drug Administration (FDA) polymer groups (Table 1) were supplied by the manufacturers (Bausch & Lomb, Rochester, NY, and Wesley Jessen, Des Plaines, IL). All lenses were -3.00 power, with a base curve of 8.6 or greater, to minimize differences in surface area. When possible, the same manufacturer and similar polymers were also chosen to limit variability. Salts used to prepare buffers were purchased from Sigma Chemical Co. (St. Louis, MO). All buffer solutions used in these experiments were passed through 0.02-micrometer filters (Nalgenunc, Inc., Rochester, NY) immediately before use to elim- inate background particles. The stationary-phase cultures were diluted 1:100,000 (12,000 to 16,000 cells/mL) into phosphate-buffered saline (PBS) (137 mM NaCl, 2.7 mM KCl, 10 mM sodium phosphate, pH 7.2) containing 0.3% NaN 3 . Preliminary experiments showed that this concentra- 1 This work was supported by The O’Brien Ocular Pathology Fund, Department of Ophthalmology, Tulane University Health Sciences Center, and by a U.S. Department of Energy grant DE-FG02–96ER20228. Y.N.T. Dang and A. Rao contributed equally to this study. From the Departments of Ophthalmology (Y.N.T.D., A.R., P.R.K., and D.A.B.) and Microbiology (M.J.S.), Tulane University Health Sciences Center; and the College of Pharmacy, Xavier University of Louisiana (R.C.B.II), New Orleans, LA. . Address correspondence and reprint requests to: Dr. D.A. Blake, Depart- ment of Ophthalmology, SL-69, Tulane University Health Sciences Center, 1430 Tulane Avenue, New Orleans, LA 70112; Email: blake@tulane.edu. Accepted November 13, 2002. DOI: 10.1097/01.ICL.0000056624.83827.0E Eye & Contact Lens 29(2): 65–68, 2003 © 2003 Contact Lens Association of Ophthalmologists, Inc. 65