Adherence of Pseudomonas aeruginosa to shed rabbit corneal epithelial cells after overnight wear of contact lenses.

PURPOSE

Previous studies have shown that contact lens oxygen transmissibility correlates with binding of Pseudomonas aeruginosa to the rabbit cornea after overnight lens wear. Studies of human lens wear stratified by oxygen transmissibility will be required to validate these animal results. In humans, bacterial binding to shed cells obtained through corneal irrigation cytology may provide an indirect measure of in vitro binding. The purpose of this study was to establish the relationship between binding to shed cells and to the residual corneal surface in an animal model of lens wear prior to initiation of human studies.

METHODS

The test contact lenses used were: rigid lens A (Dk/L = 10 x 10(-9) [cm/ sec][mL O2/mL mmHg]); rigid lens B (Dk/L = 97); soft lens A (Dk/L = 9); soft lens B (Dk/L = 20); and, soft lens C (Dk/L = 39). There were six rabbits in each group, except for the soft lens C group, which had seven rabbits. After overnight lens wear, the corneal surface was irrigated with a corneal irrigation chamber to collect surface cells before exposure to a bacterial suspension (1 x 10(7) CFU/mL) for 30 minutes. The number of bacteria adherent to the residual corneal surface was then assessed by CFU determination. Cells collected from the corneal surface (9 mL) were incubated with 1 mL bacterial suspension containing 10(8) (CFU/mL) for 30 minutes. The number of bacteria adherent to shed cells was assessed by staining with acridine orange and direct counting by epifluorescence microscopy.

RESULTS

The differences in the number of bacteria adhering to shed epithelial cells between the treated and the control eyes were 2.90 +/- 1.20 and 0.23 +/- 0.41 for rigid lenses A and B, respectively, and 5.97 +/- 1.54, 3.67 +/- 2.32, and 0.90 +/- 1.45 (bacterial/cell) for soft lenses A, B, and C, respectively. Overnight contact lens wear induced a significant increase in bacterial binding to shed corneal epithelial cells for rigid lens A and for soft lenses A and B. There were significant differences among lens groups (P = 0.00017, ANOVA), with significant differences between rigid lenses A and B, soft lenses A and C, and soft lenses B and C. The binding of bacteria to shed cells was significantly correlated with the binding of bacteria to the residual corneal surface, both confirming and extending previous results (R = 0.78, P < 0.001).

CONCLUSION

These results demonstrate a positive correlation between P. aeruginosa adherence to shed corneal cells and to the residual corneal surface in the rabbit eye following contact lens wear. In light of the results from prior animal studies, examination of the behavior of P. aeruginosa binding to exfoliated cells appears to be a promising and valid method for future assessment of similar lens-induced increases in bacterial binding in prospective human clinical studies.