In vitro adherence of staphylococcus epidermidis to polymethyl methacrylate and acrysof intraocular lenses

Abstract

Purpose To investigate the adherence of one clinically relevant ocular isolate of Staphylococcus epidermidis to polymethyl methacrylate (PMMA) and Acrysof (Alcon Surgical, Fort Worth, TX) intraocular lenses (IOLs). Design Experimental study. Participants The authors examined the in vitro adherence of one clinically relevant ocular isolate of S. epidermidis. Adherence was tested on 12 PMMA IOLs and 12 Acrysof IOLs. Methods Six IOLs (three of each type) were placed in different test tubes containing bacterial suspension (10 8 cfu/ml) and incubated at 37°C. At different times (3 minutes, 30 minutes, and 90 minutes), each IOL type was removed from the test tube, rinsed in sterile phosphate-buffered saline, and transferred into sterile brain-heart infusion broth. The broth with the IOL was sonicated on low power for 3 minutes to remove adhered bacteria. Two serial 10-fold dilutions of the broth containing the dislodged bacteria were plated on mannitol agar plates. The plates were incubated overnight at 37°C and then bacterial colonies were counted. All assays were performed in triplicate. Additional lenses (three of each type) were incubated with S. epidermidis for different times (3 minutes, 30 minutes, and 90 minutes) and then examined with scanning electron microscopy. Main outcome measures The number of adhered bacteria per area (mm 2) of IOL optic was calculated. Statistical analysis included calculation of arithmetic means and 95% confidence intervals ( t test). Results Direct counting of viable adherent bacteria released by sonication showed that the amount of adhered bacteria per area of IOL optic after 3, 30, and 90 minutes’ incubation in S. epidermidis suspension was 0.1 × 10 2/mm 2, 3.6 × 10 2/mm 2, and 11 x 10 2/mm 2 (PMMA IOLs), and 4.4 × 10 2/mm 2, 3.1 × 10 2/mm 2, and 2.3 × 10 2/mm 2 (Acrysof IOLs). Direct counting of adherent bacteria in scanning electron microscopy photographs revealed that the total amount of adhered bacteria per area of IOL optic after 3, 30, and 90 minutes’ incubation in S. epidermidis suspension was 1.1 × 10 2/mm 2, 4.4 × 10 2/mm 2, and 5.5 × 10 2/mm 2 (PMMA IOLs) and 13 × 10 2/mm 2, 33.9 × 10 2/mm 2, and 72 × 10 2/mm 2 (Acrysof IOLs). Conclusions Results suggest that in vitro adherence of S. epidermidis to IOLs is influenced by IOL materials. After 3 minutes’ incubation, Acrysof IOLs appeared to be more permissive to S. epidermidis adherence than PMMA IOLs. The difference was statistically significant ( P < 0.05). However, at 90 minutes, Acrysof IOLs had a lower viable bacterial count than did the PMMA IOLs. Bacterial adherence appeared to be greater in areas with surface irregularities. Adherence of S. epidermidis to IOLs may play a role in the pathogenesis of some forms of endophthalmitis after cataract surgery.