The influence of lens material and lens wear on the removal and viability of Staphylococcus epidermidis

https://doi.org/10.1016/j.clae.2008.01.003Get rights and content

Abstract

Purpose

The aim of this study was to evaluate the influence of lens material and lens wear on the removal capability of Staphylococcus epidermidis. Assessment of viability of remaining adhered bacteria was another goal of this work. Four silicone hydrogel materials (galyfilcon A, balafilcon A, lotrafilcon A, lotrafilcon B) and one conventional hydrogel material (etafilcon A) were assayed.

Methods

Detachment studies on S. epidermidis were carried out in a parallel plate flow chamber. Contact lenses (CLs) were fitted to the bottom of the flow chamber and a bacterial suspension was perfused into the system, promoting bacterial adhesion. Afterwards, detachment was stimulated using a multipurpose solution (MPS, ReNu Multiplus®) and the percentage of removed bacteria estimated through microscopic observation and enumeration. Remaining adhered bacteria were stained with propidium iodide (PI) and enumerated in order to assess their viability. Additionally, the worn lenses were observed by confocal laser scanning microscopy (CLSM) to visualize bacterial distribution along the lens surfaces.

Results

Bacterial removal was significant (p < 0.05) for both unworn and worn galyfilcon A and etafilcon A. Galyfilcon A exhibited a detachment percentage of 59.1 and 63.5 while etafilcon A of 62.6 and 69.3, both for unworn and worn lenses, respectively. As far as bacterial viability is concerned, it was found that worn lenses exhibit a superior amount of non-viable bacteria than unworn CLs. Images obtained by CLSM revealed an irregular bacterial distribution for all lens materials.

Conclusions

It appears that surface and/or bulk structure of the lens material affects removal of S. epidermidis while CL wear influences their viability.

Introduction

CL solutions were first produced in the late 40s and have been developed ever since. These solutions should comprise several functions as to enhance CL wettability, prevent the build-up of deposits and provide effective disinfection against pathogenic microorganisms [1]. Currently, MPS are the most popular CL solutions since they permit in a single step to clean, rinse and disinfect [2]. Disinfection is mainly promoted by the presence of biocides and it is essential to prevent ocular infections, which ultimately can lead to vision impairment. This process may be affected by numerous factors, which include the biocide, the challenging microbe, the material and the presence of organic matter [3], [4], [5], [6]. Due to the presence of surfactants, MPS may also promote bacterial removal; however, according to a previous study it was not significant [7].

Polyhexamethylene biguanide (PHMB) is one of the most popular biocide agents and has been used since the mid 70s in ophthalmic solutions. It is a polymeric cationic surfactant that belongs to the biguanide family and is currently used in several commercially available MPS. PHMB performs by enabling membrane disruption and lysis in bacteria, which results in their death [8], [9].

Several studies have investigated disinfection and bacterial detachment from CLs [7], [10], [11], [12], [13], [14], [15], [16], [17]. However, since silicone hydrogel CLs were launched, very few works have been performed with this type of material. The present study aimed to evaluate the influence of lens material and lens wear on the detachment capability of Staphylococcus epidermidis. Four silicone hydrogel materials (galyfilcon, balafilcon A, lotrafilcon A, lotrafilcon B) and one HEMA material (etafilcon A) were worn daily, for one month with nightly disinfection with a single multipurpose solution (ReNu Multiplus). In addition, viability and distribution of the remaining adhered bacteria were analysed through epifluorescence microscopy and CLSM, respectively. Matched unworn lenses served as the control.

Section snippets

Contact lenses

The CLs used in this study are detailed in Table 1.

Clinical trial

Thirty-one subjects from both genders enrolled the present study, excluding any lost to follow up. The volunteers were predominantly from the north of Portugal and the average age was 23.6 ± 5.5 years. These were chosen according to the following parameters: they have never worn CLs before (neophytes), they were not taking any medications during the trial, they did not suffer from any kind of ocular allergy and they had no tendency for dry eye

Bacterial detachment

The percentage of removed bacteria is detailed in Table 2. According to statistical analysis, bacterial removal was significant for galyfilcon A and etafilcon A materials. Both unworn galyfilcon A and etafilcon A showed p = 0.029, while worn galyfilcon A and etafilcon A exhibited p = 0.006 and p < 0.001, respectively.

Cell viability

Table 2 also presents the percentage of non-viable cells that remained adhered after the passage of the MPS. This percentage was higher for worn CL, ranging from 23.0% (3.50E5 cells/cm2)

Discussion

The present study investigated the influence of lens material and wear on the removal and viability of adhered S. epidermidis to silicone and conventional hydrogel CL. A single PHBM-based solution was used. S. epidermidis is a pathogen normally associated to device-related infections and thus it was considered an appropriate challenging microorganism [20], [21], [22]. Bacterial disinfection and detachment are two different concepts, but both important from a clinical perspective. While

Acknowledgements

The authors fully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) through the project POCTI/FCB/44628/2002 and also the grant BD 19679/2004 (FCT).

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