Some potential pathogenic traits of gram-negative bacteria isolated during ocular inflammation and infections

Background : Bacterial colonisation of contact lenses is believed to be important in the production of microbial keratitis and acute inflammatory reactions. The aim of the current study was to examine strains isolated from ocular infections and non-infectious ocular inflammatory conditions for their ability to adhere to contact lenses and epithelial cells and to stimulate the release of chemotactic substances from epithelial cells. Methods : Bacterial adhesion to contact lenses and bovine corneal or conjunctival cells was studied by adhesion assay. Agglutination of human red blood cells by bacteria was demonstrated by haemagglutination. The chemoattractants released from corneal epithelial cells exposed to bacteria was assessed by polymorphonuclear leukocytes (PMN) chemotaxis. Results : Strains of P. aeruginosa adhered better on the contact lenses than strains of other gram-negative bacteria (p = 0.004). H. influenzae strains isolated from conjunctivitis produced haemagglutination. Leukotriene B₄ was released from corneal epithelial cells after stimulation by the gram-negative bacteria. Conclusion : This study has identified several potential pathogenetic traits of gram-negative bacteria that may contribute to ocular infection and/or inflammation. It has been estimated that 70 per cent of microbial keratitis cases associated with contact lens wear involve P. aeruginosa and this study has shown that this bacterial species adheres in large numbers to contact lenses. This increased adhesion to contact lenses may be one of the reasons for the preponderance of this species in these infections. The finding that strains could stimulate corneal epithelial cells to release chemotactic factors that specifically recruit PMN indicates a mechanism for producing corneal infiltration.     

Serotype and adhesion of Pseudomonas aeruginosa isolated from contact lens wearers

The purpose of the present study was to correlate the serotypes of Pseudomonas aeruginosa to the bacterial adhesion to contact lenses and human corneal epithelial cells. Twenty‐three strains isolated from contact lens wearers were used for the study. The bacterial serotypes were examined with a P. aeruginosa antisera kit. The attachment of bacteria on contact lenses or human corneal epithelial cells was determined by counting the number of adhered bacteria after incubation of the bacteria with contact lenses or corneal epithelial cells. The 23 ocular isolates belonged to seven serotypes. Strains of serotypes I, G and E were the three dominant serogroups and were more adhesive to contact lenses compared with other groups of the bacteria. The bacterial serotypes and the clinical sequelae were not strongly related. These results indicate that the surface characteristics of bacterial serotypes are related to the bacterial adhesion to the surface, but the pathogenesis of the bacteria may result from multiple factors.     

The effect of protein-coated contact lenses on the adhesion and viability of gram negative bacteria

PURPOSE: Gram negative bacterial adhesion to contact lenses can cause adverse responses. During contact lens wear, components of the tear film adsorb to the contact lens. This study aimed to investigate the effect of this conditioning film on the viability of bacteria. METHODS: Bacteria adhered to contact lenses which were either unworn, worn for daily-, extended- or overnight-wear or coated with lactoferrin or lysozyme. Numbers of viable and total cells were estimated. RESULTS: The number of viable attached cells was found to be significantly lower than the total number of cells on worn (50% for strain Paer1 on daily-wear lenses) or lactoferrin-coated lenses (56% for strain Paer1). Lysozyme-coated lenses no statistically significant effect on adhesion. DISCUSSION: The conditioning film gained through wear may not inhibit bacterial adhesion, but may act adversely upon those bacteria that succeed in attaching.     

The ability of ocular bacteria to bind to fibronectin

Background : Fibronectin enters the tear film during sleep and on reflex tear stimulation. Also, contact lens wearers with increased levels of fibronectin in their tears are more likely to carry greater numbers of bacteria on their contact lenses. This points to a role of fibronectin in mediating adhesion of bacteria to contact lenses. Methods : Bacterial strains isolated from the eyes of contact lens wearers were examined for their ability to bind to fibronectin. Fibronectin binding was examined in solution or adsorbed onto a surface. Results : A strain of Pseudomonas aeruginosa isolated at the time of an acute keratitis and a strain of Stenotrophomonas maltophilia isolated from an asymptomatic eye adhered to soluble or adsorbed fibronectin by greater amounts than other species tested (p < 0.01). Using fibronectin derived from plasma (pFn) and fibronectin derived from cells (cFn) it was shown that the addition of cFn in the presence of pFn increased the binding of pFn to cells indicating aggregation or co-operativity in binding between the two fibronectin types to the cell surface. P. aeruginosa probably bound to both the protein and carbohydrate moieties of fibronectin. Protein(s) on the cell surface of P. aeruginosa probably mediated the adhesion as digestion of cells with protease significantly (p < 0.01) reduced binding. Conclusions : Bacteria isolated from contact lenses, and in particular gram-negative bacteria implicated in the production of keratitis, are able to bind to fibronectin. Also, different types of gram-negative bacteria had distinct abilities to adhere to fibronectin. This may have implications in the binding of these strains to contact lenses in vivo.     

Role of tear fluid in the growth of Gram-negative bacteria on contact lenses

Incidents of CLARE (contact lens induced acute red eye) are associated with high numbers of Gram-negative bacteria on the lens surface. This study found that most strains of bacteria implicated in CLARE adhere poorly to the lens surface regardless of whether the lens surface was clean or had been worn in the eye. The high numbers of bacteria on the lens surface result from bacterial growth on the lens surface after adhesion has occurred. Using an artificial tear formulation and real tears, this study demonstrated that the tear fluid provides the necessary nutrients required for bacterial growth.     

Tear film,contact lenses and tear biomarkers

This article summarises research undertaken since 1993 in the Willcox laboratory at the University of New South Wales, Sydney on the tear film, its interactions with contact lenses, and the use of tears as a source of biomarkers for ocular and non‐ocular diseases. The proteome, lipidome and glycome of tears all contribute to important aspects of the tear film, including its structure, its ability to defend the ocular surface against microbes and to help heal ocular surface injuries. The tear film interacts with contact lenses in vivo and interactions between tears and lenses can affect the biocompatibility of lenses, and may be important in mediating discomfort responses during lens wear. Suggestions are made for follow‐up research.     

Induction of cytokines from polymorphonuclear leukocytes and epithelial cells by ocular isolates of Serratia marcescens

PURPOSE: During contact lens wear, bacterial contamination of the lens can lead to the development of microbial keratitis (MK) or contact lens induced acute red eye (CLARE). Inflammatory mediators released by the host may heighten the response. We have examined the ability of human corneal epithelial cells and polymorphonuclear leukocytes (PMNs) to release cytokines upon stimulation with bacteria. METHODS: Serratia marcescens strains were added to corneal epithelial cells or PMNs. After incubations of up to 20 hours, supernatants were assayed for the presence of inflammatory mediators by ELISA. RESULTS: All strains stimulated PMNs to release IL-8 and LTB(4). Epithelial cells did not release LTB(4). IL-8 was released after exposure to most S. marcescens isolates. A sub-group of strains stimulated the release of TNF-alpha from corneal epithelial cells. CONCLUSIONS: S. marcescens can stimulate the release of inflammatory mediators from both PMNs and corneal epithelial cells. This release could be important in the progression and resolution of MK and CLARE.     

Effect of tear-specific immunoglobulin A on the adhesion of Pseudomonas aeruginosa I to contact lenses.

PURPOSE: The aims of the study were (i) to determine the immunodominant antigens of Pseudomonos aeruginoso 1 (Paer1) to tear secretory immunoglobulin A (sIgA); (ii) to study the role of sIgA in inhibiting bacterial adhesion to contact lenses. METHODS: SDS-PAGE and Western blotting were used to study the interaction of tear sIgA with Paer1; an adhesion assay was used to study the effect of sIgA on the adhesion of Paer1 to the contact lenses. RESULTS: The results of our study showed that the immunodominant molecules of Paer1 which reacted with tear sIgA were of molecular masses of 105, 50, 45 kDa; the binding of sIgA to Paer1 resulted in a reduction of the adhesion of Paer1 to worn Etafilcon A contact lenses. CONCLUSIONS: In conclusion, Paer1-specific sIgA are present in tears; the immunodominant molecules of Paer1 may be adhesins and tear-specific sIgA might play an important role in protecting the eye from contact-lens-induced corneal infection by preventing bacterial attachment to contact lenses and the ocular surface.     

Adherence of Acanthamoeba castellanii cysts and trophozoites to unworn soft contact lenses

Contact lens-related Acanthamoeba keratitis has been associated with the use of soft contact lenses and homemade saline solutions. We studied the adherence of Acanthamoeba to unworn extended-wear soft contact lenses on a human corneal isolate of Acanthamoeba castellanii suspended in normal saline (cysts, 6.3 x 10(5)/ml; trophozoites, 3.6 x 10(5)/ml). Unworn hydrogel contact lenses (polymacon, water content 38.6%; 50 lenses, 400 lens segments) were exposed to A. castellanii cysts or trophozoites with or without stirring. After exposure for zero to seven hours, soft contact lenses were or were not washed, and the A. castellanii adherence was determined with a standardized light-microscopy technique (40 fields, ten lens segments for each count) and with scanning electron microscopy. Both cysts and trophozoites adhered to the unworn soft contact lenses. Trophozoites showed acanthopodia, lobopodia, and filopodia. This study indicates that both A. castellanii cysts and trophozoites can firmly adhere to unworn soft contact lens. Such adherence may play a role in the pathogenesis of soft contact lens-related Acanthamoeba keratitis.     

Contact lens surface deposits increase the adhesion of Pseudomonas aeruginosa

Soft contact lenses are bathed with tear components during wear and surface deposits accumulate. This report shows that Pseudomonas aeruginosa adheres to the surface of worn extended wear contact lenses in direct proportion to the amount of lens surface deposits as determined by the Rudko method (P less than .05). More hydrophobic bacteria adhered 10 times greater than bacteria which were relatively hydrophilic (P less than .005). The effect upon bacterial adhesion of enzyme and surfactant cleaning of worn extended wear contact lenses was investigated by two independent methods: one involving a high inoculum and the other a low inoculum of Pseudomonas. Treatment of worn lenses with commercially available enzymes such as papain and pork pancreatin as well as treatment with neuraminidase, mannosidase, glucosidase and alkylcarboxylic acid for as long as 48 hours failed to reduce subsequent bacterial adhesion in both the high and low inoculum experiments. We conclude that soft contact lens surface deposits are a major determinant in the adhesion of Pseudomonas aeruginosa to the worn lens surface and that enzyme cleaning of worn lenses does not significantly reduce bacterial adhesion.     

Diabetes and contact lens wear

The literature suggests that diabetic patients may have altered tear chemistry and tear secretion as well as structural and functional changes to the corneal epithelium, endothelium and nerves. These factors, together with a reported increased incidence of corneal infection, suggest that diabetic patients may be particularly susceptible to developing ocular complications during contact lens wear. Reports of contact lens-induced complications in diabetic patients do exist, although a number of these reports concern patients with advanced diabetic eye disease using lenses on an extended wear basis. Over the past decade or so, there have been published studies documenting the response of the diabetic eye to more modern contact lens modalities. The results of these studies suggest that contact lenses can be a viable mode of refractive correction for diabetic patients. Furthermore, new research suggests that the measurement of tear glucose concentration could, in future, be used to monitor metabolic control non-invasively in diabetic patients. This could be carried out using contact lenses manufactured from hydrogel polymers embedded with glucose-sensing agents or nanoscale digital electronic technology. The purpose of this paper is to review the literature on the anterior ocular manifestations of diabetes, particularly that pertaining to contact lens wear.     

Nosocomial pseudomonas aeruginosa-associated keratitis in soft contact lens wearer

BACKGROUND: Pseudomonas aeruginosa is the most common cause of bacterial-associated keratitis in soft contact lens wearers, due to wrong use of soft contact lenses. Problems are often severe corneal ulcers and even corneal perforations. We report on a soft contact lens wearer with credibly correct use of soft contact lenses and nosocomial Pseudomonas aeruginosa-associated keratitis. CASE REPORT: A 33-year old woman suffered from corneal ulcer and corneal infiltration with beginning endophthalmitis 2 days after having used of new soft contact lenses. After systemic and local antibiosis and penetrating keratoplasty we could stop endophthalmitis before reaching the vitreous and retina. RESULTS: Histological and microbiological examinations showed a corneal ulcer with severe corneal infection due to Pseudomonas aeruginosa with resistance to mezlocillin and intermediale resistance to gentamicin. After therapy a stable situation with visual acuity of 20/60 was attained. CONCLUSIONS: Previous reports on Pseudomonas aeruginosa-associated keratitis in soft contact lens wearers demonstrate corneal problems due to extended or overnight wear or unsuccessful contact lens cleaning. We present a case of nosocomial corneal infection after soft contact lens wearing and nosocomial infection because of contact with a partner working in an intensive-care unit. Hygienic rules should be strictly followed by patients and staff using soft or hard contact lenses for visual correction or for therapeutic reasons.     

Three month study of changes in the cornea after computer-determined and conventionally-determined contact lens fitting

The conventional rigid-lens fitting method uses fluorescein to assess the tear layer beneath a trial lens on the corneal surface. A more advanced technique, which uses a computer program to determine the back surface specifications of a contact lens from a pre-set tear layer thickness, has been studied. No significant difference was found in terms of corneal physiological changes between the conventionally determined contact lenses and computer-determined contact lenses after a three-month wearing period. The results suggest that there is little difference in the two methods of fitting. However, the computer determined method was found to be more efficient in terms of chair time, and also can aid inexperienced rigid lens practitioners to select the appropriate lens back surface curves.     

The Max Schapero Memorial Award Lecture 2004: contact lenses on and in the cornea, what the eye needs.

PURPOSE: The aim of this study is to review the advances made in understanding the needs of the cornea and the way in which it responds to contact lens wear and corneal implants. METHODS: The review is based on personal knowledge and involvement of the author and colleagues from the 1970s to 2005. RESULTS: Development of silicone hydrogel contact lenses is presented as well as development of synthetic materials for implantation on the corneal surface (corneal onlay). CONCLUSIONS: The future of vision correction involves developing highly porous and biocompatible lens materials. For contact lenses, a better understanding of the effects of contact lens wear on the ocular surfaces, including the tear film, and development of lens materials with greater bacterial resistance are required. For those who require new solutions to permanent vision correction, corneal onlays (implantable contact lenses) are a minimally invasive and totally reversible procedure that can be removed or replaced as visual needs change over time.     

Decay-accelerating factor in tears of contact lens wearers and patients with contact lens-associated complications.

PURPOSE: Complement activation fragments have been detected in the anterior segment during 1) eye closure, 2) contact lens wear, and 3) in some contact lens-associated pathologies. The decay-accelerating factor (DAF), a membrane-associated complement regulatory protein that inhibits the central C3 amplification convertases of the cascade, is present on both the ocular surface and in tears. In this study, we measured levels of tear DAF in asymptomatic contact lens patients and in patients who presented with contact lens-associated complications. METHODS: Tears were collected from 55 patients using capillary pipettes. Subjects included normal non-contact lens wearing controls (N = 14), asymptomatic soft (N = 13) and rigid gas permeable (N = 5) wearers, and individuals with contact lens-induced acute red eye (CLARE) (N = 4), ulcerative keratitis (N = 3), giant papillary conjunctivitis (GPC) (N = 8), contact lens peripheral ulcers (N = 3), and infiltrative keratitis (N = 5). Levels of DAF were assessed using a two-site immunoradiometric assay using anti-DAF monoclonal antibodies. RESULTS: The mean concentration of DAF in normal controls was found to be 149+/-78 ng/ml, 117+/-59 ng/ml, and 111+/-86 ng/ml for noncontact lens patients, and asymptomatic soft and rigid gas permeable lens wearers, respectively. In the conditions of CLARE, infiltrative keratitis, and GPC, DAF concentrations were significantly reduced compared with normal noncontact lens controls. Compared with asymptomatic soft lens patients, the condition of infiltrative keratitis showed a significant reduction in tear DAF. CONCLUSIONS: This study documents a trend toward decreased levels of tear DAF in patients with the contact lens associated inflammatory conditions CLARE, GPC, and infiltrative keratitis. Tears of patients with infiltrates show the most significant reduction of tear DAF. The reductions may be associated with enhanced complement activation contributing to the pathogeneses of infiltrative keratitis and associated ocular surface diseases.     

Influence of rigid contact lens base curve radius on tear pump efficiency.

The effects of rigid contact lens base curve radius changes on tear pump efficiency were determined by measuring oxygen uptake on six with-the-rule corneas (with toricities between 0.37 and 1.00 D) under three conditions: (1) normal open eye, (2) after 5 min of static (without blinking) wear of polymethyl methacrylate (non-gas permeable) contact lenses, and (3) after 5 min of dynamic (with blinking once every 5 s) wear of the same lenses. The difference between the oxygen uptake rates measured under static and dynamic conditions provides an index of tear pump efficiency. Each subject wore a series of five lenses: fitted on K and 0.05 or 0.10 mm steeper and flatter than the flattest corneal meridian. The overall diameter of all lenses was 8.8 mm, the optic zone was 7.4 mm, the axial edge lift was 0.09 mm, and all other parameters were constant. The contact lens fitted on K was associated with the greatest central corneal oxygen debt under static conditions, whereas the same lens also provided for the best tear exchange with the blink. In addition, better tear exchange was found to be associated with larger palpebral aperture sizes.     

Contact lens induced keratitis associated with contact lens wear

PURPOSE: To evaluate clinical characteristics, risk factors, management and outcome of contact lens induced keratitis (CLIK) associated with contact lens wear. METHODS: The study comprised all consecutive patients presenting with contact lens related presumed microbial keratitis during a 12-month period at our department. Detailed demographic data, type of contact lens, duration of lens wear, wearing schedule and lens hygiene were derived from a self-administered questionnaire. Severity of ulcer, corneal scrapings, treatment and final outcome were evaluated. RESULTS: 27 patients with CLIK, some of which may have been sterile peripheral infiltrates, due to contact lens wear were detected. In the majority of the cases patients had used disposable soft contact lenses (89%) and most of them had a daily wearing schedule (78%). 51.8% patients cleaned their lenses regularly. 6 (22%) applied no disinfection since their lenses were disposable on removal. In 3 of our cases with CLIK, penetrating keratoplasty had to be performed. CONCLUSION: Disposable contact lenses seem to have been a predisposing factor for contact lens induced keratitis also when used on a daily wear schedule. Insufficient contact lens care products and/or manufacturing characteristics may be responsible for CLIK, which is also observed in otherwise compliant contact lens users. In 3 of our patients with CLIK keratoplasty became necessary, indicating that contact lens induced keratitis may result in severe corneal complications.     

The contribution of bacterial surface hydrophobicity to the process of adherence of Pseudomonas aeruginosa to hydrophilic contact lenses

Ten isolates of Pseudomonas aeruginosa obtained from the corneas of patients with Pseudomonas keratitis adhered to soft contact lenses in significantly greater numbers than did six isolates from other body sites (P less than .05). However, there was no predominant serotype among the 10 corneal isolates tested. Isolates grown statically in broth at 37 degrees C formed a pellicle and adhered two times as much to contact lenses as did isolates grown in broth while shaking which did not form a pellicle (P less than .01). The more adherent isolates (grown at 37 degrees C) were shown to be more hydrophobic than the less adherent bacteria (grown at 26 degrees C) by their propensity to accumulate at the interface between hexadecane and saline and their movement into polyethylene glycol from dextran. These corneal isolates agglutinated erythrocytes, a process that was inhibited by dilute solutions (as low as 0.01%) of three commonly used surfactants. These same surfactants inhibited the adherence of Pseudomonas aeruginosa to soft contact lens surfaces by as much as 52%. It is concluded that hydrophobic interactions may significantly contribute to the ability of Pseudomonas aeruginosa to adhere to contact lenses.     

The effects of six months of contact lens wear on the tear film, ocular surfaces, and symptoms of presbyopes.

PURPOSE: To assess the tear film, ocular surfaces, and symptoms of ocular discomfort in a presbyopic population before and after contact lens wear. METHODS: A total of 150 presbyopes (49% were previous soft contact lens wearers) participated in a clinical trial in which they wore either monovision (single vision Acuvue lenses) or Acuvue Bifocal contact lenses. Clinical measurements of tear film, biomicroscopy, and corneal sensitivity as well as subjective ratings using the Dry Eye Questionnaire were collected at the initial visit and repeated after 6 months. Comparisons were made between age groups (40 to 51 years and 52 to 71 years) and genders before and after contact lens wear. Associations between objective and subjective tests were sought. RESULTS: After 6 months of contact lens wear, clinical signs had worsened by less than one-half of a grade, and tear break up time (TBUT) worsened by 3 s. Only TBUT was lower for the older age group. Females had less bulbar hyperemia, more sensitive eyes, more lissamine green staining, and lower TBUT and phenol red thread measurements (all p < 0.04). Twenty-eight percent experienced dryness before contact lens wear, but this figure increased to 68% when wearing contact lenses. There were no age differences, but almost twice as many females as males reported dryness. Reporting symptoms of dryness was associated with gender, corneal sensitivity, and type of corneal staining. CONCLUSIONS: These results provide a representation of the ocular surface condition and symptoms of ocular discomfort in the middle-aged population and seem similar to reports of younger populations. Wearing contact lenses seems to influence dry eye symptoms more than age or gender. Therefore, presbyopes should not be excluded from consideration for contact lens fitting.     

Silicone hydrogel contact lenses and the ocular surface

For 30 years, contact lens research focused on the need for highly oxygen-permeable (Dk) soft lens materials. High Dk silicone hydrogel contact lenses, made available in 1999, met this need. The purpose of this review is to examine how silicone hydrogel lens wear affects the ocular surfaces and to highlight areas in which further research is needed to improve biocompatibility. Silicone hydrogel lenses have eliminated lens-induced hypoxia for the majority of wearers and have a less pronounced effect on corneal homeostasis compared to other lens types; however, mechanical interaction with ocular tissue and the effects on tear film structure and physiology are similar to that found with soft lens wear in general. Although the ocular health benefits of silicone hydrogel lenses have increased the length of time lenses can be worn overnight, the risk of infection is similar to that found with other soft lens types, and overnight wear remains a higher risk factor for infection than daily wear, regardless of lens material. Future contact lens research will focus on gaining a better understanding of the way in which contact lenses interact with the corneal surface, upper eyelid, and the tear film, and the lens-related factors contributing to infection and inflammatory responses.