Factors affecting Staphylococcus epidermidis adhesion to contact lenses

Biology and Regulation of Staphylococcal Biofilm

Despite continuing progress in medical and surgical procedures, staphylococci remain the major Gram-positive bacterial pathogens that cause a wide spectrum of diseases, especially in patients requiring the utilization of indwelling catheters and prosthetic devices implanted temporarily or for prolonged periods of time. Within the genus, if Staphylococcus aureus and S. epidermidis are prevalent species responsible for infections, several coagulase-negative species which are normal components of our microflora also constitute opportunistic pathogens that are able to infect patients. In such a clinical context, staphylococci producing biofilms show an increased resistance to antimicrobials and host immune defenses. Although the biochemical composition of the biofilm matrix has been extensively studied, the regulation of biofilm formation and the factors contributing to its stability and release are currently still being discovered. This review presents and discusses the composition and some regulation elements of biofilm development and describes its clinical importance. Finally, we summarize the numerous and various recent studies that address attempts to destroy an already-formed biofilm within the clinical context as a potential therapeutic strategy to avoid the removal of infected implant material, a critical event for patient convenience and health care costs.

Microbial Adherence to Contact Lenses and Pseudomonas aeruginosa as a Model Organism for Microbial Keratitis

Microbial keratitis (MK), the infection of the cornea, is a devastating disease and the fifth leading cause of blindness and visual impairment around the world. The overwhelming majority of MK cases are linked to contact lens wear combined with factors which promote infection such as corneal abrasion, an immunocompromised state, improper contact lens use, or failing to routinely disinfect lenses after wear. Contact lens-related MK involves the adherence of microorganisms to the contact lens. Therefore, this review discusses the information currently available regarding the disease pathophysiology, the common types of microorganisms causing MK, physical and organic mechanisms of adhesion, material properties which are involved in adhesion, and current antimicrobial strategies. This review also concludes that Pseudomonas aeruginosa is a model organism for the investigation of contact lens microbial adherence due to its prevalence in MK cases, its extremely robust adhesion, antimicrobial-resistant properties, and the severity of the disease it causes.

Correlation of Staphylococcus Epidermidis Phenotype and Its Corneal Virulence

PURPOSE

S. epidermidis is an ocular pathogen and a leading cause of keratitis. It produces hemolysins and at least 3 proteases. The purpose of the present study is to compare the secretion of hemolysins and proteases between 28 ocular isolates and one non-ocular strain and to determine their relationship to ocular virulence in selected strains using a rabbit model of infection.

MATERIALS AND METHODS

Culture supernatants were compared for protease production and hemolysis. Selected strains were injected into rabbit corneas and their virulence and pathology recorded. The major protease activity in a virulent strain was identified and the gene was cloned and expressed as a recombinant protein. The corneal toxicity of this protease was determined. Antibodies to the native protease were generated and tested for neutralizing activity in vivo and in vitro. The corneal pathology of the S. epidermidis protease was compared to the pathology of S. aureus V8 protease.

RESULTS

Strains that exhibited the least protease activity in vitro caused significantly less ocular pathology in vivo (p ≤ 0.003). Strains that were hemolytic and secreted a major protease had numerically higher SLE scores. This protease was identified as the serine protease Esp. The recombinant Esp protease caused extensive pathology when injected into the corneal stroma (7.62 ± 0.33). Antibody generated against native Esp did not neutralize the activity of the protease in vivo or in vitro. The antibody reacted with Esp proteases secreted by other S. epidermidis strains. S. epidermidis Esp protease and its homologue in S. aureus caused similar ocular pathology when injected in the rabbit corneal stroma.

CONCLUSION

Hemolysins and proteases seem to be important in corneal pathology caused by S. epidermidis infections. The Esp protease mediates significant corneal damage. S. epidermidis Esp and S. aureus V8 protease caused similar and extensive edema in rabbit corneas.

Contact lens-related corneal infection: Intrinsic resistance and its compromise

Contact lenses represent a widely utilized form of vision correction with more than 140 million wearers worldwide. Although generally well-tolerated, contact lenses can cause corneal infection (microbial keratitis), with an approximate annualized incidence ranging from ~2 to ~20 cases per 10,000 wearers, and sometimes resulting in permanent vision loss. Research suggests that the pathogenesis of contact lens-associated microbial keratitis is complex and multifactorial, likely requiring multiple conspiring factors that compromise the intrinsic resistance of a healthy cornea to infection. Here, we outline our perspective of the mechanisms by which contact lens wear sometimes renders the cornea susceptible to infection, focusing primarily on our own research efforts during the past three decades. This has included studies of host factors underlying the constitutive barrier function of the healthy cornea, its response to bacterial challenge when intrinsic resistance is not compromised, pathogen virulence mechanisms, and the effects of contact lens wear that alter the outcome of host-microbe interactions. For almost all of this work, we have utilized the bacterium Pseudomonas aeruginosa because it is the leading cause of lens-related microbial keratitis. While not yet common among corneal isolates, clinical isolates of P. aeruginosa have emerged that are resistant to virtually all currently available antibiotics, leading the United States CDC (Centers for Disease Control) to add P. aeruginosa to its list of most serious threats. Compounding this concern, the development of advanced contact lenses for biosensing and augmented reality, together with the escalating incidence of myopia, could portent an epidemic of vision-threatening corneal infections in the future. Thankfully, technological advances in genomics, proteomics, metabolomics and imaging combined with emerging models of contact lens-associated P. aeruginosa infection hold promise for solving the problem - and possibly life-threatening infections impacting other tissues.

Acute Onset of Exogenous Endophthalmitis after Dexamethasone Implant Injection Treated without Implant Removal

We present a case of acute endophthalmitis after intravitreal dexamethasone implant injection and discuss the management of this rare and challenging case in which the implant could not be removed. A 50-year-old woman with a history of branch retinal vein occlusion in the right eye was treated with intravitreal dexamethasone implant injection for macular oedema. Four days after injection, the patient was admitted to the department with acute pain, decreased vision, and redness. A diagnosis of acute post-intravitreal injection endophthalmitis was made. A 23-guage (23G) vitrectomy was performed immediately to remove the implant, and a vitreous tap for culture and polymerase chain reaction was acquired during the procedure. We were unable to remove the dexamethasone implant during the vitrectomy because of dense membrane formation. At the end of the procedure, we injected intravitreal antibiotics (vancomycin and amikacin), and the patient was treated with fortified topical antibiotics and steroids. At the time of writing, 5 years later, the patient retains a best corrected visual acuity of 10/10 (6/6) with dexamethasone implant therapy maintenance. Intravitreal dexamethasone implant-associated endophthalmitis is a rare and challenging condition. Immediate 23G pars plana vitrectomy, even without removal of the implant, can lead to favourable visual results.

Microbial keratitis: could contact lens material affect disease pathogenesis?

Microbial keratitis is a sight-threatening complication associated with contact lenses. The introduction of silicone hydrogel lens materials with increased oxygen transmission to the ocular surface has not significantly altered the incidence of microbial keratitis. These data suggest that alternate, or additional, predisposing factors involving lens wear must be addressed to reduce or eliminate these infections. The contact lens can provide a surface for microbial growth in situ and can also influence ocular surface homeostasis through effects on the tear fluid and corneal epithelium. Thus, it is intuitive that future contact lens materials could make a significant contribution to preventing microbial keratitis. Design of the "right" material to prevent microbial keratitis requires understanding the effects of current materials on bacterial virulence in the cornea and on ocular surface innate defenses. Current knowledge in each of these areas will be presented with a discussion of future directions needed to understand the influence of lens material on the pathogenesis of microbial keratitis.

Colonization of hydrophilic contact lenses by yeast

The growth of six strains of yeast was analyzed in vitro in order to assess their capacity for colonizing (adhesion and invasion) hydrophilic contact lenses. Lenses with different water content were cultured in two culture media for 3, 7, 14, and 21 days. Only strain 93150 of Candida albicans could adhere to and invade the polymers. Specifically, fungal growth was observed in cultures with Sabouraud's broth. The degree of yeast colonization of contact lenses was significantly related to the species, the strain, and the culture medium in which the yeast and lenses were cultured. The results here obtained were compared with those reported for the filamentous fungus Aspergillus niger 2700. For both microorganisms, the strain and the medium in which the lenses and microorganism were cultured influenced the colonization, but the percentage of colonized lenses, the degree of colonization, and the density and size of the internalized colonies were always noticeably lower for C. albicans 93150. Colonization by A. niger 2700 was also related to the type of material of the lenses and the incubation period. For both microorganisms, when the strain is right and the growth and development are correct, colonization of hydrophilic contact lenses occurs.

Adherence of two strains of Staphylococcus epidermidis to contact lenses

PURPOSE

To compare the adherence of biofilm-producer and nonbiofilm-producer Staphylococcus epidermidis in vitro to different soft contact lenses (CLs) to study its possible contribution to the pathogenesis of keratitis.

METHODS

Strains of S. epidermidis slime-positive ATCC 35984 (biofilm-producer) and slime-negative ATCC 12228 (nonbiofilm-producer) were used with eight types of soft CLs from the four groups determined by the United States Food and Drug Administration (FDA), according to the ionicity and water content. The lenses were incubated overnight with the bacteria, then sonicated and vortexed to separate the adhered bacteria. Quantitative cultures were performed and the results statistically analyzed.

RESULTS

Slime-negative strains of S. epidermidis were able to adhere to all CLs but at a lower level than slime-positive strains. There were significant differences in bacterial attachment among the four FDA groups. On the whole, there was higher bacterial adhesion to nonionic and low-water content materials. Contact lenses produced by soft molding were less adherent than CLs produced by either lathe-cutting or spin-casting.

CONCLUSIONS

Bacterial biofilm favors bacterial adhesiveness and colonization of soft CLs. Bacterial attachment was less in soft molding CLs (etafilcon A), which provide a more homogeneous and smoother surface.

Bacterial interactions with contact lenses; effects of lens material, lens wear and microbial physiology

Contact lens wear is a successful form of vision correction. However, adverse responses can occur during wear. Many of these adverse responses are produced as a consequence of bacterial colonization of the lens. The present study demonstrated that during asymptomatic contact lens wear lenses are colonized by low levels of bacteria with gram-positive bacteria, such as coagulase negative staphylococci, predominating. Gram-negative bacteria are frequently the causative agents of adverse responses during contact lens wear. Measuring the adhesion of different strains and/or species of bacteria to different contact lens materials demonstrated considerable differences. In particular. Pseudormonas aeruginosa strains Paerl and 6294 and Aeromonas hydrophilia strain Ahyd003 adhered in larger numbers to the highly oxygen permeable contact lenses Balafilcon A compared to hydrogel lenses manufactured from either Etafilcon A or HEMA. Furthermore, after Balafilcon A lenses had been worn for 6 h during the day bacteria were able to adhere in greater numbers to the worn lenses compared to the unworn lenses with increases in adhesion ranging from 243% to 1393%. However, wearing Etafilcon A lenses usually resulted in a decrease in adhesion (22-48%). Bacteria were able to grow after adhesion to lenses soaked in artificial tear fluid and formed biofilms, visualized by scanning confocal microscopy. Chemostat grown bacterial cultures were utilized to enable control of bacterial growth conditions and bacteria were shown to adhere in the greatest numbers if grown under low temperature (25 degrees C compared to 37 degrees C). The changes in growth temperature was shown. using 2D gel electrophoresis, to change the experssion of cell-surface proteins and, using ID gel electrophoresis, to change the expression of surface lipopolysaccharide of P. aeruginosa Paerl. Thus, these surface changes would have been likely to have mediated the increased adhesion to Etafilcon A contact lenses.

The collagen-binding adhesin is a virulence factor in Staphylococcus aureus keratitis

A collagen-binding strain of Staphylococcus aureus produced suppurative inflammation in a rabbit model of soft contact lens-associated bacterial keratitis more often than its collagen-binding-negative isogenic mutant. Reintroduction of the cna gene on a multicopy plasmid into the mutant helped it regain its corneal adherence and infectivity. The topical application of a collagen-binding peptide before bacterial challenge decreased S. aureus adherence to deepithelialized corneas. These data suggest that the collagen-binding adhesin is involved in the pathogenesis of S. aureus infection of the cornea.