Factors impacting corneal epithelial barrier function against Pseudomonas aeruginosa traversal

In vitro and ex vivo models of microbial keratitis: Present and future

Microbial keratitis (MK) is an infection of the cornea, caused by bacteria, fungi, parasites, or viruses. MK leads to significant morbidity, being the fifth leading cause of blindness worldwide. There is an urgent requirement to better understand pathogenesis in order to develop novel diagnostic and therapeutic approaches to improve patient outcomes. Many in vitro, ex vivo and in vivo MK models have been developed and implemented to meet this aim. Here, we present current in vitro and ex vivo MK model systems, examining their varied design, outputs, reporting standards, and strengths and limitations. Major limitations include their relative simplicity and the perceived inability to study the immune response in these MK models, an aspect widely accepted to play a significant role in MK pathogenesis. Consequently, there remains a dependence on in vivo models to study this aspect of MK. However, looking to the future, we draw from the broader field of corneal disease modelling, which utilises, for example, three-dimensional co-culture models and dynamic environments observed in bioreactors and organ-on-a-chip scenarios. These remain unexplored in MK research, but incorporation of these approaches will offer further advances in the field of MK corneal modelling, in particular with the focus of incorporation of immune components which we anticipate will better recapitulate pathogenesis and yield novel findings, therefore contributing to the enhancement of MK outcomes.

A Novel Technique for Corneal Transepithelial Electrical Resistance Measurement in Mice

We developed a technique that can measure corneal transepithelial electrical resistance (TER) in mice, which was used for evaluating corneal toxicity induced by ophthalmic drugs. We used a tissue culture well and its insert to mount the mouse globe and separated the cornea from the rest of the globe to enable corneal TER measurements to be taken. The explanted mouse eyes were divided into groups, and the corneal epithelia were exposed to different concentrations of BAC. Half of these eyes were fixed for transmission electron microscopy (TEM) examination and the other for ZO-1 immunohistochemical (IHC) evaluation. After exposure to control, 0.1%, 0.2%, and 0.5% BAC, the TER was 100 ± 0%, 91 ± 14%, 83 ± 13%, and 34 ± 12% of the pre-exposure TER at 1 min, respectively, with a statistically significant decrease in the 0.5% group. After 3 min, the TER showed a statistically significant decrease in the 0.2% and 0.5% groups. The TEM examinations showed a loss of epithelial tight junctions between superficial cells in the 0.2% and 0.5% groups. The IHC examination showed decreased ZO-1 staining of the corneal epithelium of the same groups as compared to the control. To the best of our knowledge, we succeeded in developing an innovative technique for corneal TER measurement in mice.

Evaluating and Managing the Microbial Contamination of Eye Drops: A Two-Phase Hospital-Based Study

The microbial contamination of eye drop tips and caps varies between 7.7% and 100%. In seeking patient protection and continuous improvement, the Pharmacy Department in the Sterile Ophthalmological and Oncological Preparations Unit at Cochin Hospital AP-HP, Paris, France, conducted a two-phase study to compare the antimicrobial efficiency and practical use of standard packaging and a marketed eye drop container incorporating a self-decontaminating antimicrobial green technology by Pylote SAS at the tip and cap sites. The first phase was conducted in situ to identify the microbial contaminants of eye drops used in the hospital and community settings. A total of 110 eye drops were included for testing. Staphylococcus species were the most prevalent bacteria. Candida parapsilosis was detected in only one residual content sample and, at the same time, on the cap and tip. The second phase was performed in vitro, according to JIS Z2801. Reductions above one log in Staphylococcus aureus and Pseudomonas aeruginosa counts were noted in Pylote SAS eye drop packaging after 24 h of contact. The practical tests showed satisfactory results. Pylote SAS antimicrobial mineral oxide technology exhibited promising effects that combined effectiveness, safety, and sustainability to protect the patient by preventing infections due to the contamination of eye drop containers.

Restoration of corneal epithelial barrier function: A possible target for corneal neovascularization

Corneal neovascularization (CoNV) is the second leading common cause of vision impairment worldwide and is a blinding pathological alteration brought on by ocular trauma, infection, and other factors. There are some limitations in the treatment of CoNV, hence it's critical to look into novel therapeutic targets. The corneal epithelial barrier, which is the initial barrier of the ocular surface, is an important structure that shields the eye from changes in the internal environment or invasion by the external environment. This study sought to collate evidence on the regulation of corneal epithelial barrier injury on the activation of vascular endothelial cells (VECs), basement membrane (BM) degradation, differentiation, migration, and proliferation of VECs, vascular maturation and stability, and other key processes in CoNV, so as to provide a novel concept for CoNV therapy targeting corneal epithelial barrier repair.

Bone morphogenetic protein 4 thermosensitive hydrogel inhibits corneal neovascularization by repairing corneal epithelial apical junctional complexes

Corneal neovascularization (CNV) is a heavy attribute of blinding disease changes. Existing medications need numerous infusions and have a limited absorption. Investigating novel drugs with safety, efficacy, and convenience is crucial. In this study, we developed a bone morphogenetic protein 4 (BMP4)-loaded poloxamer-oxidized sodium alginate (F127-OSA) thermosensitive hydrogel. The 14 % F127-OSA hydrogel transformed from sol to gel at 31-32 °C, which might extend the application period on the ocular surface. The hydrogel's porous structure and uniform dispersion made it possible for drugs to release gradually. We used a suture-induced rat CNV model to investigate the mechanism of CNV inhibition by hydrogel. We discovered that F127-OSA hydrogel loaded with BMP4 could significantly reduce the length and area of CNV, relieve corneal edema, and stop aberrant epithelial cell proliferation. The hydrogel's efficacy was superior to that of the common solvent group. Additionally, BMP4 thermosensitive hydrogel repaired ultrastructure, including microvilli, intercellular junctions, and damaged apical junctional complexes (AJCs), suggesting a potential mechanism by which the hydrogel prevented CNV formation. In conclusion, our investigation demonstrates that F127-OSA thermosensitive hydrogel loaded with BMP4 can repair corneal epithelial AJCs and is a promising novel medication for the treatment of CNV.

Molecular nature of ocular surface barrier function, diseases that affect it, and its relevance for ocular drug delivery

The structural and functional integrity of the ocular surface, a continuous epithelial structure comprised of the cornea, the conjunctiva, and the ductal surface of the lacrimal as well as meibomian glands, is crucial for proper vision. The ocular surface barrier function (OSBF), sum of the different types of protective mechanisms that exist at the ocular surface, is essential to protect the rest of the eye from vision-threatening physical, chemical, and biological insults. OSBF helps maintain the immune privileged nature of the cornea and the aqueous humor by preventing entry of infectious agents, allergens, and noxious chemicals. Disruption of OSBF exposes the dense nerve endings of the cornea to these stimuli, resulting in discomfort and pain. This review summarizes the status of our knowledge related to the molecular nature of OSBF, describes the effect of different ocular surface disorders on OSBF, and examines the relevance of this knowledge for ocular drug delivery.

Comparative Evaluation of Pseudomonas aeruginosa Adhesion to a Poly-(2-Methacryloyloxyethyl Phosphorylcholine)-Modified Silicone Hydrogel Contact Lens

Pseudomonas aeruginosa is the most common causative agent associated with microbial keratitis. During contact lens wear, pathogens may be introduced into the ocular environment, which might cause adverse events. Lehfilcon A is a recently developed contact lens with a water gradient surface composed of polymeric 2-methacryloyloxyethyl phosphorylcholine (MPC). MPC is re-ported to impart anti-biofouling properties onto modified substrates. Therefore, in this in vitro experimental study, we tested the capability of lehfilcon A to resist adhesion by P. aeruginosa. Quantitative bacterial adhesion assays using five strains of P. aeruginosa were conducted to compare the adherence properties of lehfilcon A to five currently marketed silicone hydrogel (SiHy) contact lenses (comfilcon A, fanfilcon A, senofilcon A, senofilcon C, and samfilcon A). Compared to lehfilcon A, we observed 26.7 ± 8.8 times (p = 0.0028) more P. aeruginosa binding to comfilcon A, 30.0 ± 10.8 times (p = 0.0038) more binding to fanfilcon A, 18.2 ± 6.2 times (p = 0.0034) more binding to senofilcon A, 13.6 ± 3.9 times (p = 0.0019) more binding to senofilcon C, and 29.5 ± 11.8 times (p = 0.0057) more binding to samfilcon A. These results demonstrate that, for various strains of P. aeruginosa, lehfilcon A reduces bacterial adhesion compared to other contact lens materials.

Impact of High Glucose on Ocular Surface Glycocalyx Components: Implications for Diabetes-Associated Ocular Surface Damage

Diabetes mellitus causes several detrimental effects on the ocular surface, including compromised barrier function and an increased risk of infections. The glycocalyx plays a vital role in barrier function. The present study was designed to test the effect of a high glucose level on components of glycocalyx. Stratified human corneal and conjunctival epithelial cells were exposed to a high glucose concentration for 24 and 72 h. Changes in Mucin (MUC) 1, 4, 16 expression were quantified using real-time PCR and ELISA. Rose bengal and jacalin staining were used to assess the spatial distribution of MUC16 and O-glycosylation. Changes in the gene expression of five glycosyltransferases and forty-two proteins involved in cell proliferation and the cell cycle were also quantified using PCR and a gene array. High glucose exposure did not affect the level or spatial distribution of membrane-tethered MUC 1, 4, and 16 either in the corneal or conjunctival epithelial cells. No change in gene expression in glycosyltransferases was observed, but a decrease in the gene expression of proteins involved in cell proliferation and the cell cycle was observed. A high-glucose-mediated decrease in gene expression of proteins involved in cellular proliferation of corneal and conjunctival epithelial cells may be one of the mechanisms underlying a diabetes-associated decrease in ocular surface's glycocalyx.

Highlighting the Microbial Contamination of the Dropper Tip and Cap of In-Use Eye Drops, the Associated Contributory Factors, and the Risk of Infection: A Past-30-Years Literature Review

The sterility of eye drop content is a primary concern from manufacturing until opening, as well as during handling by end users, while microbial contamination of the dropper tip and cap are often disregarded. The contamination of these sites during drug administration represents a risk of microbial transmission and ocular infection. In this review, we aim to assess microbial contamination of the dropper tip and cap of in-use eye drops, the associated contributory factors, and the risk of infection. We conducted a literature search of the MEDLINE, PubMed, and Cochrane Central databases. A total of 31 out of 1503 studies were selected. All the studies conducted in different settings that documented microbiologically contaminated in-use eye drops were included. Our review showed that microbial contamination of the dropper tip and cap of in-use eye drops ranged from 7.7 to 100% of the total contaminated tested samples. Documented contributory factors were conflicting across the literature. Studies investigating the association between eye infection and microbial contamination of the dropper tip and cap were scarce. New technologies offer a promising potential for securing the long-term sterility of eye drop content, tips, and caps, which could benefit from more research and well-defined study protocols under real-life scenarios.

Role of surfactant protein-D in ocular bacterial infection

Purpose

Our review explains the role of surfactant protein D (SP-D) in different kinds of bacterial infection based on its presence in different ocular surface tissues. We discuss the potential role of SP-D against invasion by pathogens, with the aim of identifying new prospects for the possible mechanism of SP-D-mediated immune processes, and the diagnosis, prognosis, or treatment of ocular bacterial infection.

Methods

We reviewed articles about the role of SP-D in various ocular bacterial infections or infection-related ocular diseases through PubMed, Google Scholar, and the Web of Science databases.

Results

SP-D acts as an important immune factor that can resemble molecules in different polymerization states and that defends against pathogen invasion. The increased SP-D production and secretion in tear fluid and the cornea after ocular bacterial infections such as Staphylococcus aureus, Pseudomonas aeruginosa keratitis, and infection-related ocular diseases, was shown to have potential anti-inflammatory effects. The mechanisms of SP-D’s action against ocular bacterial infections include presenting, aggregating, opsonizing, and phagocytizing antigens, as well as regulating anti-bacterial immunity processes, including toll-like receptor-5 (TLR-5) pathway and IL-8 effect, TLR-4 and TLR-2 pathways and other possible ways remained to be elucidated in more detail. The findings demonstrate the potential of SP-D as an important clinical diagnostic biomarker prognosis predictor, and target for ocular immunotherapy.

Conclusion

SP-D participates in invasion by different ocular bacteria and infection-related ocular diseases through multiple immune mechanisms. This finding provides new prospects for the diagnosis, prognosis and treatment of ocular bacterial infection.

Mammals' humoral immune proteins and peptides targeting the bacterial envelope: from natural protection to therapeutic applications against multidrug‐resistant Gram ‐negatives

Mammalian innate immunity employs several humoral ‘weapons’ that target the bacterial envelope. The threats posed by the multidrug‐resistant ‘ESKAPE’ Gram‐negative pathogens (Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) are forcing researchers to explore new therapeutic options, including the use of these immune elements. Here we review bacterial envelope‐targeting (peptidoglycan and/or membrane‐targeting) proteins/peptides of the mammalian immune system that are most likely to have therapeutic applications. Firstly we discuss their general features and protective activity against ESKAPE Gram‐negatives in the host. We then gather, integrate, and discuss recent research on experimental therapeutics harnessing their bactericidal power, based on their exogenous administration and also on the discovery of bacterial and/or host targets that improve the performance of this endogenous immunity, as a novel therapeutic concept. We identify weak points and knowledge gaps in current research in this field and suggest areas for future work to obtain successful envelope‐targeting therapeutic options to tackle the challenge of antimicrobial resistance.

Nerve-associated transient receptor potential ion channels can contribute to intrinsic resistance to bacterial adhesion in vivo

The cornea of the eye differs from other mucosal surfaces in that it lacks a viable bacterial microbiome and by its unusually high density of sensory nerve endings. Here, we explored the role of corneal nerves in preventing bacterial adhesion. Pharmacological and genetic methods were used to inhibit the function of corneal sensory nerves or their associated transient receptor potential cation channels TRPA1 and TRPV1. Impacts on bacterial adhesion, resident immune cells, and epithelial integrity were examined using fluorescent labeling and quantitative confocal imaging. TRPA1/TRPV1 double gene-knockout mice were more susceptible to adhesion of environmental bacteria and to that of deliberately-inoculated Pseudomonas aeruginosa. Supporting the involvement of TRPA1/TRPV1-expressing corneal nerves, P. aeruginosa adhesion was also promoted by treatment with bupivacaine, or ablation of TRPA1/TRPV1-expressing nerves using RTX. Moreover, TRPA1/TRPV1-dependent defense was abolished by enucleation which severs corneal nerves. High-resolution imaging showed normal corneal ultrastructure and surface-labeling by wheat-germ agglutinin for TRPA1/TRPV1 knockout murine corneas, and intact barrier function by absence of fluorescein staining. P. aeruginosa adhering to corneas after perturbation of nerve or TRPA1/TRPV1 function failed to penetrate the surface. Single gene-knockout mice showed roles for both TRPA1 and TRPV1, with TRPA1^-/- more susceptible to P. aeruginosa adhesion while TRPV1^-/- corneas instead accumulated environmental bacteria. Corneal CD45+/CD11c+ cell responses to P. aeruginosa challenge, previously shown to counter bacterial adhesion, also depended on TRPA1/TRPV1 and sensory nerves. Together, these results demonstrate roles for corneal nerves and TRPA1/TRPV1 in corneal resistance to bacterial adhesion in vivo and suggest that the mechanisms involve resident immune cell populations.

Foundational concepts in the biology of bacterial keratitis

Bacterial infections of the cornea, or bacterial keratitis (BK), are notorious for causing rapidly fulminant disease and permanent vision loss, even among treated patients. In the last sixty years, dramatic upward trajectories in the frequency of BK have been observed internationally, driven in large part by the commercialization of hydrogel contact lenses in the late 1960s. Despite this worsening burden of disease, current evidence-based therapies for BK - including broad-spectrum topical antibiotics and, if indicated, topical corticosteroids - fail to salvage vision in a substantial proportion of affected patients. Amid growing concerns of rapidly diminishing antibiotic utility, there has been renewed interest in urgently needed novel treatments that may improve clinical outcomes on an individual and public health level. Bridging the translational gap in the care of BK requires the identification of new therapeutic targets and rational treatment design, but neither of these aims can be achieved without understanding the complex biological processes that determine how bacterial corneal infections arise, progress, and resolve. In this chapter, we synthesize the current wealth of human and animal experimental data that now inform our understanding of basic BK pathophysiology, in context with modern concepts in ocular immunology and microbiology. By identifying the key molecular determinants of clinical disease, we explore how novel treatments can be developed and translated into routine patient care.

The Role of Elastase in Corneal Epithelial Barrier Dysfunction Caused by Pseudomonas aeruginosa Exoproteins

Purpose

To investigate the role of elastase in corneal epithelial barrier dysfunction caused by the exoproteins secreted by Pseudomonas aeruginosa.

Methods

Exoproteins obtained from Pseudomonas aeruginosa culture supernatant were analyzed by shotgun proteomics approach. In vitro multilayered rabbit corneal epithelial barrier model prepared by air-liquid interface technique (CECs-ALI) were treated with 2 µg/ml exoproteins and/or 8 mM elastase inhibitor. Then the epithelial barrier function was evaluated by transepithelial electrical resistance (TEER) assay and tight junction proteins immunofluorescence. Cell viability and the apoptosis rate were examined by CCK8 assay and flow cytometry. TNF-α, IL-6, IL-8, and IL-1β levels were measured by ELISA. Mice cornea treated with exoproteins and/or elastase inhibitor were evaluated in vivo and in vitro.

Results

Elastase (24.2%) is one of the major components of exoproteins. After 2 µg/ml exoproteins were applied to CECs-ALI for two hours, TEER decreased from 323.2 ±  2.7 to 104 ± 6.8 Ω/cm² (P < 0.001). The immunofluorescence results showed a distinct separation in tight junction and significant degradation of ZO-1 and occludin (P < 0.05). Elastase inhibitor (8 mM) alleviated the decrease in TEER value (234 ± 6.8 Ω cm²) induced by exoproteins. Inhibition of elastase decreased the apoptosis rate of CECs treated with exoproteins from 30.2 ± 3.8% to 7.26 ± 1.3% and the levels of inflammatory factors (P < 0.05). Mice corneal epithelium defect could be induced by exoproteins and protected by elastase inhibitor.

Conclusions

Elastase plays a critical role in corneal epithelial barrier dysfunction caused by Pseudomonas aeruginosa exoproteins via damaging tight junctions. The inhibition of elastase could protect the corneal epithelial barrier via reducing virulence and inflammation.

Pseudomonas aeruginosa-induced nociceptor activation increases susceptibility to infection

We report a rapid reduction in blink reflexes during in vivo ocular Pseudomonas aeruginosa infection, which is commonly attributed and indicative of functional neuronal damage. Sensory neurons derived in vitro from trigeminal ganglia (TG) were able to directly respond to P. aeruginosa but reacted significantly less to strains of P. aeruginosa that lacked virulence factors such as pili, flagella, or a type III secretion system. These observations led us to explore the impact of neurons on the host's susceptibility to P. aeruginosa keratitis. Mice were treated with Resiniferatoxin (RTX), a potent activator of Transient Receptor Potential Vanilloid 1 (TRPV1) channels, which significantly ablated corneal sensory neurons, exhibited delayed disease progression that was exemplified with decreased bacterial corneal burdens and altered neutrophil trafficking. Sensitization to disease was due to the increased frequencies of CGRP-induced ICAM-1+ neutrophils in the infected corneas and reduced neutrophil bactericidal activities. These data showed that sensory neurons regulate corneal neutrophil responses in a tissue-specific matter affecting disease progression during P. aeruginosa keratitis. Hence, therapeutic modalities that control nociception could beneficially impact anti-infective therapy.

Knockdown of IQGAP-1 Enhances Tight Junctions and Prevents P. aeruginosa Invasion of Human Corneal Epithelial Cells

PURPOSE

To determine the role of IQ-domain GTPase-activating protein1 (IQGAP-1) in tight junctions of human corneal epithelial cells (HCECs) and its effect against P. aeruginosa (PAK) invasion.

MATERIAL AND METHODS

Primary human corneal epithelial cells (HCECs), immortalized HCECs, and IQGAP-1 RNA knockdown HCECs (siHCECs) were used. Confocal microscopy, transepithelial electrical resistance (TER), trypan blue exclusion assay and gentamicin invasion assay were done.

RESULTS

In primary and immortalized HCECs, IQGAP-1 co-localized with zonular occludin-1 (ZO-1) and actin. Enhanced actin and ZO-1 aggregation were seen in siHCECs. IQGAP-1 knockdown significantly increased TER of immortalized HCECs (P < .0001). Cell viability after PAK infection increased for siHCECs for up to 4 h after infection. PAK intracellular invasion was significantly lowered by 50% in siHCECs at 1 h post-infection.

CONCLUSION

IQGAP-1 knockdown increased the strength and integrity of tight junctions and may provide an early protective effect against P. aeruginosa invasion.

Resistance of the murine cornea to bacterial colonization during experimental dry eye

The healthy cornea is remarkably resistant to infection, quickly clearing deliberately inoculated bacteria such as Pseudomonas aeruginosa and Staphylococcus aureus. Contrasting with the adjacent conjunctiva and other body surfaces, it also lacks a resident viable bacterial microbiome. Corneal resistance to microbes depends on intrinsic defenses involving tear fluid and the corneal epithelium. Dry eye, an ocular surface disease associated with discomfort and inflammation, can alter tear fluid composition and volume, and impact epithelial integrity. We previously showed that experimentally-induced dry eye (EDE) in mice does not increase corneal susceptibility to P. aeruginosa infection. Here, we explored if EDE alters corneal resistance to bacterial colonization. EDE was established in mice using scopolamine injections and dehumidified air-flow, and verified by phenol-red thread testing after 5 and 10 days. As expected, EDE corneas showed increased fluorescein staining versus controls consistent with compromised epithelial barrier function. Confocal imaging using mT/mG knock-in mice with red-fluorescent membranes revealed no other obvious morphological differences between EDE corneas and controls for epithelium, stroma, and endothelium. EDE corneas were imaged ex vivo and compared to controls after alkyne-functionalized D-alanine labeling of metabolically-active colonizing bacteria, or by FISH using a universal 16S rRNA gene probe. Both methods revealed very few viable bacteria on EDE corneas after 5 or 10 days (median of 0, upper quartile of ≤ 1 bacteria per field of view for each group [9–12 eyes per group]) similar to control corneas. Furthermore, there was no obvious difference in abundance of conjunctival bacteria, which included previously reported filamentous forms. Thus, despite reduced tear flow and apparent compromise to corneal barrier function (fluorescein staining), EDE murine corneas continue to resist bacterial colonization and maintain the absence of a resident viable bacterial microbiome.

Unorthodox ophthalmic preparations on the Ghanaian market: a potential risk for ocular and enteric infections

PURPOSE

Microbial contamination of orthodox ophthalmic preparations poses a serious threat to the user by causing ocular infections. There is no such information about unorthodox ophthalmic preparations in a medical pluralistic system such as Ghana. The aim of this study was to assess unorthodox ophthalmic medications on the Ghanaian market for possible microbial contaminations.

METHODS

Unorthodox ophthalmic preparations were collected across different herbal and homeopathic outlets in Ghana. A total of 27 samples were collected from the ten (10) regions in Ghana. The samples were inoculated in different culture media (Plate count Agar, Blood Agar, MacConkey Agar, Saboraud Dextrose Agar). The microorganisms isolated were identified using standard microbiological procedures and antimicrobial susceptibility was done to determine whether they were resistant or susceptible strains.

RESULTS

All the samples were contaminated with bacteria and the majority were contaminated with fungus. A total of forty-eight bacteria spp. was isolated thus seven different types namely: Staphylococcus aureus, Bacilli spp., Serrati spp., Escherichia coli, Pseudomonas spp., Klebsiella spp. and Shigella spp. with Staphylococcus aureus being the predominant bacteria. For fungi, a total of eleven fungi species thus four different types namely: Cephalosporium spp., Penicillium spp., Cercosporium spp. and Clasdosporium spp. with the predominant fungi being Penicillium spp. Per the class of preparations, 15 contaminants were isolated from ten (10) anti-inflammatory preparations. The fungi were all susceptible to both Ketoconazole and Fluconazole but the bacteria were resistant to all the conventional antibiotics except Ciprofloxacin and Gentamycin.

CONCLUSION

Unorthodox ophthalmic preparations found on the Ghanaian market are contaminated with bacteria and fungi of clinical importance.

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.

Microbial safety implications of in-use topical diagnostic ophthalmic medications in eye clinics in Ghana

PURPOSE

To determine the microbial contaminants and its clinical importance in topical diagnostic ophthalmic medications (cycloplegics/mydriatics and miotics) in eye clinics in Ghana.

METHOD

A cross-section of eye clinics was sampled for the diagnostic agents (Atropine, Phenylephrine, Tropicamide and Cyclopentolate, Pilocarpine). Standard laboratory procedures and protocols were observed in culturing the samples on different Agars. Microscopy and various biochemical tests were performed to identify microbial species. Antimicrobial susceptibility testing was also performed to ascertain the clinical importance of the isolated microbes.

RESULTS

A total of 113 samples were obtained, from which 334 bacteria were isolated which included Bacilli spp. 91(27.25%), Coagulase Negative Staphylococci spp. 59(17.66%), Moraxella spp. 47(14.07%), Staphylococcus aureus 41(12.27%), Streptococcus spp. 21(6.29%), Klebsiella spp. 20(5.99%), Pseudomonas spp. 13(3.89%), Proteus spp. 12(3.59%), Escherichia coli. 12 (3.59%), Serratia spp. 10(2.99%), Shigella spp. 7(2.09%), Salmonella spp. 1(0.3%). There were 96 isolated fungal contaminants mainly Penicillium spp. 41(42.71%), Cephalosporium spp. 19(19.79%), Cladosporium spp. 15(15.63%), Aspergillus spp. 13(13.54%), Cercospora spp. 8(8.33%). The diagnostic agent with the most bacteria contamination was Phenylephrine 90 (26.95%) and the least being Pilocarpine 49 (14.67%). Also, the diagnostic agent with the most fungal contamination was Cyclopentolate 29 (30.2%) and the least was Tropicamide and Pilocarpine with 15 (15.63%) each. Gentamicin and Ciprofloxacin were the only antibiotics that showed 100% activity against all the bacterial isolates. Fungal contaminants were more susceptible to Ketoconazole as compared to Fluconazole.

CONCLUSION

Topical diagnostic ophthalmic preparations used in clinical settings in Ghana are contaminated with clinically important bacteria and fungi.

A novel murine model for contact lens wear reveals clandestine IL-1R dependent corneal parainflammation and susceptibility to microbial keratitis upon inoculation with Pseudomonas aeruginosa

PURPOSE

Contact lens wear carries a risk of complications, including corneal infection. Solving these complications has been hindered by limitations of existing animal models. Here, we report development of a new murine model of contact lens wear.

METHODS

C57BL/6 mice were fitted with custom-made silicone-hydrogel contact lenses with or without prior inoculation with Pseudomonas aeruginosa (PAO1-GFP). Contralateral eyes served as controls. Corneas were monitored for pathology, and examined ex vivo using high-magnification, time-lapse imaging. Fluorescent reporter mice allowed visualization of host cell membranes and immune cells. Lens-colonizing bacteria were detected by viable counts and FISH. Direct-colony PCR was used for bacterial identification.

RESULTS

Without deliberate inoculation, lens-wearing corneas remained free of visible pathology, and retained a clarity similar to non-lens wearing controls. CD11c-YFP reporter mice revealed altered numbers, and distribution, of CD11c-positive cells in lens-wearing corneas after 24 h. Worn lenses showed bacterial colonization, primarily by known conjunctival or skin commensals. Corneal epithelial cells showed vacuolization during lens wear, and after 5 days, cells with phagocyte morphology appeared in the stroma that actively migrated over resident keratocytes that showed altered morphology. Immunofluorescence confirmed stromal Ly6G-positive cells after 5 days of lens wear, but not in MyD88 or IL-1R gene-knockout mice. P. aeruginosa-contaminated lenses caused infectious pathology in most mice from 1 to 13 days.

CONCLUSIONS

This murine model of contact lens wear appears to faithfully mimic events occurring during human lens wear, and could be valuable for experiments, not possible in humans, that help solve the pathogenesis of lens-related complications.

Impact of topical corticosteroid pretreatment on susceptibility of the injured murine cornea to Pseudomonas aeruginosa colonization and infection

Research with animal models of Pseudomonas aeruginosa keratitis has shown that use of a topical corticosteroid alone against an established infection can significantly increase the number of colonizing bacteria or worsen clinical disease. Moreover, retrospective analysis has suggested that corticosteroid use in humans is associated with an increased risk of keratitis in eyes with pre-existing disease. Thus, while corticosteroids are often used to reduce ocular inflammation in the absence of infection, the risk of opportunistic infection remains a concern. However, the effect of corticosteroids on the intrinsic barrier function of uninfected corneas is unknown. Here, we tested if short-term topical corticosteroid treatment of an uninfected murine cornea would increase susceptibility to P. aeruginosa colonization or infection after epithelial injury. Topical prednisolone acetate (1%) was administered to one eye of C57BL/6 mice three times a day for 3 days; control eyes were treated with sterile PBS. Prior to inoculation with a cytotoxic P. aeruginosa corneal isolate strain 6206, corneas were subject to superficial-injury by tissue paper blotting, or scratch-injured followed by 12 h of healing. Previously we have shown that blotting renders mouse corneas susceptible to P. aeruginosa adhesion, but not infection, while 12 h healing reduces susceptibility to infection after scratching. Corneas were evaluated at 48 h for bacterial colonization and microbial keratitis (MK). To monitor impact on wound healing, corneal integrity was examined by fluorescein staining immediately after scarification and after 12 h healing. For both the tissue paper blotting and scratch-injury models, there was no significant difference in P. aeruginosa colonization at 48 h between corticosteroid-pretreated eyes and controls. With the blotting model, one case of MK was observed in a control (PBS-pretreated) cornea; none in corticosteroid-pretreated corneas. With the 12 h healing model, MK occurred in 6 of 17 corticosteroid-pretreated eyes versus 2 of 17 controls, a difference not statistically significant. Corticosteroid-pretreated eyes showed greater fluorescein staining 12 h after scarification injury, but this did not coincide with increased colonization or MK. Together, these data show that short-term topical corticosteroid therapy on an uninfected murine cornea does not necessarily enhance its susceptibility to P. aeruginosa colonization or infection after injury, even when it induces fluorescein staining.

Microbial contamination of multiple-use bottles of fluorescein ophthalmic solution

BACKGROUND

The contamination of ophthalmic solutions in ophthalmic practices remains an important cause of a myriad of secondary eye infections and a source of aggravation of ocular disorders such as corneal ulcers and keratitis. The aim of this study was to investigate the possible microbial contamination of fluorescein sodium dye solutions used in eye clinics in Ghana.

METHODS

Fluorescein sodium solutions were collected from various eye clinics in Ghana. Twenty-one samples of multiple-use fluorescein ophthalmic solutions were collected from various regions in Ghana. Eighteen unopened bottles yet to be used were also collected to serve as controls from the same facilities. The solutions were inoculated in different culture plates (blood agar, MacConkey agar, Sabouraud dextrose agar and plate count agar). The resulting microbial growth was identified using standard microbial identification techniques. Susceptibility tests were performed to ascertain the clinical importance of the organisms identified.

RESULTS

Positive cultures were recorded for all 21 multiple-use bottles (in-use) collected, but there were no positive cultures for the unopened bottles (yet to be used). Six different genera of bacteria were identified from fluorescein solutions, including resistant strains of Staphylococci spp., Bacillus spp., Klebsiella spp., Pseudomonas spp., Haemophilus spp. and Bordetella spp. Pseudomonas spp. were the most common bacterial contaminants. For fungi contaminations, Aspergillus spp., Penicillium spp. and Cladosporium spp. were isolated. The most common fungal contaminants were Aspergillus spp.

CONCLUSIONS

Multiple-use bottles of fluorescein solution used in eye clinics in Ghana were contaminated with clinically important strains of bacteria and fungi.

Opposing Effects of IL-1Ra and IL-36Ra on Innate Immune Response to Pseudomonas aeruginosa Infection in C57BL/6 Mouse Corneas

Pseudomonas aeruginosa keratitis is characterized by severe corneal ulceration and may lead to blindness if not treated properly in a timely manner. Although the roles of the IL-1 subfamily of cytokines are well established, as a newly discovered subfamily, IL-36 cytokine regulation, immunological relevance, and relation with IL-1 cytokines in host defense remain largely unknown. In this study, we showed that P. aeruginosa infection induces the expression of IL-36α and IL-36γ, as well as IL-1β and secreted IL-1Ra (sIL-1Ra), but not IL-36Ra. Downregulation of IL-1Ra increases, whereas downregulation of IL-36Ra decreases the severity of P. aeruginosa keratitis. IL-1R and IL-36Ra downregulation have opposing effects on the expression of IL-1β, sIL-1Ra, IL-36γ, S100A8, and CXCL10 and on the infiltration of innate immune cells. Administration of recombinant IL-1Ra improved, whereas IL-36Ra worsened the outcome of P. aeruginosa keratitis. Local application of IL-36γ stimulated the expression of innate defense molecules S100A9, mouse β-defensin 3, but suppressed IL-1β expression in B6 mouse corneas. IL-36γ diminished the severity of P. aeruginosa keratitis, and its protective effects were abolished in the presence of S100A9 neutralizing Ab and partially affected by CXCL10 and CXCR3 neutralizations. Thus, our data reveal that IL-1Ra and IL-36Ra have opposing effects on the outcome of P. aeruginosa keratitis and suggest that IL-36 agonists may be used as an alternative therapeutic to IL-1β-neutralizing reagents in controlling microbial keratitis and other mucosal infections.

IL-1R and MyD88 Contribute to the Absence of a Bacterial Microbiome on the Healthy Murine Cornea

Microbial communities are important for the health of mucosal tissues. Traditional culture and gene sequencing have demonstrated bacterial populations on the conjunctiva. However, it remains unclear if the cornea, a transparent tissue critical for vision, also hosts a microbiome. Corneas of wild-type, IL-1R (-/-) and MyD88 (-/-) C57BL/6 mice were imaged after labeling with alkyne-functionalized D-alanine (alkDala), a probe that only incorporates into the peptidoglycan of metabolically active bacteria. Fluorescence in situ hybridization (FISH) was also used to detect viable bacteria. AlkDala labeling was rarely observed on healthy corneas. In contrast, adjacent conjunctivae harbored filamentous alkDala-positive forms, that also labeled with DMN-Tre, a Corynebacterineae-specific probe. FISH confirmed the absence of viable bacteria on healthy corneas, which also cleared deliberately inoculated bacteria within 24 h. Differing from wild-type, both IL-1R (-/-) and MyD88 (-/-) corneas harbored numerous alkDala-labeled bacteria, a result abrogated by topical antibiotics. IL-1R (-/-) corneas were impermeable to fluorescein suggesting that bacterial colonization did not reflect decreased epithelial integrity. Thus, in contrast to the conjunctiva and other mucosal surfaces, healthy murine corneas host very few viable bacteria, and this constitutive state requires the IL-1R and MyD88. While this study cannot exclude the presence of fungi, viruses, or non-viable or dormant bacteria, the data suggest that healthy murine corneas do not host a resident viable bacterial community, or microbiome, the absence of which could have important implications for understanding the homeostasis of this tissue.

Keratin 6a reorganization for ubiquitin-proteasomal processing is a direct antimicrobial response

Chan et al. show that epithelial cells respond to bacterial components in the environment by releasing subunits of the keratin 6a (K6a) filament network to the cytosol for degradation by the ubiquitin–proteasome system. This generates antimicrobial peptides from K6a that are important for innate defense of the mucosal surface.

Skin and mucosal epithelia deploy antimicrobial peptides (AMPs) to eliminate harmful microbes. We reported that the intermediate filament keratin 6a (K6a) is constitutively processed into antimicrobial fragments in corneal epithelial cells. In this study, we show that K6a network remodeling is a host defense response that directly up-regulates production of keratin-derived AMPs (KAMPs) by the ubiquitin–proteasome system (UPS). Bacterial ligands trigger K6a phosphorylation at S19, S22, S37, and S60, leading to network disassembly. Mutagenic analysis of K6a confirmed that the site-specific phosphorylation augmented its solubility. K6a in the cytosol is ubiquitinated by cullin-RING E3 ligases for subsequent proteasomal processing. Without an appreciable increase in K6a gene expression and proteasome activity, a higher level of cytosolic K6a results in enhanced KAMP production. Although proteasome-mediated proteolysis is known to produce antigenic peptides in adaptive immunity, our findings demonstrate its new role in producing AMPs for innate immune defense. Manipulating K6a phosphorylation or UPS activity may provide opportunities to harness the innate immunity of epithelia against infection.

Contributions of MyD88-dependent receptors and CD11c-positive cells to corneal epithelial barrier function against Pseudomonas aeruginosa

Previously we reported that corneal epithelial barrier function against Pseudomonas aeruginosa was MyD88-dependent. Here, we explored contributions of MyD88-dependent receptors using vital mouse eyes and confocal imaging. Uninjured IL-1R (−/−) or TLR4 (−/−) corneas, but not TLR2 (−/−), TLR5 (−/−), TLR7 (−/−), or TLR9 (−/−), were more susceptible to P. aeruginosa adhesion than wild-type (3.8-fold, 3.6-fold respectively). Bacteria adherent to the corneas of IL-1R (−/−) or TLR5 (−/−) mice penetrated beyond the epithelial surface only if the cornea was superficially-injured. Bone marrow chimeras showed that bone marrow-derived cells contributed to IL-1R-dependent barrier function. In vivo, but not ex vivo, stromal CD11c+ cells responded to bacterial challenge even when corneas were uninjured. These cells extended processes toward the epithelial surface, and co-localized with adherent bacteria in superficially-injured corneas. While CD11c+ cell depletion reduced IL-6, IL-1β, CXCL1, CXCL2 and CXCL10 transcriptional responses to bacteria, and increased susceptibility to bacterial adhesion (>3-fold), the epithelium remained resistant to bacterial penetration. IL-1R (−/−) corneas also showed down-regulation of IL-6 and CXCL1 genes with and without bacterial challenge. These data show complex roles for TLR4, TLR5, IL-1R and CD11c+ cells in constitutive epithelial barrier function against P. aeruginosa, with details dependent upon in vivo conditions.

Disturbing the balance: effect of contact lens use on the ocular proteome and microbiome

Contact lens wear is a popular, convenient and effective method for vision correction. In recent years, contact lens practice has expanded to include new paradigms, including orthokeratology; however, their use is not entirely without risk, as the incidence of infection has consistently been reported to be higher in contact lens wearers. The explanations for this increased susceptibility have largely focused on physical damage, especially to the cornea, due to a combination of hypoxia, mechanical trauma, deposits and solution cytotoxicity, as well as poor compliance with care routines leading to introduction of pathogens into the ocular environment. However, in recent years, with the increasing availability and reduced cost of molecular techniques, the ocular environment has received greater attention with in-depth studies of proteins and other components. Numerous proteins were found to be present in the tears and their functions and interactions indicate that the tears are far more complex than formerly presumed. In addition, the concept of a sterile or limited microbial population on the ocular surface has been challenged by analysis of the microbiome. Ocular microbiome was not considered as one of the key sites for the Human Microbiome Project, as it was thought to be limited compared to other body sites. This was proven to be fallacious, as a wide variety of micro-organisms were identified in the analyses of human tears. Thus, the ocular environment is now recognised to be more complicated and interference with this ecological balance may lead to adverse effects. The use of contact lenses clearly changes the situation at the ocular surface, which may result in consequences which disturb the balance in the healthy eye.

Second harmonic generation imaging of corneal stroma after infection by Pseudomonas aeruginosa

Pseudomonas aeruginosa is a pathogenic gram-negative organism that has the ability to cause blinding corneal infections following trauma and during contact lens wear. In this study, we investigated the directional movement and orientation of an invasive corneal isolate of P. aeruginosa in the corneal stroma during infection of ex vivo and in vivo rabbit corneas using multiphoton fluorescence and second harmonic generation (SHG) imaging. Ex vivo, rabbit corneas were subject to three partial thickness wounds prior to inoculation. In vivo, New Zealand white rabbits were fit with P. aeruginosa laden contact lenses in the absence of a penetrating wound. At all time points tested, infiltration of the corneal stroma by P. aeruginosa revealed a high degree of alignment between the bacteria and collagen lamellae ex vivo (p < 0.001). In vivo, P. aeruginosa traveled throughout the stroma in discrete regions or bands. Within each region, the bacteria showed good alignment with collagen lamellae (P = 0.002). Interestingly, in both the in vitro and in vivo models, P. aeruginosa did not appear to cross the corneal limbus. Taken together, our findings suggest that P. aeruginosa exploits the precise spacing of collagen lamellae in the central cornea to facilitate spread throughout the stroma.

Corneal surface glycosylation is modulated by IL-1R and Pseudomonas aeruginosa challenge but is insufficient for inhibiting bacterial binding

Cell surface glycosylation is thought to be involved in barrier function against microbes at mucosal surfaces. Previously we showed that the epithelium of healthy mouse corneas becomes vulnerable to Pseudomonas aeruginosa adhesion if it lacks the innate defense protein MyD88 (myeloid differentiation primary response gene 88), or after superficial injury by blotting with tissue paper. Here we explored their effect on corneal surface glycosylation using a metabolic label, tetra-acetylated N-azidoacetylgalactosamine (Ac₄GalNAz). Ac₄GalNAz treatment labeled the surface of healthy mouse corneas, leaving most cells viable, and bacteria preferentially associated with GalNAz-labeled regions. Surprisingly, corneas from MyD88^-/- mice displayed similar GalNAz labeling to wild-type corneas, but labeling was reduced and patchy on IL-1 receptor (IL-1R)-knockout mouse corneas (P < 0.05, ANOVA). Tissue paper blotting removed GalNAz-labeled surface cells, causing DAPI labeling (permeabilization) of underlying cells. MS of material collected on the tissue paper blots revealed 67 GalNAz-labeled proteins, including intracellular proteins. These data show that the normal distribution of surface glycosylation requires IL-1R, but not MyD88, and is not sufficient to prevent bacterial binding. They also suggest increased P. aeruginosa adhesion to MyD88^-/- and blotted corneas is not due to reduction in total surface glycosylation, and for tissue paper blotting is likely due to cell permeabilization.-Jolly, A. L., Agarwal, P., Metruccio, M. M. E., Spiciarich, D. R., Evans, D. J., Bertozzi, C. R., Fleiszig, S. M. J. Corneal surface glycosylation is modulated by IL-1R and Pseudomonas aeruginosa challenge but is insufficient for inhibiting bacterial binding.

Ex vivo rabbit and human corneas as models for bacterial and fungal keratitis

PURPOSE

In the study of microbial keratitis, in vivo animal models often require a large number of animals, and in vitro monolayer cell culture does not maintain the three-dimensional structure of the tissues or cell-to-cell communication of in vivo models. Here, we propose reproducible ex vivo models of single- and dual-infection keratitis as an alternative to in vivo and in vitro models.

METHODS

Excised rabbit and human corneoscleral rims maintained in organ culture were infected using 10⁸ cells of Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans or Fusarium solani. The infection was introduced by wounding with a scalpel and exposing corneas to the microbial suspension or by intrastromal injection. Post-inoculation, corneas were maintained for 24 and 48 h at 37 °C. After incubation, corneas were either homogenised to determine colony-forming units (CFU)/cornea or processed for histological examination using routine staining methods. Single- and mixed-species infections were compared.

RESULTS

We observed a significant increase in CFU after 48 h compared to 24 h with S. aureus and P. aeruginosa. However, no such increase was observed in corneas infected with C. albicans or F. solani. The injection method yielded an approximately two- to 100-fold increase (p < 0.05) in the majority of organisms from infected corneas. Histology of the scalpel-wounded and injection models indicated extensive infiltration of P. aeruginosa throughout the entire cornea, with less infiltration observed for S. aureus, C. albicans and F. solani. The models also supported dual infections.

CONCLUSIONS

Both scalpel wounding and injection methods are suitable for inducing infection of ex vivo rabbit and human cornea models. These simple and reproducible models will be useful as an alternative to in vitro and in vivo models for investigating the detection and treatment of microbial keratitis, particularly when this might be due to two infective organisms.

Human Tear Fluid Reduces Culturability of Contact Lens-Associated Pseudomonas aeruginosa Biofilms but Induces Expression of the Virulence-Associated Type III Secretion System

PURPOSE

The type III secretion system (T3SS) is a significant virulence determinant for Pseudomonas aeruginosa. Using a rodent model, we found that contact lens (CL)-related corneal infections were associated with lens surface biofilms. Here, we studied the impact of human tear fluid on CL-associated biofilm growth and T3SS expression.

METHODS

P. aeruginosa biofilms were formed on contact lenses for up to 7 days with or without human tear fluid, then exposed to tear fluid for 5 or 24 h. Biofilms were imaged using confocal microscopy. Bacterial culturability was quantified by viable counts, and T3SS gene expression measured by RT-qPCR. Controls included trypticase soy broth, PBS and planktonic bacteria.

RESULTS

With or without tear fluid, biofilms grew to ∼10⁸ CFU viable bacteria by 24 h. Exposing biofilms to tear fluid after they had formed without it on lenses reduced bacterial culturability ∼180-fold (P<.001). CL growth increased T3SS gene expression versus planktonic bacteria [5.46 ± 0.24-fold for T3SS transcriptional activitor exsA (P=.02), and 3.76 ± 0.36-fold for T3SS effector toxin exoS (P=.01)]. Tear fluid further enhanced exsA and exoS expression in CL-grown biofilms, but not planktonic bacteria, by 2.09 ± 0.38-fold (P=.04) and 1.89 ± 0.26-fold (P<.001), respectively.

CONCLUSIONS

Considering the pivitol role of the T3SS in P. aeruginosa infections, its induction in CL-grown P. aeruginosa biofilms by tear fluid might contribute to the pathogenesis of CL-related P. aeruginosa keratitis.

Pseudomonas aeruginosa Outer Membrane Vesicles Triggered by Human Mucosal Fluid and Lysozyme Can Prime Host Tissue Surfaces for Bacterial Adhesion

Pseudomonas aeruginosa is a leading cause of human morbidity and mortality that often targets epithelial surfaces. Host immunocompromise, or the presence of indwelling medical devices, including contact lenses, can predispose to infection. While medical devices are known to accumulate bacterial biofilms, it is not well understood why resistant epithelial surfaces become susceptible to P. aeruginosa. Many bacteria, including P. aeruginosa, release outer membrane vesicles (OMVs) in response to stress that can fuse with host cells to alter their function. Here, we tested the hypothesis that mucosal fluid can trigger OMV release to compromise an epithelial barrier. This was tested using tear fluid and corneal epithelial cells in vitro and in vivo. After 1 h both human tear fluid, and the tear component lysozyme, greatly enhanced OMV release from P. aeruginosa strain PAO1 compared to phosphate buffered saline (PBS) controls (∼100-fold). Transmission electron microscopy (TEM) and SDS-PAGE showed tear fluid and lysozyme-induced OMVs were similar in size and protein composition, but differed from biofilm-harvested OMVs, the latter smaller with fewer proteins. Lysozyme-induced OMVs were cytotoxic to human corneal epithelial cells in vitro and murine corneal epithelium in vivo. OMV exposure in vivo enhanced Ly6G/C expression at the corneal surface, suggesting myeloid cell recruitment, and primed the cornea for bacterial adhesion (∼4-fold, P < 0.01). Sonication disrupted OMVs retained cytotoxic activity, but did not promote adhesion, suggesting the latter required OMV-mediated events beyond cell killing. These data suggest that mucosal fluid induced P. aeruginosa OMVs could contribute to loss of epithelial barrier function during medical device-related infections.

Contact lens associated microbial keratitis: practical considerations for the optometrist

Microbial keratitis (MK) is a corneal condition that encompasses several different pathogens and etiologies. While contact lens associated MK is most often associated with bacterial infections, other pathogens (fungi, Acanthamoeba species, etc) may be responsible. This review summarizes the risk factors, microbiology, diagnostic characteristics, and treatment options for all forms of contact lens-related MK.

A novel in vivo corneal trans-epithelial electrical resistance measurement device

PURPOSE

To develop a device that is capable of easily measuring corneal transepithelial electrical resistance (TER) and changes in the corneal barrier function.

METHODS

We had previously developed an in vivo method for measuring corneal TER using intraocular electrode. This method can be used to precisely measure the decline of the corneal barrier function after instillation of benzalkonium chloride (BAC). In order to lessen the invasiveness of that procedure, we further refined the method for measuring the corneal TER by developing electrodes that could be placed on the cornea and in the conjunctival sac instead of inserting them into the anterior chamber. TER was then calculated by subtracting the electrical resistance, which lacked the corneal epithelial input, from the whole electrical resistance that was measured between the electrodes. Slit lamp examination and scanning electron microscopy (SEM) were used to determine safety of the new device. Corneal TER changes after exposure to 0.02% BAC were determined using the new device as well as SEM and transmission electron microscopy (TEM).

RESULTS

Slit lamp examination before and after exposure of rabbits' corneas to the sensor confirmed safety of the device. SEM examination revealed no difference of the corneal epithelium which exposed to the new device with normal corneas. SEM and TEM pictures revealed damaged microvilli and tight junctions after instillation of 0.02% BAC. TER change after treatment with 0.02%BAC was similar to those determined by the established anterior chamber method.

CONCLUSION

We succeeded to develop a less invasive device for corneal TER measurement in vivo in animals. This new device may be applicable in the future for clinical use in humans.

Corneal Biofilms: From Planktonic to Microcolony Formation in an Experimental Keratitis Infection with Pseudomonas Aeruginosa

PURPOSE

Microbial biofilms commonly comprise part of the infectious scenario, complicating the therapeutic approach. The purpose of this study was to determine in a mouse model of corneal infection if mature biofilms formed and to visualize the stages of biofilm formation.

METHODS

A bacterial keratitis model was established using Pseudomonas aeruginosa ATCC 9027 (1 × 10(8) CFU/ml) to infect the cornea of C57BL/6 black mouse. Eyes were examined post-infection (PI) on days 1, 2, 3, 5, and 7, and imaged by slit lamp microscopy, and light, confocal, and electron microscopy to identify the stages of biofilm formation and the time of appearance.

RESULTS

On PI day 1, Gram staining showed rod-shaped bacteria adherent on the corneal surface. On PI days 2 and 3, bacteria were seen within webs of extracellular polymeric substance (EPS) and glycocalyx secretion, imaged by confocal microscopy. Scanning electron microscopy demonstrated microcolonies of active infectious cells bound with thick fibrous material. Transmission electron microscopy substantiated the formation of classical biofilm architecture with P. aeruginosa densely packed within the extracellular polymeric substances on PI days 5 and 7.

CONCLUSION

Direct visual evidence showed that biofilms routinely developed on the biotic surface of the mouse cornea. The mouse model can be used to develop new approaches to deal therapeutically with biofilms in corneal infections.

The importance of the Pseudomonas aeruginosa type III secretion system in epithelium traversal depends upon conditions of host susceptibility

Pseudomonas aeruginosa is invasive or cytotoxic to host cells, depending on the type III secretion system (T3SS) effectors encoded. While the T3SS is known to be involved in disease in vivo, how it participates remains to be clarified. Here, mouse models of superficial epithelial injury (tissue paper blotting with EGTA treatment) and immunocompromise (MyD88 deficiency) were used to study the contribution of the T3SS transcriptional activator ExsA to epithelial traversal. Corneas of excised eyeballs were inoculated with green fluorescent protein (GFP)-expressing PAO1 or isogenic exsA mutants for 6 h ex vivo before bacterial traversal and epithelial thickness were quantified by using imaging. In the blotting-EGTA model, exsA mutants were defective in capacity for traversal. Accordingly, an ∼16-fold variability in exsA expression among PAO1 isolates from three sources correlated with epithelial loss. In contrast, MyD88-/- epithelia remained susceptible to P. aeruginosa traversal despite exsA mutation. Epithelial lysates from MyD88-/- mice had reduced antimicrobial activity compared to those from wild-type mice with and without prior antigen challenge, particularly 30- to 100-kDa fractions, for which mass spectrometry revealed multiple differences, including (i) lower baseline levels of histones, tubulin, and lumican and (ii) reduced glutathione S-transferase, annexin, and dermatopontin, after antigen challenge. Thus, the importance of ExsA in epithelial traversal by invasive P. aeruginosa depends on the compromise enabling susceptibility, suggesting that strategies for preventing infection will need to extend beyond targeting the T3SS. The data also highlight the importance of mimicking conditions allowing susceptibility in animal models and the need to monitor variability among bacterial isolates from different sources, even for the same strain.

Matrix Metalloproteinase-13 as a Target for Suppressing Corneal Ulceration Caused by Pseudomonas aeruginosa Infection

PURPOSE

Pseudomonas aeruginosa keratitis is characterized by severe corneal ulceration. This study investigated whether matrix metalloproteinase-13 (MMP13) is involved in P. aeruginosa-induced corneal ulceration and whether it therefore can be targeted for preventing P. aeruginosa keratitis.

METHODS

MMP13 expression in P. aeruginosa-infected C57BL/6 mouse corneas was assessed by quantitative polymerase chain reaction and immunohistochemistry analyses. An MMP13-inhibitor (MMP13i) was either injected subconjunctivally prior to or coapplied topically with gatifloxacin 16 hours after infection. Disease severity was assessed by corneal imaging, clinical scoring, bacterial burden, neutrophil infiltration, and CXCL2 expression. Corneal damage and infiltration were also determined by immunohistochemistry analysis and whole-mount confocal microscopy.

RESULTS

P. aeruginosa infection induced an increased expression of MMP13 in mouse corneas from 6 to 24 hours after infection in a Toll-liked receptor 5-dependent manner. Subconjunctival injection of MMP13i prior to P. aeruginosa inoculation significantly decreased keratitis severity, as evidenced by preserved epithelium integrity and intact basement membrane, leading to reduced bacterial dissemination to the stroma. Furthermore, topical coapplication of MMP13i with gatifloxacin greatly improved disease outcomes, including accelerated opacity dissolution; decreased inflammation, cellular infiltration, and collagen disorganization; and basement membrane preservation.

CONCLUSIONS

Elevated MMP13 activity may contribute to P. aeruginosa keratitis through basement membrane degradation, and its inhibition could potentially be used as an adjunctive therapy to treat microbial keratitis and other mucosal infections.

Histopathological Studies on Rabbits Infected by Bacteria Causing Infectious Keratitis in Human through Eye Inoculation

AIM

This study aimed to investigate the pathogenic effect of bacteria causing infectious keratitis among patients through experimental study conducted on rabbits' eyes with the aid of histopathology as eye infection is a common disease in developing countries that may complicate to loss of vision.

METHODOLOGY

100 swab samples were collected from human infected eyes, at Qassim region during 2012, for the isolation of Pseudomonas aeruginosa and Staphylococcus aureus. The isolated pathogenic bacteria were tested to various antibiotics using some selected antibiotics discs through agar-well diffusion method. Then, experimental study conducted on 27 rabbits. The rabbits were divided randomly into three equal groups, each containing 9 rabbits. Rabbits of group (1) served as control group (Negative Control) and their eyes were inoculated with the buffer only. Rabbits of group (2) were inoculated through eyes with the isolated Pseudomonas aeruginosa. Rabbits of group (3) were inoculated through eyes with the isolated Staphylococcus aureus.

RESULTS

Out of 100 collected swab samples from human infected eyes, Pseudomonas aeruginosa and Staphylococcus aureus were isolated with a total percentage of 25.21% and 15.65%; respectively and used in this study. Both bacterial isolates were sensitive to Gentamicin and Cefuroxime. Clinically, experimentally infected rabbits by Pseudomonas aeruginosa, revealed varying degree corneal abrasions, corneal abscess and dense corneal opacity. Histopathologically, at 3(rd) day post-infection (PI), the cornea revealed polymorpho-nuclear cells infiltration with loss of the outer epithelial lining. At 7(th) day PI, neutrophils were seen in the stroma. At 15(th) day PI, proliferation of fibroblasts and new vascularisation were seen in the stroma. Clinically, rabbits experimentally infected with Staphylococcus aureus, revealed corneal ulcers and focal abscesses. Histopathologically, at 3(rd) and 7(th) day PI, the cornea revealed edema and infiltration of leukocytes. At 15(th) day PI, hyperplasia of corneal epithelium and proliferation of keratocytes were evident. The liver and kidneys of experimented rabbits revealed no remarkable histopathological alterations along the period of experiment.

CONCLUSION

Pseudomonas aeruginosa and Staphylococcus aureus are common eye infection in human, both induced severe lesions in the eyes of rabbits that could interfere with vision, therefore, strict measures to control these infections in human is recommended.

Pseudomonas aeruginosa infectious keratitis in a high oxygen transmissible rigid contact lens rabbit model

PURPOSE

To establish a rabbit model of infectious Pseudomonas aeruginosa keratitis using ultrahigh oxygen transmissible rigid lenses and characterize the frequency and severity of infection when compared to a non-oxygen transmissible lens material.

METHODS

Rabbits were fit with rigid lenses composed of ultrahigh and non-oxygen transmissible materials. Prior to wear, lenses were inoculated with an invasive corneal isolate of P. aeruginosa stably conjugated to green fluorescent protein (GFP). Corneas were examined before and after lens wear using a modified Heidelberg Rostock Tomograph in vivo confocal microscope. Viable bacteria adherent to unworn and worn lenses were assessed by standard plate counts. The presence of P. aeruginosa-GFP and myeloperoxidase-labeled neutrophils in infected corneal tissue was evaluated using laser scanning confocal microscopy.

RESULTS

The frequency and severity of infectious keratitis was significantly greater with inoculated ultrahigh oxygen transmissible lenses. Infection severity was associated with increasing neutrophil infiltration and in severe cases, corneal melting. In vivo confocal microscopic analysis of control corneas following lens wear confirmed that hypoxic lens wear was associated with mechanical surface damage, whereas no ocular surface damage was evident in the high-oxygen lens group.

CONCLUSIONS

These data indicate that in the absence of adequate tear clearance, the presence of P. aeruginosa trapped under the lens overrides the protective effects of oxygen on surface epithelial cells. These findings also suggest that alternative pathophysiological mechanisms exist whereby changes under the lens in the absence of frank hypoxic damage result in P. aeruginosa infection in the otherwise healthy corneal epithelium.

En-face optical coherence tomography as a novel tool for exploring the ocular surface: a pilot comparative study to conventional B-scans and in vivo confocal microscopy

PURPOSE

To explore the potential of spectral-domain optical coherence tomography (SD-OCT) using the en-face technology for the imaging of ocular surface diseases and to correlate the findings with in vivo confocal microscopy (IVCM) images.

PATIENTS AND METHODS

113 eyes of 75 subjects with various ocular surface diseases were investigated with the RTVue(®) anterior-segment en face OCT. En face OCT images were compared to B-scan OCT and IVCM images.

RESULTS

Patients with corneal dystrophies, corneal deposits, keratitis, pterygium, conjunctivochalasis, or ocular surface squamous neoplasia and patients who underwent lamellar corneal surgeries were included. En-face OCT images showed ocular surface tissue changes that were not discernible using conventional B-scan OCT. Nevertheless, there was a good correlation with IVCM analysis. Compared with IVCM, the major advantages of en-face OCT included easy operation and rapid image acquisition, with minimal operator experience required. In addition, the non-contact method avoided patient discomfort and external pressure on the globe, which was especially useful in patients with corneal dystrophies, ulcers, or corneal abscesses. Although the resolution of en-face OCT was lower than that of IVCM, it allowed useful overall visualization of corneal lesions due to the larger areas analyzed.

CONCLUSION

En-face SD-OCT is a novel, valuable tool to assess a wide variety of ocular surface diseases. It can provide additional information and new insight into different ocular surface conditions with no corneal contact.

Mechanisms of phagocytosis and host clearance of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic bacterial pathogen responsible for a high incidence of acute and chronic pulmonary infection. These infections are particularly prevalent in patients with chronic obstructive pulmonary disease and cystic fibrosis: much of the morbidity and pathophysiology associated with these diseases is due to a hypersusceptibility to bacterial infection. Innate immunity, primarily through inflammatory cytokine production, cellular recruitment, and phagocytic clearance by neutrophils and macrophages, is the key to endogenous control of P. aeruginosa infection. In this review, we highlight recent advances toward understanding the innate immune response to P. aeruginosa, with a focus on the role of phagocytes in control of P. aeruginosa infection. Specifically, we summarize the cellular and molecular mechanisms of phagocytic recognition and uptake of P. aeruginosa, and how current animal models of P. aeruginosa infection reflect clinical observations in the context of phagocytic clearance of the bacteria. Several notable phenotypic changes to the bacteria are consistently observed during chronic pulmonary infections, including changes to mucoidy and flagellar motility, that likely enable or reflect their ability to persist. These traits are likewise examined in the context of how the bacteria avoid phagocytic clearance, inflammation, and sterilizing immunity.

Antimicrobial compounds in tears

The tear film coats the cornea and conjunctiva and serves several important functions. It provides lubrication, prevents drying of the ocular surface epithelia, helps provide a smooth surface for refracting light, supplies oxygen and is an important component of the innate defense system of the eye providing protection against a range of potential pathogens. This review describes both classic antimicrobial compounds found in tears such as lysozyme and some more recently identified such as members of the cationic antimicrobial peptide family and surfactant protein-D as well as potential new candidate molecules that may contribute to antimicrobial protection. As is readily evident from the literature review herein, tears, like all mucosal fluids, contain a plethora of molecules with known antimicrobial effects. That all of these are active in vivo is debatable as many are present in low concentrations, may be influenced by other tear components such as the ionic environment, and antimicrobial action may be only one of several activities ascribed to the molecule. However, there are many studies showing synergistic/additive interactions between several of the tear antimicrobials and it is highly likely that cooperativity between molecules is the primary way tears are able to afford significant antimicrobial protection to the ocular surface in vivo. In addition to effects on pathogen growth and survival some tear components prevent epithelial cell invasion and promote the epithelial expression of innate defense molecules. Given the protective role of tears a number of scenarios can be envisaged that may affect the amount and/or activity of tear antimicrobials and hence compromise tear immunity. Two such situations, dry eye disease and contact lens wear, are discussed here.

Interferon regulatory factor-1 in flagellin-induced reprogramming: potential protective role of CXCL10 in cornea innate defense against Pseudomonas aeruginosa infection

PURPOSE

We previously showed that pre-exposure of the cornea to Toll-like receptor (TLR)5 ligand flagellin induces strong protective innate defense against microbial pathogens and hypothesized that flagellin modulates gene expression at the transcriptional levels. Thus, we sought to determine the role of one transcription factor, interferon regulatory factor (IRF1), and its target gene CXCL10 therein.

METHODS

Superarray was used to identify transcription factors differentially expressed in Pseudomonas aeruginosa-challenged human corneal epithelial cells (CECs) with or without flagellin pretreatment. The expression of CXCL10, IRF1, LI-8(CXCL2), and IFNγ was determined by PCR, immunohistochemistry, Western/dot blotting, and/or ELISA. IRF1 knockout mice, CXCL10 and IFNγ neutralization, and NK cell depletion were used to define in vivo regulation and function of CXCL10. The severity of P. aeruginosa was assessed using clinical scoring, slit-lamp microscopy, bacterial counting, polymorphonuclear leukocytes (PMN) infiltration, and macrophage inflammatory protein 2/Chemokine (C-X-C motif) ligand 2 (MIP-2/CXCL2) expression.

RESULTS

Flagellin pretreatment drastically affected P. aeruginosa-induced IRF1 expression in human CECs. However, flagellin pretreatment augmented the P. aeruginosa-induced expression of Irf1 and its target gene Cxcl10 in B6 mouse corneas. Irf1 deficiency reduced infection-triggered CXCL10 expression, increased keratitis severity, and attenuated flagellin-elicited protection compared to values in wild-type (WT) controls. CXCL10 neutralization in the cornea of WT mice displayed pathogenesis similar to that of IRF1⁻/⁻ mice. IFNγ receptor neutralization and NK cell depletion prevented flagellin-augmented IRF1 and CXCL10 expression and increased the susceptibility to P. aeruginosa infection in mouse corneas.

CONCLUSIONS

IRF1 plays a role in the corneal innate immune response by regulating CXCL10 expression. IFNγ-producing NK cells augment the epithelial expression of IRF1 and CXCL10 and thus contribute to the innate defense of the cornea against P. aeruginosa infection.

Rho GTPases and regulation of cell migration and polarization in human corneal epithelial cells

Purpose

Epithelial cell migration is required for regeneration of tissues and can be defective in a number of ocular surface diseases. This study aimed to determine the expression pattern of Rho family small G-proteins in human corneal epithelial cells to test their requirement in directional cell migration.

Methods

Rho family small G-protein expression was assessed by reverse transcription-polymerase chain reaction. Dominant-inhibitory constructs encoding Rho proteins or Rho protein targeting small interfering RNA were transfected into human corneal epithelial large T antigen cells, and wound closure rate were evaluated by scratch wounding assay, and a complementary non-traumatic cell migration assay. Immunofluorescence staining was performed to study cell polarization and to assess Cdc42 downstream effector.

Results

Cdc42, Chp, Rac1, RhoA, TC10 and TCL were expressed in human corneal epithelial cells. Among them, Cdc42 and TCL were found to significantly affect cell migration in monolayer scratch assays. These results were confirmed through the use of validated siRNAs directed to Cdc42 and TCL. Scramble siRNA transfected cells had high percentage of polarized cells than Cdc42 or TCL siRNA transfected cells at the wound edge. We showed that the Cdc42-specific effector p21-activated kinase 4 localized predominantly to cell-cell junctions in cell monolayers, but failed to translocate to the leading edge in Cdc42 siRNA transfected cells after monolayer wounding.

Conclusion

Rho proteins expressed in cultured human corneal epithelial cells, and Cdc42, TCL facilitate two-dimensional cell migration in-vitro. Although silencing of Cdc42 and TCL did not noticeably affect the appearance of cell adhesions at the leading edge, the slower migration of these cells indicates both GTP-binding proteins play important roles in promoting cell movement of human corneal epithelial cells.

IL-17 plays a central role in initiating experimental Candida albicans infection in mouse corneas

The pathogenesis of fungal infection in the cornea remains largely unclear. To understand how the immune system influences the progression of fungal infection in corneas, we inoculated immunocompetent BALB/c mice, neutrophil- or CD4⁺ T-cell-depleted BALB/c mice, and nude mice with Candida albicans. We found that only immunocompetent BALB/c mice developed typical Candida keratitis (CaK), while the other mouse strains lacked obvious clinical manifestations. Furthermore, CaK development was blocked in immunocompetent mice treated with anti-IL-17A or anti-IL-23p19 to neutralize IL-17 activity. However, no significant effects were observed when Treg cells, γδ T cells, or IFN-γ were immunodepleted. Upon infection, the corneas of BALB/c mice were infiltrated with IL-17-producing leukocytes, including neutrophils and, to a lesser degree, CD4⁺ T cells. In contrast, leukocyte recruitment to corneas was significantly diminished in nude mice. Indeed, nude mice produced much less chemokines (e.g. CXCL1, CXCL2, CXCL10, CXCL12, CCL2, and IL-6) in response to inoculation. Remarkably, addition of CXCL2 during inoculation restored CaK induction in nude mice. In contrast to its therapeutic effect on CaK, neutralization of IL-17 exacerbated Candida-induced dermatitis in skin. We conclude that IL-17, mainly produced by neutrophils and CD4⁺ T cells in the corneas, is essential in the pathogenesis of CaK.

β-Catenin promotes host resistance against Pseudomonas aeruginosa keratitis

OBJECTIVE

To explore the role of β-catenin in Pseudomonas aeruginosa (PA) keratitis.

METHODS

Western-blot and immunostaining assay were used to determine the β-catenin protein expression in C57BL/6 (B6) corneas and in in vitro cultured murine cells including macrophage-like RAW264.7 cells, bone marrow-derived neutrophils and A6(1) corneal epithelial cells. B6 mice were subconjunctivally injected with lentivirus expressing active mutant of β-catenin (β-cat-lentivirus) vs appropriate control (Ctl-lentivirus), and then infected with PA. Pro-inflammatory cytokine levels were examined using real-time PCR and ELISA, and bacterial burden was assessed using plate count assays both in vivo and in vitro.

RESULTS

β-Catenin protein expression was decreased in B6 corneas, murine macrophage-like RAW264.7 cells, mouse bone marrow-derived neutrophils and mouse A6(1) corneal epithelial cells after PA infection. Over-expression of β-catenin in B6 corneas significantly reduced the severity of corneal disease after PA infection, by decreasing pro-inflammatory cytokine expression and bacterial burden. In vitro data further demonstrated that over-expression of β-catenin suppressed pro-inflammatory cytokine production but enhanced bacterial clearance in macrophages and neutrophils.

CONCLUSIONS

β-Catenin reduces the severity of PA keratitis by decreasing corneal inflammation and bacterial burden.