Staphylococcus aureus-induced corneal inflammation is dependent on Toll-like receptor 2 and myeloid differentiation factor 88

Toll-like receptors (TLRs) expressed by the corneal epithelium represent a first line of host defense to microbial keratitis. The current study examined the role of TLR2, TLR4, and TLR9 and the common adaptor molecule myeloid differentiation factor 88 (MyD88) in a Staphylococcus aureus model of corneal inflammation. The corneal epithelia of C57BL/6, TLR2(-/-), TLR4(-/-), TLR9(-/-), and MyD88(-/-) mice were abraded using a trephine and epithelial brush and were exposed to heat- or UV-inactivated S. aureus clinical strain 8325-4 and other clinical isolates. Corneal thickness and haze were measured by in vivo confocal microscopy, neutrophil recruitment to the corneal stroma was quantified by immunohistochemistry, and cytokine production was measured by enzyme-linked immunosorbent assay. The exposure of corneal epithelium to S. aureus induced neutrophil recruitment to the corneal stroma and increased corneal thickness and haze in control C57BL/6 mice but not in TLR2(-/-) or MyD88(-/-) mice. The responses of TLR4(-/-) and TLR9(-/-) mice were similar to those of C57BL/6 mice. S. aureus-induced cytokine production by corneal epithelial cells and neutrophils was also significantly reduced in TLR2(-/-) mice compared with that in C57BL/6 mice. These findings indicate that S. aureus-induced corneal inflammation is mediated by TLR2 and MyD88 in resident epithelial cells and infiltrating neutrophils.

Salicylic acid reduces the production of several potential virulence factors of Pseudomonas aeruginosa associated with microbial keratitis

PURPOSE

Pseudomonas aeruginosa is a common cause of contact-lens-related microbial keratitis. This bacterium is becoming increasingly resistant to antibiotics, and even if the infection can be treated with antibiotics, damage to the cornea resulting from the combined effect of bacteria and host factors can lead to loss of vision. The purpose of this study was to test the effect of salicylic acid on the production of potential virulence factors during the growth of P. aeruginosa.

METHODS

Bacterial cells were grown in a subinhibitory concentration of salicylic acid, and supernatants were collected and analyzed for presence of proteases by using zymography and hydrolysis of chromogenic substrates. The supernatants were also analyzed for the amount of acetylated homoserine lactones by using bacterial reporter strains. Pseudomonas cells from salicylic acid cultures were analyzed for their twitching and swimming motility as well as their ability to invade or cause the death of corneal epithelial cells.

RESULTS

Growth in a subinhibitory concentration of salicylic acid resulted in a significant reduction in the number of bacterial cells and a reduction in the rate of the number of bacteria increasing during logarithmic growth, but the time to reach the stationary phase of growth was unchanged. These changes in growth pattern affected the amount of acylated homoserine lactones produced by P. aeruginosa 6294. Also affected by growth in salicylic acid was the ability of strain 6294 to show twitching or swimming motility. Salicylic acid also reduced the invasion of strain 6294 into corneal epithelial cells and the epithelial cell death caused by strain 6206. Furthermore, production of proteases by P. aeruginosa was significantly reduced by growth in salicylic acid.

CONCLUSIONS

The results of this study clearly demonstrate that salicylic acid has a significant impact on several potential virulence factors of P. aeruginosa that may be involved in the production of microbial keratitis. These effects were probably mediated by reduction in the cell density and concomitant reduction in the quorum-sensing signaling molecules, the acylated homoserine lactones, produced by P. aeruginosa.

Prolonged hypoxia induces lipid raft formation and increases Pseudomonas internalization in vivo after contact lens wear and lid closure

PURPOSE

To investigate the effects of hypoxia on lipid raft formation and Pseudomonas aeruginosa internalization by the corneal epithelium with and without the physical effects of contact lens wear.

METHODS

One eye of each rabbit was randomly fitted with a low-Dk rigid gas-permeable contact lens (LDCTL) or closed with sutures, with the other as a control. After 1 day or 3 days, the rabbits were killed and bacterial invasion was assessed by gentamicin survival assay. Lipid rafts were identified by staining with FITC-conjugated beta subunit of cholera toxin. Corneal epithelial Bcl-2 expression was detected by Western blotting; surface epithelial cell size and thickness (epithelium and stroma) were measured by confocal microscopy.

RESULTS

One-day hypoxia induced no significant changes in P. aeruginosa internalization, Bcl-2 expression, or lipid raft formation except in one of four eyelid-closed eyes. After 3 days, P. aeruginosa internalization was increased significantly (P < 0.05) in LDCTL-wearing eyes and not significantly (P = 0.10) increased in eyelid-closed eyes. Both 3-day test conditions also induced lipid raft-forming cells that bound P. aeruginosa, albeit in different regions of the cornea (peripherally in LDCTL-wearing eyes and centrally in closed eyes); did not alter epithelial thickness or surface cell size; and appeared to decrease epithelial Bcl-2 expression.

CONCLUSIONS

This is the first direct comparison in vivo between two different methods inducing hypoxia on the corneal surface. Association of P. aeruginosa internalization with lipid raft formation in both conditions suggests a critical link among prolonged hypoxia, lipid raft formation, and susceptibility to P. aeruginosa infection. However, different distribution patterns of lipid raft-forming cells suggest physical effects of contact lens wear may direct localization of lipid raft-associated P. aeruginosa internalization on the corneal surface.

Effects of Moraxella (Branhamella) ovis culture filtrates on bovine erythrocytes, peripheral mononuclear cells, and corneal epithelial cells

Infectious bovine keratoconjunctivitis (IBK) is a highly contagious ocular disease that affects cattle of all ages and that occurs worldwide. Piliated hemolytic Moraxella bovis is recognized as the etiologic agent of IBK. According to data from the Nebraska Veterinary Diagnostic Laboratory System, however, Moraxella (Branhamella) ovis has been isolated with increasing frequency from cattle affected with IBK. The objective of this study was, therefore, to examine M. ovis field isolates for the presence of the putative virulence factors of M. bovis. Culture filtrates from selected M. ovis field isolates demonstrated hemolytic activity on bovine erythrocytes and cytotoxic activity on bovine peripheral blood mononuclear cells and corneal epithelial cells. The hemolytic activity of the culture filtrates was attenuated after heat treatment. Polyclonal antibodies raised against the M. bovis hemolysin-cytotoxin also recognized a protein of approximately 98 kDa in a Western blot assay. These data indicate that the M. ovis field isolates examined produce one or more heat-labile exotoxins and may suggest that M. ovis plays a role in the pathogenesis of IBK.

Interaction of Pseudomonas aeruginosa with human tear fluid components

PURPOSE

Reflex human tears bind Pseudomonas aeruginosa bacteria and prevent them from invading corneal epithelial cells. In this study, we assessed the effect of eye closure and the role of sialoglycoprotein (SG) in tears on bacterial binding and invasion.

METHODS

Human tears (reflex and closed-eye) were collected using a microcapillary tube. Reflex tears were separated into 13 fractions by high-performance liquid chromatography while high-molecular-weight components from closed-eye tears were separated into an SG/mucin fraction and a nonmucin fraction. Bacterial binding was quantified by viable counts and bacterial invasion was tested using the gentamicin survival technique.

RESULTS

Closed-eye tears bound significantly more bacteria than open-eye tears. Fractionation of reflex tears showed that 11 out of the 13 fractions bound bacteria, while all 13 fractions significantly reduced bacterial invasion of corneal epithelial cells. Surprisingly, the SG/mucin component of closed-eye tears resisted bacterial binding and had no significant effect on bacterial invasion.

CONCLUSIONS

P. aeruginosa bacteria bind more efficiently to closed-eye tears than to open-eye tears. The mechanism by which tears bind bacteria and protect against invasion does not require SG/mucin, as this fraction of closed-eye tears does not contain either activity.

Inflammatory responses of corneal epithelial cells to Pseudomonas aeruginosa infection

PURPOSE

We hypothesized that corneal epithelium plays a role in the innate immune response by sensing the presence of pathogens and providing signals that activate the corneal defense system. We sought to determine the mechanisms involved in the activation of the signaling pathways and subsequent production of proinflammatory cytokines in human corneal epithelial cells (HCECs) in response to Pseudomonas aeruginosa infection.

METHODS

Epithelial monolayers of a telomerase-immortalized HCEC line, HUCL, and primary cultures of HCECs were exposed to P. aeruginosa (PA01 strain) with or without the presence of the NF-kappaB inhibitor kamebakaurin, the p38 inhibitor SB203580, or the JNK inhibitor SP600125. IkappaB-alpha phosphorylation and degradation and p38 and JNK phosphorylation were assessed at different time points by Western blot analysis. Interleukin (IL)-6, IL-8, and TNF-alpha levels were determined by reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA).

RESULTS

Exposure of HUCL cells and primary HCECs to P. aeruginosa resulted in rapid activation of NF-kappaB as indicated by an increase in IkappaB-alpha phosphorylation observed within 15 min and by IkappaB-alpha degradation, which peaked in 1 hr. Two stress-activated mitogen-activated protein kinases, p38 and JNK, were also activated as their phosphorylation was induced by P. aeruginosa infection. Concomitant with the activation of these Toll-like receptor-mediated signaling pathways, transcriptional expression and subsequent secretion of IL-6 and IL-8 in HUCL cells were also induced by P. aeruginosa. Presence of the NF-kappaB inhibitor kamebakaurin in culture medium blocked P. aeruginosa-induced NF-kappaB activation and inhibited IL-6, IL-8, and TNF-alpha expression and secretion. Inhibition of p38 or JNK also resulted in a decrease in bacteria-induced expression and secretion of these cytokines.

CONCLUSIONS

P. aeruginosa triggers an innate immune response in HCECs, and NF-kappaB and, to a lesser extent, the p38/JNK signal pathways are responsible for P. aeruginosa-induced proinflammatory cytokine production in these cells.

Internalization of Pseudomonas aeruginosa is mediated by lipid rafts in contact lens-wearing rabbit and cultured human corneal epithelial cells

PURPOSE

The internalization of Pseudomonas aeruginosa (PA) in nasal and tracheal epithelium has recently been shown to involve the formation of cholesterol- and sphingolipid-rich plasma membrane domains (lipid rafts). The purpose of this study was to investigate the role of lipid rafts in PA internalization by corneal epithelium in vivo, in vitro, and after contact lens wear.

METHODS

Lipid raft formation was evaluated in rabbit corneas with and without contact lens wear and a human corneal epithelial (hTCEpi) cell line before and after PA infection with cornea-pathogenic strains by staining with FITC-conjugated cholera toxin beta-subunit, known to bind the lipid raft component GM1. Bacterial internalization was assessed by gentamicin survival assay. The role of lipid rafts in PA internalization was evaluated by pretreatment of hTCEpi cells with cholesterol metabolism inhibitors. The interaction of PA with lipid rafts was confirmed by flow cytometry.

RESULTS

Contact lens wear in rabbits induced lipid raft formation in occasional surface corneal epithelial cells. Subsequent PA exposure showed preferential binding to lipid raft-forming cells, leading to lipid raft aggregation and PA internalization. A similar sequence of lipid raft formation and PA internalization was also observed in hTCEpi for all PA strains. Internalization of all PA strains was blocked by three cholesterol metabolism inhibitors (P < 0.01). Flow cytometry showed an association of PA with rafts.

CONCLUSIONS

These findings demonstrate that contact-lens-mediated PA internalization involves lipid raft formation. Also, hTCEpi cells may be used as an experimental model for studying further the molecular mechanism(s) of PA infection in the corneal epithelium.

Non-steroidal anti inflammatory agents decrease bacterial colonisation of contact lenses and prevent adhesion to human corneal epithelial cells

PURPOSE

To investigate non-steroidal anti-inflammatory agents (NSAIDs), salicylic acid, sodium diclofenac and ketorolac for inhibition of bacterial colonization of contact lenses (CL) and human corneal epithelial cells (HCE).

METHODS

CLs pre-colonised with Pseudomonas aeruginosa, Haemophilus influenzae, Staphylococcus epidermidis and Streptococcus pneumoniae were exposed overnight to NSAIDs and the number of viable bacteria on the CLs were calculated. Cytotoxicity of NSAIDs to HCE cells was evaluated with the MTT assay. Viable counts were used to measure the adhesion of P. aeruginosa and S. epidermidis to HCE cells in the presence of the least cytotoxic NSAID.

RESULTS

All NSAIDs significantly decreased bacterial colonization of CLs in a dose-dependent manner. Salicylic acid (100 mM) completely inhibited colonisation of all species tested and was the least cytotoxic. Salicylic acid also prevented adhesion of P. aeruginosa and S. epidermidis to HCE (60% and 58% inhibition at 60 mM at 2 hours).

CONCLUSIONS

Salicylic acid demonstrated potential as a compound for incorporation into anti-bacterial strategies to prevent bacterial contamination of contact lenses. This study highlighted the potential for NSAIDs as anti-bacterial agents and indicates that this class of compound should be investigated for other suitable candidates.

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

PURPOSE

During contact lens wear, bacterial contamination of the lens can lead to the development of microbial keratitis (MK) or contact lens induced acute red eye (CLARE). Inflammatory mediators released by the host may heighten the response. We have examined the ability of human corneal epithelial cells and polymorphonuclear leukocytes (PMNs) to release cytokines upon stimulation with bacteria.

METHODS

Serratia marcescens strains were added to corneal epithelial cells or PMNs. After incubations of up to 20 hours, supernatants were assayed for the presence of inflammatory mediators by ELISA.

RESULTS

All strains stimulated PMNs to release IL-8 and LTB(4). Epithelial cells did not release LTB(4). IL-8 was released after exposure to most S. marcescens isolates. A sub-group of strains stimulated the release of TNF-alpha from corneal epithelial cells.

CONCLUSIONS

S. marcescens can stimulate the release of inflammatory mediators from both PMNs and corneal epithelial cells. This release could be important in the progression and resolution of MK and CLARE.

Polyphosphate kinase 1 and the ocular virulence of Pseudomonas aeruginosa

PURPOSE

To determine the role of polyphosphate kinase 1 (PPK1) in the ocular virulence of Pseudomonas aeruginosa.

METHODS

Using a mouse model of infection, P. aeruginosa strains PAO1, PAOM5 (an isogenic mutant of PAO1 deficient in PPK1), and PAOM5+PPK1 (the mutant complemented with PPK1 on plasmid pHEPAK11) were compared for ocular virulence. These strains were also characterized with respect to traits associated with survival and pathogenicity in an ocular environment.

RESULTS

The PPK1-deficient strain PAOM5 was significantly less virulent than either wild-type PAO1 or the complemented mutant (P <0.016). Loss of virulence was not associated with serum sensitivity or diminished adherence to the cornea. However, PAOM5 has an increased susceptibility to oxidative stress and was cleared from corneal tissue significantly better (P <0.006) than either the wild-type or restored strain. Furthermore, the PPK1-deficient mutant produced significantly less (P <0.022) pyocyanin.

CONCLUSIONS

PPK1 is essential for a successful ocular infection by P. aeruginosa. The loss of ocular virulence is probably due to the dysregulation of multiple genes, including those responsible for stress response.

Hypoxia increases corneal cell expression of CFTR leading to increased Pseudomonas aeruginosa binding, internalization, and initiation of inflammation

PURPOSE

To investigate the effect of hypoxia-induced molecular responses of corneal epithelial cells on the surface of rabbit and human corneas and corneal cells in culture on interactions with Pseudomonas aeruginosa that may underlie increased susceptibility to keratitis.

METHODS

Organ cultures of rabbit and human corneal tissue, primary rabbit and human corneal cells, and transformed human corneal cells from a patient with cystic fibrosis and the same cell line corrected for expression of wild-type cystic fibrosis transmembrane conductance regulator (CFTR), the cellular receptor for P. aeruginosa, were exposed to hypoxic conditions for 24 to 72 hours. Changes in binding and internalization of P. aeruginosa were measured using cellular association and gentamicin-exclusion assays, and expression of CFTR and activation of NF-kappaB in response to hypoxia were determined by confocal laser microscopy and quantitative measurements of NF-kappaB activation.

RESULTS

Hypoxia induced in a time- and oxygen-concentration-dependent manner increased association and internalization of clinical isolates of P. aeruginosa in all cells tested. Hypoxia increased CFTR expression and NF-kappaB nuclear translocation in rabbit and human cells with wild-type CFTR. Corneal cells lacking CFTR had reduced NF-kappaB activation in response to hypoxia. Hypoxia did not affect the increase in corneal cell CFTR levels or NF-kappaB activation after P. aeruginosa infection.

CONCLUSIONS

Hypoxic conditions on the cornea exacerbate the binding and internalization of P. aeruginosa due to increased levels of CFTR expression and also induce basal NF-kappaB activation. Both of these responses probably exacerbate the effects of P. aeruginosa infection by allowing lower infectious doses of bacteria to induce disease and promote destructive inflammatory responses.

Pseudomonas aeruginosa corneal binding after 24-hour orthokeratology lens wear

PURPOSE

To examine the effect of short-term 24-hr orthokeratology lens (OKL) wear on Pseudomonas aeruginosa binding, epithelial surface cell morphology, epithelial sheet thickness, and stromal thickness in a rabbit model.

METHODS

Seventeen New Zealand white rabbits were treated according to the Association for Research in Vision and Ophthalmology Statement for the Use of Animals in Ophthalmic and Vision Research. Partial membranectomy was performed on all rabbits 1 week before the experiments. Baseline values for epithelial and stromal thickness and epithelial surface cell size were determined by in vivo confocal microscopy in one randomly chosen eye (n = 6). One week later, rabbits were fitted in the same eye with a hyper oxygen-transmissible OKL. Twenty-four hours later, confocal microscopy was repeated. The second group of rabbits (n = 6) was fitted with an OKL in one randomly chosen eye for 24 hr. P. aeruginosa binding to the corneal epithelium was assessed for the control corneas and those exposed to the test lens. Scanning electron microscopy was performed on a third group of rabbits to assess epithelial surface damage (n = 5).

RESULTS

There was a statistically significant difference (P<0.001) in P. aeruginosa binding between the control (1.11 +/- 0.74 x 10(5) colony-forming units per cornea) and the OKL-wearing eyes (2.74 +/- 0.69 x 10(5) colony-forming units per cornea). The central epithelium thinned by 6.5% after lens wear (48.2 +/- 1.9 microm to 45 +/- 1.7 microm, P=0.005); however, central stromal thickness increased by 7.3% (322 +/- 22 microm to 345 +/- 29 microm, P=0.006). Compared with the baseline value, central epithelial cell size increased significantly from 1,253 +/- 140 mm(2) to 1,627 +/- 393 mm(2) (29.4%, P=0.02). Scanning electron microscopy showed increased surface epithelial damage associated with OKL wear.

CONCLUSIONS

This prospective, masked, pilot study showed that 24-hr hyper oxygen-transmissible OKL wear induced a statistically significant increase in P. aeruginosa binding to the epithelium of the rabbit cornea, accompanied by central epithelial thinning, stromal thickening, and surface cell damage assessed by scanning electron microscopy. Collectively, the data suggest that despite adequate lens oxygen transmissibility, the mechanical pressure inherent in the OKL design exerted on the corneal surface appears to be associated with increased adherence of P. aeruginosa to surface corneal epithelial cells, which may pose an increased risk for lens-related microbial keratitis, especially in overnight (i.e., closed-eye) wearing conditions. Future studies are needed to determine whether these results are similar in human wear and how P. aeruginosa binding during OKL wear compares with other lens-wearing modalities, such as daily or continuous soft lens wear.

Innate immune response of corneal epithelial cells to Staphylococcus aureus infection: role of peptidoglycan in stimulating proinflammatory cytokine secretion

PURPOSE

This study sought to elucidate the innate immune responses of cultured human corneal epithelial cells (HCECs) to infection by the Gram-positive bacterium Staphylococcus aureus and to determine the underlying mechanisms.

METHODS

HUCL, a telomerase-immortalized HCEC line, and primary cultures of HCECs were challenged with live or heat-killed S. aureus, its exoproducts, or cell wall components lipoteichoic acid (LTA) and peptidoglycan (PGN). IkappaB-alpha phosphorylation and degradation as well as phosphorylation of MAPKs, p38, and JNK-1/2, were assessed by Western blot analysis. The expression of interleukin (IL)-6, IL-8, TNF-alpha, and beta-defensin-2 were determined using RT-PCR and secretion of IL-6, IL-8, TNF-alpha, and beta-defensin were measured using enzyme-linked immunosorbent assay and immunoblot analysis of culture medium.

RESULTS

Exposure of HUCL cells to live, but not heat-killed, S. aureus resulted in NF-kappaB activation in a time-dependent manner, as assessed by the increase in IkappaB-alpha phosphorylation and degradation. Live bacteria also activated the p38 and JNK pathways. The effects of live bacteria on HUCL cells may be attributable to bacterial exoproducts, since the conditioned medium of S. aureus also effectively stimulated these signaling pathways. PGN, but not LTA, activated the NF-kappaB and MAPK pathways in a dose- and time-dependent manner. Concomitant with activation of NF-kappaB and MAPKs, transcriptional expression of IL-6, IL-8, TNF-alpha, and beta-defensin-2 were induced in cells challenged with bacterial exoproducts and PGN. Secretion of IL-6, IL-8, TNF-alpha, and beta-defensin-2 were also significantly increased in HCECs in response to bacterial exoproducts and PGN challenge.

CONCLUSIONS

Corneal epithelial cells possess the ability to recognize the presence of Gram-positive bacteria and to initiate the innate immune responses by the expression and/or release of proinflammatory cytokines and beta-defensin-2 in the cornea.

Role of EGFR transactivation in preventing apoptosis in Pseudomonas aeruginosa-infected human corneal epithelial cells

PURPOSE

To determine the role of epidermal growth factor (EGF) receptor (EGFR)-mediated signaling pathways in preventing infection-induced apoptosis in human corneal epithelial cells (HCECs).

METHODS

Epithelial monolayers of a telomerase-immortalized HCEC line, HUCL, and primary culture of HCECs were infected with Pseudomonas aeruginosa in the presence of the EGFR inhibitor tyrphostin AG1478, the extracellular signal-regulated kinase (ERK) inhibitor U0126, the phosphoinositide 3-kinase (PI3K) inhibitor LY294002, the heparin-binding EGF-like growth factor (HB-EGF) antagonist CRM197, the HB-EGF neutralizing antibody, or the matrix metalloproteinase inhibitor GM6001. The activation of EGFR was analyzed by immunoprecipitation using EGFR antibodies, followed by Western blot analysis with phosphotyrosine antibody. Phosphorylation of ERK and Akt, a major substrate of PI3K, and generation of cleaved caspase-3 and poly (ADP-ribose) polymerase (PARP) were determined by Western blot analysis. Apoptotic cells were characterized by positive staining of active caspase-3, loss of mitochondrial cytochrome c, and condensation of chromosomes. Apoptosis was also confirmed by measuring caspase-3 activity and assessing the generation of cleaved caspase-3 and PARP.

RESULTS

P. aeruginosa infection of HUCL cells resulted in EGFR activation and EGFR-dependent ERK1/2 and PI3K phosphorylation. Inhibition of EGFR, ERK1/2, and PI3K activities with kinase-specific inhibitors (AG1478, U0126, and LY294002, respectively) resulted in an increase in the number of apoptotic cells, in elevated cellular caspase-3 activity, and/or in increased cleaved PARP in P. aeruginosa-infected HUCL cells or primary culture of HCECs. Blocking HB-EGF ectodomain shedding by inhibition of matrix metalloproteinase-mediated proteolysis, downregulation of HB-EGF, or neutralization of its activity retarded infection-induced EGFR transactivation and, as a consequence, increased infection-induced HUCL apoptosis.

CONCLUSIONS

Bacterial infection of HCECs induces EGFR transactivation through HB-EGF ectodomain shedding. EGFR and its downstream ERK and PI3K signaling pathways play a role in preventing epithelial apoptosis in the early stage of bacterial infection.

Role of Pseudomonas aeruginosa ExsA in penetration through corneal epithelium in a novel in vivo model

PURPOSE

The scarified cornea keratitis model was modified to study Pseudomonas aeruginosa infection of healing corneal epithelium. The new model was then used to study the role of ExsA, a transcriptional activator of P. aeruginosa, in bacterial penetration through injured and healing corneal epithelia.

METHODS

Scratch-injured corneas of C57BL/6 mice were allowed to heal for 0, 6, 9, or 12 hours before inoculation with a cytotoxic (6206) or invasive (PAO1) P. aeruginosa strain. Disease progression was monitored for 14 days. The integrity of the healing epithelium was studied in uninfected eyes by fluorescein staining and by histologic examination. In other experiments, the effect of bacterial exsA mutation was studied after 0, 6, or 12 hours of healing. Three hours after infection, these eyes were used to quantify early bacterial colonization levels by viable counts, or they were sectioned to study bacterial penetration through the epithelium by microscopy.

RESULTS

Corneas remained susceptible to infection 6 but not 12 hours after scratch injury. By 6 hours, the previously exposed stroma was already completely covered by several layers of epithelial cells. Fluorescein staining unexpectedly occurred even after 12 hours of healing time, showing that resistance to infection preceded full restoration of epithelial barrier function. Mutation of exsA reduced both bacterial colonization levels and penetration through the epithelium 3 hours after bacterial inoculation, but only in the 6-hour healing situation, and only for the cytotoxic strain (PA103). Mutation of exsA in the invasive strain (PAO1) had no effect on 3-hour colonization or penetration levels under any circumstances.

CONCLUSIONS

The 6-hour healing infection model showed a role for ExsA in early interactions with the corneal epithelium that was not detectable with the conventional (0-hour) scratch model. Comparison of the 6- and 12-hour healing models, which showed that factors additional to barrier function contribute to defense against infection, could be used to gain new insights into corneal defense mechanisms, and the methods used by bacteria to circumvent them.

[Infection immunology in silicone hydrogel contact lenses for continuous wear--a review]

BACKGROUND

The patient's wish for permanent refractive solution and optimal comfort must be weighed against the risk of infections. In order to meet these wishes and the demand for minimising associated risks, hyperoxygen-transmissible silicone hydrogel contact lenses have been developed.

METHODS

Colonisation and sensitivity to antibiotics of bacteria in vitro, expression of bacterial ligands of the corneal epithelium (rabbit model), and the morphology of complications in patients have been reported to characterise HOTL.

RESULTS

Bacterial adherence to hydrophobic silicone elastomers is low. The reduction of sensitivity towards antibiotics is higher for PMMA-adherent bacteria with respect to the conventional antibiotics compared to the silicone-elastomer adherent bacteria. Colonising bacteria are not significantly different in asymptomatic CL wearers concerning CFU and species: asymptomatic: CNS (54 vs. 47 %), propioni- (43 vs. 48 %), coryne- (6 vs. 10 %) and gram-negative bacteria (2 vs. 3 %), S. aureus (2 vs. 1 %), and in patients with keratitis are not significantly different concerning species: CLARE (H. influenzae, S. pneumoniae), CLPU (S. aureus, S. pneumoniae), IK (P. aeruginosa), however, concerning the CFU (gram-negative) 23.7 % (keratitis) vs. 3.8 %, (asymptomatic), S. pneumoniae 7.6 % vs. 0.6 %. The epithelial expression of bacterial ligands like WGA is lower for HOTL (3230 p/750 micro) than for low oxygen-transmissible (4611 p/750 micro) consistent with a decreased adherence of pseudomonas of 5.31 - 5.98 vs. 5.9 - 7.81 bacteria/cell. Asymptomatic morphological anomalies and keratitis are less frequent in HOTL. Apoptosis-induced desquamation and the central epithelial thickness decreased. In a one-year study of 504 patients wearing continuous wear HOTL for 30 days, corneal staining was seen in 10.6 vs. 10.5 % 30-day 7 day extended wear, infiltrates in 2.3 vs. 4.6 %, epithelial oedema in 3.6 vs. 2.0 % und tarsal conjunctival anomalies in 3.0 vs. 1.6 %. Individual reports on infectious keratitis in HOTL wearers have been published.

CONCLUSIONS

Fewer morphological anomalies and a decreased incidence of infections (on the basis of duration of wear) can be associated with the higher oxygen transmission of HOTL. From the clinical point of view, colonisation of HOTL with the same bacterial species as in conventional biomaterials, and the extended wear demand clear patient counseling and vigilant follow-up by an ophthalmologist.

Contact lens infections: can they ever be eradicated?

Since their introduction, the most significant complication of wearing soft contact lenses has been the development of vision-threatening microbial keratitis. In lens-wearing corneas, microbial infection is thought to develop in the absence of overt injury, leading to the hypothesis that microbe interactions with the corneal epithelium are critical to the pathogenesis of this disease. Thus, we have focused our research efforts on understanding microbial virulence mechanisms aimed at corneal epithelial cells and the innate defenses that normally protect them using the gram-negative bacterium Pseudomonas aeruginosa as a model organism. This report summarizes those results and explores their relevance to understanding contact lens-related infections.

Effects of daily and overnight wear of hyper-oxygen transmissible rigid and silicone hydrogel lenses on bacterial binding to the corneal epithelium: 13-month clinical trials

PURPOSE

For 14 years, the U. S. Food and Drug Administration (FDA) and eye care practitioners have strongly discouraged patients from sleeping in contact lenses. In the past 9 months however, the FDA has approved three new hyper-oxygen transmissible lenses for up to 30-night extended wear. Is this a great advance or another clinical triumph of hope over experience? What should the public know? What should patients do?

METHODS

Our research group has studied all three new lenses in prospective, randomized, masked, parallel clinical trials in a single center. As an outcome measure, we looked at whether lens wear caused more bacterial binding to surface corneal cells.

RESULTS

Compared with conventional lens use, the new lenses caused no or only small increases in bacterial binding in either daily or extended wear. Furthermore, the increases seen stratified with known infection risks by both lens type (hard or soft) and wearing schedule. Indeed, early epidemiologic reports indicate that this new generation of lenses may reduce lens-related microbial infection risks by 10- to 40-fold.

CONCLUSION

This represents a true clinical paradigm shift of the first magnitude in safety of contact lens wear. Taken together, this data suggest that patients will soon replace their current, conventional lenses with this new generation of materials for any schedule of wear.

Effects of contact lens care solutions on surface exfoliation and bacterial binding to corneal epithelial cells

PURPOSE

The purpose of this study is to assess the effects of commercially available contact lens wetting solutions on bacterial binding and cell exfoliation rates in human corneal epithelium.

METHODS

The effects of four contact lens care solutions were tested: ReNu Multi Plus (Bausch & Lomb, Rochester, NY) multipurpose solution; OPTI-FREE Express (Alcon, Ft. Worth, TX) multipurpose solution; Complete Blink-N-Clean (Allergan, Irvine, CA) lens drops; and Lens Plus (Allergan) rewetting drops.

STUDY DESIGN

Prospective, double-masked, randomized crossover clinical trial (N = 20 subjects).

OUTCOME MEASURES

Measures of outcome included binding of Pseudomonas aeruginosa (PA) to exfoliated corneal epithelial cells, and the rate of surface cell exfoliation. Cells were collected at the baseline (pretreatment) examination and 4 days later, after subjects used the assigned solution six times daily and once again immediately before cell collection (posttreatment). Following cell collection, patients underwent 1 week of recovery, during which no drops were used, and random cross-over assignment to the next test solution.

RESULTS

Use of test solutions increased PA binding, with a range of + 11.9% to + 58.2%. Analyzed together, PA binding increased significantly (+ 29%; P = 0.02, paired t-test); Lens Plus solution alone raised PA binding levels significantly (P = 0.022, 2-way ANOVA, Student-Newman-Keuls [SNK] test). Exfoliation rates were decreased from -7% to -52.7%. Analyzed together, cell exfoliation decreased significantly (P = 0.004; Wilcoxon signed rank test). Individual use of OPTI-FREE decreased exfoliation significantly (P = 0.019: 2-way ANOVA, SNK test).

CONCLUSIONS

Topical application of common commercial contact lens care solutions increases PA binding and reduces corneal surface cell exfoliation. Similar effects have also been reported with contact lens wear. Taken together, the data suggest that the use of lens solution itself may play a role in increasing PA binding to corneal epithelial cells and, hence, might potentially contribute inadvertently to increased risk for lens-related microbial keratitis.

The causes of and cures for contact lens-induced peripheral ulcer

PURPOSE

Contact lens-induced peripheral ulceration (CLPU) is a relatively common adverse response associated with wearing hydrogel lenses, especially on an extended wear schedule. Bacteriologic examination of lenses at the time of an event has demonstrated an association with Staphylococci spp. We sought to investigate the causes of CLPU in a rabbit model of contact lens wear.

METHODS

Rabbits wore contact lenses for a period of 24 hr in the presence or absence of bacteria or in presence or absence of epithelial scratches made in the periphery of the cornea before lens wear. Bacteria tested were a strain of Staphylococcus aureus or a strain of Staphylococcus epidermidis isolated from human CLPUs. Rabbits were also challenged with S. aureus in the presence of an epithelial defect and in the absence of a contact lens. Corneas were monitored by slitlamp, histology, and microbial culture after 24 hr.

RESULTS

No CLPU-like lesions were detected under the following conditions: corneal scratch plus lens wear with no bacteria; corneal scratch plus S. epidermidis colonized lenses; corneal scratch without lens wear and with S. aureus applied to eyes; no scratch plus S. aureus colonized lenses; and corneal scratch plus contact lenses colonized by dead S. aureus. CLPU-like lesions were found only when the corneas were scratched and contact lenses colonized by viable S. aureus were applied to the eye. The histology of the lesions demonstrated a frank epithelial break with underlying stromal infiltration. Only low numbers of bacteria could be cultivated from the corneas with CLPU-like lesions. The CLPU-like lesions shared many similarities with CLPU in humans.

CONCLUSION

CLPU-like lesions were only produced by S. aureus and not S. epidermidis in the presence of an epithelial abrasion and contact lens. Thus, we hypothesize that to reduce the incidence of CLPU, contact lenses designed to reduce corneal interaction and repel microbial colonization should be produced.

Pseudomonas aeruginosa binds to extracellular matrix deposited by human corneal epithelial cells

PURPOSE

To measure the effect of extracellular matrix substrate, pH, and O(2) on Pseudomonas aeruginosa binding.

METHODS

Extracellular matrix substrates were prepared from human corneal epithelial cells cultured in 2% or 20% O(2). P. aeruginosa strains ATCC 19660 or PAO1 (suspended in pH 7.0 or 7.5 buffer) were cultured on extracellular matrix substrates in 2% or 20% O(2). The mean number of adherent bacteria per counted per field +/- SEM (n = 15) was determined for combinations of bacteria, extracellular matrix substrate, pH, and O(2). Binding in the presence of antibodies directed against laminin-5 was also measured.

RESULTS

Extracellular matrix substrates produced by cells cultured in 20% O(2), combined with an environment of pH 7.0, provided the least favorable conditions for binding of strain 19660. In contrast, extracellular matrix substrates produced by cells cultured in 2% O(2), combined with an environment of pH 7.0, provided the most favorable conditions for binding of strain 19660. Binding of PAO1, however, as a function of extracellular matrix substrate and pH, did not similarly compare with binding of strain 19660. Antibodies against laminin-5 chains served to increase the number of strain 19660 bacteria bound to extracellular matrix substrates compared with the control.

CONCLUSIONS

The extracellular matrix secreted by hypoxic corneal epithelial cells is a substrate for binding of P. aeruginosa. Results in previous studies have shown that hypoxic extracellular matrix contains less laminin-5 protein than normoxic matrix. The antibody studies in this report suggest that the decrease in laminin-5 content in hypoxic matrix, relative to matrix secreted by normoxic corneal epithelium, may be responsible for increased bacterial adhesion.

Pseudomonas aeruginosa strains with lipopolysaccharide defects exhibit reduced intracellular viability after invasion of corneal epithelial cells

Pseudomonas aeruginosa is a leading cause of infectious keratitis. Many ocular isolates of this bacterium invade corneal epithelial cells in vitro and in vivo. Antibiotic survival assays have shown that a complete core lipopolysaccharide is required for full epithelial invasion by P. aeruginosa. In this study, we show that P. aeruginosa mutants with defects in their lipopolysaccharide core and O antigen exhibited reduced viability after internalization by corneal epithelial cells. Restoration of lipopolysaccharide core and O antigen expression by complementation with the plasmid pLPS1 restored intracellular survival. P. aeruginosa strains with a complete lipopolysaccharide survived and replicated within the cells. The data suggest that lipopolysaccharide is involved in the intracellular survival and/or replication of P. aeruginosa, indicating an additional mechanism by which this important virulence factor may contribute to the pathogenesis of corneal infection.

Effects of daily and overnight wear of a novel hyper oxygen-transmissible soft contact lens on bacterial binding and corneal epithelium: a 13-month clinical trial

OBJECTIVE

To test prospectively a new biologic rationale for an advanced hyper oxygen-transmissible lens (HOTL) providing prospects for safer daily (DW) or extended (EW) contact lens wear.

DESIGN

Prospective, randomized, double-masked, single-center, 13-month clinical trial.

PARTICIPANTS

One hundred sixty-eight patients completed the DW study (1 month): control lens (n = 70); HOTL (n = 98). One hundred thirty-six patients finished 1 year of EW: controls (n = 56), HOTL (n = 25, 6 nights; n = 55, 30 nights).

TESTING

Irrigation chamber to collect corneal surface cells, confocal microscopy, tear collection at baseline, 2, and 4, weeks of DW, and 24 hours, 1, 3, 6, 9, and 12 months of EW.

MAIN OUTCOME MEASURES

(1) Pseudomonas aeruginosa (PA) binding to exfoliated corneal surface cells; (2) central epithelial thickness (CET); (3) superficial cell area (SCA); (4) epithelial surface cell exfoliation (DESQ); and (5) tear lactate dehydrogenase (LDH).

RESULTS

Daily wear with control lens increased PA binding from 5.90 +/- 2.60 to 7.81 +/- 3.04 bacteria per cell (P < 0.01); HOTL wear increased PA binding significantly less (5.31 +/- 1.87-5.98 +/- 2.26; P < 0.01). Daily wear produced no significant changes in CET or SCA. Significant decreases in DESQ were seen with both lenses with no significant intergroup differences. Tear LDH increased significantly in DW with HOTL wear versus control (P = 0.0017), but not after 1 month of subsequent EW (P = 0.533). One to 3 months of EW with control lens showed significantly higher PA binding than HOTL wear (P < 0.01); binding adaptively decreased thereafter, returning to baseline at 9 to 12 months. Lens EW produced significantly enlarged SCA, thinning of CET (except 6-night HOTL wear), and decreased DESQ (P < 0.01). Some adaptive recovery was seen with CET and DESQ, but not SCA; importantly, the data indicated no significant difference between 6- or 30-night EW for all outcomes.

CONCLUSIONS

Hyper oxygen-transmissible lens wear (DW or EW) produced significantly decreased PA binding compared with control lens wear, with no significant difference in wearing schedule (6 nights vs. 30 nights); additionally, there was a remarkable and unexpected adaptive recovery in the first 6 months of all soft lens wear, with a return to baseline PA binding levels and partial recovery for the other outcomes except SCA at 1 year. These results suggest that HOTL use should result in a decrease in the incidence of and risk(s) for lens-related microbial keratitis and that further epidemiologic studies should consider time in adapted EW in future risk and incidence analyses.