Contact lens-related microbial keratitis: recent outbreaks

The Anti-Amoebic Activity of a Peptidomimetic against Acanthamoeba castellanii

Acanthamoeba is a free-living protozoan known to cause keratitis most commonly, especially among contact lens wearers. Treatment of Acanthamoeba keratitis is challenging as Acanthamoeba can encyst from the active form, a trophozoite, into a hibernating cyst that is refractory to antibiotics and difficult to kill; therefore, there is a need for more effective anti-amoebic strategies. In this study, we have evaluated the anti-amoebic activity of the antimicrobial peptide mimic RK-758 against Acanthamoeba castellanii. RK-758 peptidomimetic was subjected to biological assays to investigate its amoebicidal, amoebistatic, anti-encystation, and anti-excystation effects on A. castellanii. The anti-amoebic activity of the peptide mimic RK-758 was compared with chlorhexidine against the Acanthamoeba castellanii ATCC30868 and Acanthamoeba castellanii 044 (a clinical strain) with the concentrations of both ranging from 125 µM down to 7.81 µM. All experiments were performed in duplicate with three independent replicates. The data were represented as mean ± SE and analysed using a two-sample t-test and two-tailed distributions. A p < 0.05 was considered statistically significant. The peptidomimetic RK-758 had anti-Acanthamoeba activity against both trophozoites and cysts in a dose-dependent manner. The RK-758 had amoebicidal and growth inhibitory activities of ≥50% at a concentration between 125 µM and 15.6 µM against the trophozoites of both Acanthamoeba strains. Inhibitory effects on the cyst formation and trophozoite re-emergence from cysts were noted at similar concentrations. Chlorhexidine had 50% activity at 7.81 µM and above against the trophozoites and cysts of both strains. In the haemolysis assay, the RK-758 lysed horse RBCs at concentrations greater than 50 µM whereas lysis occurred at concentrations greater than 125 µM for the chlorhexidine. The peptidomimetic RK-758, therefore, has activity against both the trophozoite and cyst forms of Acanthamoeba and has the potential to be further developed as an anti-microbial agent against Acanthamoeba. RK-758 may also have use as an anti-amoebic disinfectant in contact lens solutions.

Clinical Comparison of Fusarium Keratitis according to the Initial Potassium Hydroxide (KOH) Smear: A Retrospective Study in South Korea

Purpose. This study aimed to compare predisposing factors, clinical characteristics, treatment, and prognosis of Fusarium keratitis according to the result of the initial potassium hydroxide (KOH) smear. Methods. This is a retrospective study of cases with Fusarium keratitis between January 2000 and December 2019 at two tertiary hospitals in South Korea. Patients were divided into two groups depending on the KOH smear result (KOH-positive and KOH-negative group), and its clinical factors were analyzed. Results. Among 319 fungal keratitis, seventy-nine cases were identified with Fusarium keratitis. Forty-seven cases (59.5%) were negative in the initial KOH smear prior to their diagnosis. The most common predisposing factor for Fusarium keratitis was ocular trauma (55.7%). There were no significant differences in sex, occupation, ulcer size or shape, hypopyon, and initial visual acuity between the two groups. Differences were observed between the KOH-positive group and the KOH-negative group in terms of deep corneal infiltration (50.0% vs. 78.7%, $p=0.008$ ) and evisceration treatment (3.1% vs. 25.5%, $p=0.008$ ). The delayed time to initiate antifungal eye drops was longer in the KOH-negative group (1.13 ± 0.49 vs. 3.93 ± 4.89, $p=0.002$ ). Only the KOH-negative group combined bacterial infection. The significant risk factors for poor clinical outcomes were the central corneal lesion (odds ratio (OR) 3.50, $p=0.047$ ), a large ulcer size (size ≥ 7.5 mm2) (OR 4.98, $p=0.009$ ), and endothelial plaque (OR 7.00, $p=0.031$ ). Conclusion. Initial KOH-negative patients often needed evisceration and had worse final visual outcomes. The delay of prompt initiation of antifungal treatment and combined bacterial infection result in a poor prognosis. This study highlights the initial KOH effect on early diagnosis and early treatment of Fusarium keratitis.

Antibacterial Activity of Antibiotic-Releasing Polydopamine-Coated Nephrite Composites for Application in Drug-Eluting Contact Lens

The aim of this study is to prepare ciprofloxacin (CIP) or levofloxacin (LEVO)-incorporated and polydopamine (PDA)-coated nephrite composites for application in drug-eluting contact lenses. PDA was coated onto the surface of nephrite to improve antibacterial activity and to payload antibiotics. CIP or LEVO was incorporated into the PDA layer on the surface of nephrite. Furthermore, CIP-incorporated/PDA-coated nephrite composites were embedded into the contact lenses. PDA-coated nephrite composites showed dull and smooth surfaces according to the dopamine concentration while nephrite itself has sharp surface morphology. CIP- or LEVO-loaded/PDA-coated nephrite composites also have dull and smooth surface properties. Nano and/or sub-micron clusters were observed in field emission-scanning electron microscopy (FE-SEM) observation, indicating that PDA nanoparticles were accumulated and coated onto the surface of nephrite. Furthermore, CIP- or LEVO-incorporated/PDA-coated nephrite composites showed the sustained release of CIP or LEVO in vitro and these properties contributed to the enhanced antibacterial activity of composites compared to nephrite or PDA-coated nephrite composites. CIP-incorporated/PDA-coated nephrite composites were embedded in the contact lenses and then, in an antibacterial study, they showed higher bactericidal effect against Staphylococcus aureus (S. aureus) compared to nephrite itself or PDA-coated nephrite composites. We suggest that CIP- or LEVO-loaded/PDA-coated nephrite composite-embedded contact lenses are a promising candidate for therapeutic application.

Differential Antimicrobial Efficacy of Preservative-Free Contact Lens Disinfection Systems against Common Ocular Pathogens

Microbial keratitis is a devastating disease that can cause eye damage and blindness and can be the result of infections by several common ocular pathogens. Importantly, some of these pathogens, such as Acanthamoeba, are particularly unsusceptible to biocides in common contact lens care solutions. Therefore, the disinfection efficacy of preservative-free (PF) disinfection systems against bacteria, fungi, and Acanthamoeba trophozoites and cysts should be assessed as products with the most potential to be efficacious against resistant organisms. PF disinfection systems were analyzed for antimicrobial efficacy. These were the one-step (hydrogen peroxide-based) Clear Care and Clear Care Plus systems and the two-step (povidone-iodine-based) Cleadew system. Stand-alone challenges using bacteria, fungi, and Acanthamoeba were prepared according to the International Standards Organization method 14729. These same challenges were also conducted in the presence of the following contact lenses: Boston RGP, Acuvue Oasys, Biofinity, Ultra, and 2-week PremiO. All challenges were performed at the manufacturer's recommended disinfection time. All preservative-free disinfection systems demonstrated similarly high rates of antimicrobial efficacy when challenged with bacteria or fungi, with or without lenses. However, both Clear Care and Clear Care Plus demonstrated significantly greater disinfection efficacy against Acanthamoeba trophozoites and cysts, with and without lenses (P < 0.05). Cleadew efficacy was impacted by the addition of contact lenses, whereas Clear Care/Clear Care Plus maintained similar efficacies in the absence or presence of lenses. While both hydrogen peroxide and povidone-iodine are highly effective against bacteria and fungi, hydrogen peroxide maintains significantly greater disinfection capabilities than povidone-iodine against all forms of Acanthamoeba. IMPORTANCE Understanding the most efficacious products will allow clinicians to best communicate to patients and consumers the safest products on the market to reduce adverse events, including microbial keratitis, during contact lens use.

Therapeutic Ultrasound-Enhanced Transcorneal PHMB Delivery In Vitro

OBJECTIVE

Delivery of therapeutic agents to the cornea is a difficult task in the treatment of parasitic keratitis. In this study, we looked at using different combinations of ultrasound parameters to enhance corneal permeability to polyhexamethylene biguanide (PHMB), a clinically available ophthalmic antiparasitic formulation.

METHODS

Permeability of PHMB was investigated in vitro using a standard diffusion cell setup. Continuous or 25% duty-cycle ultrasound was used at frequencies of 400 or 600 kHz, intensities of 0.5 or 0.8 W/cm² , and exposure times ranging from 1 to 5 minutes. Structural changes in the cornea were examined using light microscopy.

RESULTS

Ultrasound exposure produced increases in transcorneal delivery in every treatment parameter combination when compared to the sham treatment. The highest increase was 2.36 times for 5 minutes of continuous ultrasound at a frequency of 600 kHz and an intensity of 0.5 W/cm² with statistical significance (p <.001). Histological analysis showed that ultrasound application only caused structural changes in the corneal epithelium, with most damage being at the surface layers.

CONCLUSIONS

This study suggests the possibility of therapeutic ultrasound as a novel drug delivery technique for the treatment of parasitic keratitis. Further studies are needed to examine the thermal effects of these proposed ultrasound applications and the long-term viability of this treatment.

Genotype distribution of Acanthamoeba in keratitis: a systematic review

Acanthamoeba spp. are among the most worldwide prevalent protozoa. It is the causative agent of a disease known as Acanthamoeba keratitis, a painful and severe sight-threatening corneal infection that can lead to blindness. In recent years, the prevalence of Acanthamoeba keratitis has rapidly increased, growing its importance to human health. This systematic review aims to assess the distribution of Acanthamoeba sp. genotypes causing keratitis around the world, considering the sample collected type and the used identification method. Most of the cases were found in Asia and Europe. Not surprisingly, the T4 genotype was the most prevalent worldwide, followed by T3, T15, T11, and T5. Furthermore, the T4 genotype contains a higher number of species. Given the differences in pathology, susceptibility to treatment, and clinical outcome between distinct genotypes, it is essential to genotype isolates from Acanthamoeba keratitis cases to help to establish a better correlation between in vitro and in vivo activities, resulting in better drug therapies and successful treatment in cases of this important ocular infection.

Corneal Cross-linking as an Adjunct for The Management of Refractory Fungal Keratitis

PURPOSE:

To evaluate the effectiveness of ultraviolet (UV)-A/Riboflavin corneal cross-linking (CXL) for the treatment of the refractory cases of fungal keratitis.

METHODS:

In this prospective interventional study, 9 patients with the diagnosis of fungal keratitis that were referred to our emergency eye center were included. These patients were resistant to conventional treatment and underwent therapeutic UV-A/Riboflavin CXL. Response to the treatment was considered as good if rapid epithelialization and rapid decrease in stromal infiltration was occurred after PACK-CXL, and poor when the emergency transplantation was necessary to eradicate the infection.

RESULTS:

Nine patients treated with CXL due to recalcitrant fungal keratitis. Culture of the corneal scrapings showed Aspergillus species in 4 patients, Candida albicans in 1 patient and Fusarium species in the remainder of them. CXL was performed from 1 to 20 days after the presentation of corneal ulcers (Mean: 9.12 ± 4.02; range: 5–20 days). Postoperatively, the mean time to epithelialization was 14.25 ± 2.38 days, and mean time to resolution of stromal infiltration was 22.5 ± 7.29 days, in responsive cases. Four out of 9 eyes showed good response, and five patients showed no response, and corneal transplantation was performed to eradicate the infection. There was no statistically significant difference in mean depth of infiltration and mean size of ulcer between responsive and unresponsive patients (P = 0.86 and 0.08, respectively).

CONCLUSION:

Although UV-A/Riboflavin CXL is not a definite treatment for all of the fungal keratitis, it seems promising in the management of some refractory cases.

CLEAR - Evidence-based contact lens practice

Evidence-based contact lens -->practice involves finding, appraising and applying research findings as the basis for patient management decisions. These decisions should be informed by the strength of the research study designs that address the question, as well as by the experience of the practitioner and the preferences and environment of the patient. This reports reviews and summarises the published research evidence that is available to inform soft and rigid contact lens history and symptoms taking, anterior eye health examination (including the optimised use of ophthalmic dyes, grading scales, imaging techniques and lid eversion), considerations for contact lens selection (including the ocular surface measurements required to select the most appropriate lens parameter, lens modality and material selection), evaluation of lens fit, prescribing (teaching self-application and removal, adaptation, care regimen and cleaning instructions, as well as -->minimising risks of lens wear through encouraging compliance) and an aftercare routine.

The impact of patient behaviour and care system compliance on reusable soft contact lens complications

Reusable soft daily wear contact lenses (CLs) remain popular and were fit to just over half of all wearers in the most recent international CL prescribing survey. Unlike daily disposable CLs, reusables require cleaning and disinfecting after every use, along with storage in a CL case. These additional requirements add a number of steps to the daily wear and care routine, increasing the opportunities for CL wearers to exhibit non-compliant behaviour. The impact of non-compliance ranges from poor lens comfort through to potentially sight-threatening infective keratitis. The coronavirus pandemic has refocused the profession on the importance of hand hygiene in particular, and the need for promoting safe CL wear in general. This review summarises typical non-compliant behaviour related to reusable CLs, and examines strategies and opportunities to better support wearers. Patient education has a central role in encouraging compliant behaviour, although patient recall of information is low, and personal belief systems may result in continuation of non-compliant behaviour despite awareness of the risks. CL care solutions are required for the daily disinfection of lenses, however misuse of multipurpose solutions (MPS) and hydrogen peroxide (H₂O₂)-based care systems can challenge their ability to be fully efficacious. Standard efficacy testing is reviewed, with consideration of how well current protocols model real-world use of CL solutions. Although some recommendations are in place for the inclusion of additional variables such as lens cases, CL materials, organic soil and efficacy against Acanthamoeba, opportunity still exists to reevaluate global standards to ensure consistency of testing in all markets. Finally, potential future innovations are discussed which may further support increased safety in reusable lens wear through novel antimicrobial additions to both CL materials and cases.

Ultrasound-Enhanced Drug Delivery for Treatment of Acanthamoeba Keratitis

Reaching sufficient amounts of therapeutic agents in ocular tissues is a major challenge in ophthalmology. In this study, we examined the effects of ultrasound application for delivery of polyhexamethylene biguanide for treatment of Acanthamoeba keratitis. Ultrasound intensities of 0.5 - 0.8 W/cm² and frequencies of 400 - 600 kHz were tested with exposure durations of 1 - 5 minutes. Light microscopy was used to determine the ultrasound-induced structural changes in the cornea. All groups showed increases in drug concentration, up to 2.36 times, passing through the cornea, with the 600 kHz treatment groups reaching statistical significance. Structural changes were observed in the epithelial layer of the cornea, but the stroma and endothelium remained mostly unaffected.

Acanthamoeba keratitis related to contact lens use in a tertiary hospital in China

Background

To report the clinical and microbiological features of Acanthamoeba keratitis (AK) related to contact lens use in a tertiary hospital in China.

Methods

In this retrospective study, the medical results of 61 cases of AK related to contact lens use from January 2000 to December 2017 were reviewed. The data included patients’ demographics, lens type, history, risk factors, disease stages, corneal scraping and culture reports, and treatments. Moreover, genotypic identification of some of the isolates was carried out with a PCR assay and sequence analysis of the 18S ribosomal DNA gene.

Results

There were 64 eyes included in the study. A total of 32.8% of the patients wore soft contact lenses, and 67.2% of patients used overnight orthokeratology. In the cases (20 eyes) in the early stage, 65% (13 eyes) had positive results according to Giemsa-stained smears, and 0.9% sodium chloride (NaCl) wet mounts revealed trophozoites in 7 eyes (35%). Six eyes (30%) were diagnosed by confocal microscopy combined with clinical signs. In the orthokeratology patients, 87.8% (36/41) rinsed their lenses and/or cases with tap water; 55% of soft-lens wearers wore their lenses while showering. The genotype of 9 isolates was determined, and all the strains belonged to genotype T4. In the orthokeratology group, the number of patients who required therapeutic penetrating keratoplasty after 2005 was less than that before 2005 (chi-square test, χ² = 4.209, P = 0.04).

Conclusions

More than two-thirds of the cases were associated with orthokeratology. Examinations with Giemsa-stained smears, 0.9% NaCl wet mounts and confocal microscopy should be performed for patients who are highly suspected of having early-stage AK to help with early diagnosis. In the orthokeratology group, the rate of therapeutic keratoplasty after 2005 was less than that before 2005.

Electronic supplementary material

The online version of this article (10.1186/s12886-019-1210-2) contains supplementary material, which is available to authorized users.

The use of preservatives in dry eye drops

Topical ocular preparations are widely recommended by health care professionals, or chosen by patients, to help manage dry eye disease (DED). The chronic and progressive nature of DED may result in the administration of topical products several times a day, over a period of many years. Given DED is a condition that by definition affects the ocular surface, it is important to understand how the repeated use of eye drops may impact the ocular surface, influence clinical signs, affect symptoms, and impact the overall disease process of dry eye. The component in topical preparations with the greatest potential to adversely affect the ocular surface is the preservative. This paper reviews the literature in relation to the use of preservatives in formulations for dry eye. The ocular effects of benzalkonium chloride (BAK) are summarised and compared to the performance of alternative preservatives and preservative-free formulations. Use of preserved and preservative-free drops in relation to the management of varying stages of DED is discussed.

The effects of FK506 combined with natamycin in the treatment of experimental fungal keratitis by suppressing NLRP3 inflammasome activation

The aim of this study was to investigate the mechanisms of combination treatment with FK506 and natamycin on alleviating damage of the cornea in mouse model of fungal keratitis.

In this study, the mouse model of fungal keratitis was created by intrastromal injection with Fusarium solani or Aspergillus flavus. The mice received 5% natamycin eye drops 6–8 times a day, or the mice received 0.05% FK506 eye drops 2 times per day for 21 consecutive days. Corneal damage was evaluated by H&E staining. The protein expression levels of NLRP3 were detected by immunohistochemistry. Moreover, the markers of inflammasome activation including NLRP3, ASC, caspase-1, IL-1β, and IL-18 were detected by western blot.

Histopathological results showed increased corneal thickening, dense inflammatory cell infiltration, and loss of epithelial continuity in the corneas after fungal infection. In addition, NLRP3 positive signals were observed to be obviously increased in the corneas after A. flavus or F. solani infection compared to the control group. Furthermore, the NLRP3 inflammasome is induced by fungal infection, as evidenced by increased protein expression levels of NLRP3, ASC, caspase-1, and downstream cytokines, such as interleukin (IL)-1β and IL-18. However, the corneal damage was alleviated and the activation of the NLRP3 inflammasome was significantly inhibited by drug treatment. Besides, the treatment outcomes were better in combined treatment group than that in single-agent treatment group.

In conclusion, FK506 combined with natamycin alleviate fungi-induced corneal damage by suppressing NLRP3 inflammasome activation.

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.

Role of Pattern Recognition Receptors in the Modulation of Antimicrobial Peptide Expression in the Corneal Epithelial Innate Response to F. solani

Purpose

Fusarium solani (F. solani) keratitis is a potentially sight-threatening fungal infection of the cornea. Antimicrobial peptides (AMPs), such as human β-defensins (hBDs) and cathelicidins, essential components of the immune system, likely have a protective role against F. solani keratitis. We examined the role of pattern recognition receptors (PRRs), Dectin-1, and TLR2 in F. solani–induced modulation of AMP expression in vitro.

Methods

Human corneal epithelial cells (HCECs) were exposed to heat-inactivated F. solani or pathogen-associated molecular patterns (PAMPs) of F. solani (Zymosan or Zymosan Depleted) for 6, 12, or 24 hours following which AMP mRNA and protein levels were determined. Involvement of TLR2 and Dectin-1 was confirmed by using siRNA knock-down (TLR2 and Dectin-1) or chemical inhibitor BAY 61-3606 (Dectin-1). The functional significance of AMP upregulation was tested using culture supernatant from F. solani or PAMP-treated HCECs against F. solani in the presence of hBD2 or LL37 neutralizing antibody.

Results

We confirm that HCECs express Dectin-1 and TLR2. HCECs demonstrated upregulation of AMPs hBD2 and cathelicidin LL37 following exposure to heat-inactivated F. solani or PAMPs. TLR2 and Dectin-1 knockdown and BAY 61-3606 treatment decreased AMP mRNA upregulation confirming PRR involvement. The culture supernatant from F. solani or PAMP-treated HCECs showed substantial killing of F. solani and hBD2 or LL37 neutralizing antibody significantly decreased this effect implicating involvement of these AMPs.

Conclusions

These findings demonstrate that Dectin-1 and TLR2 have an important role in regulating F. solani-induced AMP expression in corneal epithelial cells.

Evaluation of loop-mediated isothermal amplification assay for rapid diagnosis of Acanthamoeba keratitis

BACKGROUND

The clinical features of Acanthamoeba keratitis (AK) are non-specific and closely resemble bacterial, viral and fungal keratitis.

MATERIALS AND METHODS

We compared loop-mediated isothermal amplification (LAMP) with microscopy, non-nutrient agar (NNA) culture and polymerase chain reaction (PCR) in clinical suspects of AK.

RESULTS

Of 52 clinical samples (42 AK suspects and 10 proven bacterial, viral or fungal keratitis), 3 were positive by direct microscopy (sensitivity 60%, confidence interval [CI]: 17%-92.7%), and 5 by NNA culture, 18S rDNA PCR and LAMP (sensitivity 100%, CI: 46.3%-100%). The limit of detection of Acanthamoeba DNA was 1 pg/μl by both LAMP and PCR.

CONCLUSION

PCR and LAMP assays targeting 18S rDNA gene were found particularly suitable for a rapid and accurate diagnosis of AK. LAMP assay takes 2-3 h lesser than PCR, and thus offers a rapid, highly sensitive and specific, simple and affordable diagnostic modality for patients suspected of AK, especially in resource limited settings.

Risk Factors for Contact Lens-Related Microbial Keratitis: A Case-Control Multicenter Study

PURPOSE

The most feared complication of contact lens (CL) wear is microbial keratitis (MK), even though its incidence remains low. This study aimed to identify the risk factors of CL-related MK in a large, prospective, multicenter case-control study.

METHODS

A multicenter case-control study was designed. The CL-related MK subpopulation (Case) was compared with healthy CL wearers (Control) using a 52-item anonymous questionnaire designed to determine subject demographics and lens wear history. Univariate and multivariate logistic regression analyses were performed to compare both groups.

RESULTS

The study enrolled 499 cases and 508 controls. The risk factors associated with the greatest increased odds of CL-related MK were as follows: using disinfecting solution more than 3 months (odds ratio [OR]=1.94), cosmetic CL wear and use of multipurpose disinfection solution (1.37 each), overnight wear, and soft lens use (OR=1.24 each). The protective factors associated with the greatest reduction in OR were fitting by an ophthalmologist (OR=0.73) and hyperopia versus myopia (OR=0.75).

CONCLUSIONS

The infectious determinants were linked to the type of lenses, hygiene routine, CL handling, disinfecting solution, and storage case. This study aimed to highlight the increasingly CL-related MK, which likely occurs because of lack of patient information regarding basic rules of hygiene and CL care and handling.

Emerging trends in contact lens-related infections

PURPOSE OF REVIEW

This article reviews the literature on past and recent trends in contact lens-related microbial keratitis from bacterial, fungal, and Acanthamoeba infections.

RECENT FINDINGS

Contact lens wear is the most important risk factor for microbial keratitis. Despite increased use of daily disposable contact lens wear, the incidence of bacterial ulcers related to contact lens wear remains high. Overnight contact lens wear is the leading risk factor in contact lens-related bacterial infections. There may be a trend towards increasing antibiotic resistance of Gram-positive bacteria to fourth-generation fluoroquinolones. The incidence of Acanthamoeba and fungal infections, despite resolution of two outbreaks involving multipurpose solutions, are also on the rise.

SUMMARY

Contact lens-related microbial keratitis is rising and may be associated with more severe, vision threatening, infections.

Microbiological profile of corneal ulcer cases diagnosed in a tertiary care ophthalmological institute in Nepal

Background

Corneal ulcer, a major cause of monocular blindness in developing countries has consistently been listed as the major cause of blindness and visual disability in many of the developing nations in Asia, Africa and the Middle East, ranking second only to cataract. This study was carried out to determine the microbiological profile of corneal ulcer cases diagnosed among patients visiting Tilganga Institute of Ophthalmology (TIO), Nepal.

Methods

A total of 101 corneal scrapping samples were tested for routine culture and antibiotic susceptibility at the pathology department of TIO Nepal from April to October 2014. Microorganisms were identified by using standard microbiological procedures following the manual of American Society for Microbiology (ASM) and their antibiotic susceptibility test, performed by Kirby-Bauer disc diffusion method in conformity with the CLSI guideline.

Results

Out of 101 samples analyzed, 44.6% (45/101) showed positive growth with bacterial isolates i.e., 56% (25/45), more prevalent than fungus i.e., 44% (20/45). Among bacteria Streptococcus pneumoniae (31.1%, N = 14) was isolated in highest number whereas Fusarium (13.4%, N = 6) was the most common fungus species. Pseudomonas aeruginosa was the only Gram negative bacteria isolated from corneal ulcer cases. All bacterial isolates were found to be susceptible to the quinolone group of antibiotics (moxifloxacin followed by ofloxacin and ciprofloxacin).

Conclusions

These findings showcase the current trend in the microbiological etiology of corneal ulcer in Nepal, which have important public health implications for the treatment as well as prevention of corneal ulceration in the developing world.

Amniotic Membrane Graft with Argon Laser Photocoagulation Versus Amniotic Membrane Graft with Tissue Debridement for Treatment of Mycotic Keratitis

AIM

To compare augmented therapy with argon laser and amniotic membrane graft (AMG) versus AMG and tissue debridement for resistant mycotic corneal ulcers.

METHODS

This study included 40 cases of resistant fungal corneal ulcers in two groups. In one group, argon laser photocoagulation and AMG were done while AMG with tissue debridement was done as adjunctive therapy for the specific antifungal agents.

RESULTS

Complete healing with no adverse effects was achieved in argon laser group in duration ranging from 2-3 weeks in all cases. In the AMG group, duration of healing ranged from 3-5 weeks. Visual acuity was improved with one or more line gain in eight cases (40%) in the laser group, while in six cases (30%) only in the AMG group.

CONCLUSIONS

Augmented therapy with argon laser and AMG is superior to AMG with tissue debridement for treatment of resistant fungal corneal ulcers.

Argon laser photocoagulation versus intrastromal voriconazole injection in treatment of mycotic keratitis

AIM

To compare argon laser photocoagulation and intrastromal injection of voriconazole as adjunctive treatment modalities in cases of resistant mycotic corneal ulcers.

METHODS

Two groups each of them included 20 cases of resistant mycotic corneal ulcers. Both groups treated with local and systemic specific antimicrobial drugs guided with culture and sensitivity results. In one group argon laser photocoagulation was used as an adjunctive therapy to the specific antifungal drugs and in the other group, intrastromal injection of voriconazole was done besides the specific antifungal drugs. The 40 cases included in the study were proven according to culture and sensitivity to be 28 cases with pure fungal results and 12 cases with mixed (fungal and bacterial). In argon laser group, argon laser irradiation of the corneal ulcer was performed using argon laser 532 nm wavelength (Carl Zeiss LSL 532s AG; Meditec, Inc.) after fluorescein staining. In the other group, voriconazole solution (500 µg/mL) was prepared and injected in the corneal stroma. All cases were followed up for 3mo after healing was achieved.

RESULTS

Complete healing of the epithelial defect and resolution of stromal infiltration with no adverse effects were achieved in argon laser group in duration ranged from 2-4wk in 90% of cases. In voriconazole group 4 cases needed amniotic membrane graft due to thinning and 16 cases healed in duration ranged from 2-6wk (80% of cases).

CONCLUSION

Argon laser photocoagulation is superior to intrastromal voriconazole injection in treatment of resistant fungal corneal ulcers.

Genotyping of Acanthamoeba spp. and characterization of the prevalent T4 type along with T10 and unassigned genotypes from amoebic keratitis patients in India

Free-living amoebae of the genus Acanthamoeba are the causative agents of severe sight-threatening infection of the cornea. This study was designed to characterize the genotype of 20 Acanthamoeba spp. isolates obtained from corneal scrapings of 183 suspected Acanthamoeba keratitis patients reporting to the Outpatient Department/Casualty Services of Dr R. P. Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India during the period 2011-2015. Corneal scrapings were inoculated onto 2 % non-nutrient agar plates overlaid with Escherichia coli and incubated at 30 °C for 15 days. Amongst 183 suspected Acanthamoeba keratitis patients, 29 were found culture-positive for Acanthamoeba spp. out of which 20 samples were established in axenic culture for molecular analysis. DNA was isolated and PCR assay was performed for the amplification of the diagnostic fragment 3 (DF3) (∼280 bp) region of the 18S rRNA gene from axenic culture of 20 Acanthamoeba spp. isolates. Rns genotyping was performed on the basis of variation in nucleotide sequences of the DF3 region of the 18S rRNA gene. In the phylogenetic analysis, 16 of the 20 isolates were found to be of prevalent genotype T4, two were of genotype T10 and the remaining two isolates were of unassigned genotypes. Hence, it was concluded that genotype T4 was found as the most predominant genotype involved in Acanthamoeba keratitis infections. Genotype T10, which had not been reported from India, was detected for the first time in two patients. Two isolates were found to be unique, which shared < 95 % homology with all the known genotypes (T1-T20) of Acanthamoeba spp.

Chitinase 3-Like 1 Promotes Candida albicans Killing and Preserves Corneal Structure and Function by Controlling Host Antifungal Responses

Chitinase 3-like 1 (CHI3L1) has been shown to play a role in promoting antibacterial responses, decreasing tissue injury, and enhancing pulmonary repair. This study sought to elucidate the role of CHI3L1 in augmenting the corneal innate immune response to Candida albicans infection in an animal model of fungal keratitis. Flagellin applied topically 24 h prior to C. albicans inoculation significantly protected the corneal from C. albicans and induced CHI3L1 expression in C57BL/6 mouse corneas. CHI3L1, however, played a detectable but minor role in flagellin-induced protection. While C. albicans keratitis was more severe in the corneas treated with Chi3l1 small interfering RNA (siRNA), corneas treated with recombinant CHI3L1 before C. albicans inoculation had markedly ameliorated keratitis, reduced fungal load, and decreased polymorphonucleocyte (PMN) infiltration in an interleukin 13 receptor α2 (IL-13Rα2)-dependent manner. CHI3L1 treatment resulted in the induction of the antimicrobial peptides β-defensin 3, CRAMP, and chemokine CXCL10 and its receptor CXCR3 in corneal epithelial cells. Importantly, CHI3L1 administered after C. albicans inoculation also had strong protection against fungal keratitis, suggesting a therapeutic window. This is the first report demonstrating that CHI3L1 is induced during fungal infection, where it acts as an immunomodulator to promote fungal clearance and to regulate antifungal innate immune responses in the cornea.

Distribution and impact of yeast thermal tolerance permissive for mammalian infection

BACKGROUND

From the viewpoint of fungal virulence in mammals, thermal tolerance can be defined as the ability to grow in the 35°C to 40°C range, which is essential for inhabiting these hosts.

RESULTS

We used archival information in a fungal collection to analyze the relationship between thermal tolerance and genetic background for over 4,289 yeast strains belonging to 1,054 species. Fungal genetic relationships were inferred from hierarchical trees based on pairwise alignments using the rRNA internal transcribed spacer and large subunit rDNA (LSU) sequences. In addition, we searched for correlations between thermal tolerance and other archival information including antifungal susceptibility, carbon sources, and fermentative capacity. Thermal tolerance for growth at mammalian temperatures was not monophyletic, with thermally tolerant species being interspersed among families that include closely related species that are not thermal tolerant. Thermal tolerance and resistance to antifungal drugs were not correlated, suggesting that these two properties evolved independently. Nevertheless, the ability to grow at higher temperatures did correlate with origin from lower geographic latitudes, capacity for fermentation and assimilation of certain carbon sources.

CONCLUSIONS

Thermal tolerance was significantly more common among ascomycetous than basidiomycetous yeasts, suggesting an explanation for the preponderance of ascomycetous yeasts among human pathogenic fungi. Analysis of strain maximum tolerable temperature as a function of collection time suggested that basidiomycetous yeasts are rapidly adapting to global warming. The analysis identified genera with a high prevalence of the thermal-tolerant species that could serve as sources of emerging pathogenic fungi.

Twenty years of acanthamoeba diagnostics in Austria

Acanthamoebae are the causative agents of an often seriously progressing keratitis (AK) occurring predominantly in contact lens wearers and can cause several disseminating infections potentially resulting in granulomatous amoebic encephalitis (GAE) in the immunocompromised host. Our institution is the Austrian reference laboratory for Acanthamoeba diagnostics and the aim of this study was to give an overview of proven cases of Acanthamoeba infections in Austria during the past 20 yr. All samples of patients with suspected AK or GAE were screened for Acanthamoeba spp. by culture and/or PCR and the detected amoebae were genotyped. Altogether, 154 cases of AK and three cases of GAE were diagnosed. Age of the AK patients ranged from 8 to 82 yr (mean 37.8) and 58% of the patients were female. Approximately 89% of the AK patients were contact lens wearers, almost all cases were unilateral and 19% of the patients required a keratoplasty. Age of the GAE patients ranged from 2 to 25 yr (mean 14.7), all were HIV-negative, but two were severely immunosuppressed at the time of diagnosis. The predominant genotype in the AK cases was T4, other genotypes found were T3, T5, T6, T10 and T11. The three GAE cases involved genotypes T2, T4 and T5.

An outbreak of invasive fusariosis in a children's cancer hospital

Fusarium is considered an emerging pathogen, and there are few reports of fusariosis in children. The objective of this study was to describe an outbreak of invasive fusariosis in a children's cancer hospital. A neutropenic 17-year-old male patient hospitalized for 10 days for a relapse of acute myeloid leukaemia, under chemotherapy, presented fever without any other symptoms; a thoracic computerized tomography showed bilateral pulmonary nodules. During voriconazole treatment, 1-cm reddened and painful subcutaneous nodules appeared on arms and legs and the culture of a skin biopsy revealed F. solani. Another case occurred 11 days later and started an outbreak investigation. Water samples for cultures were collected from taps, showers and water reservoirs. Air from all patient rooms was sampled. Faucets and the drains of sinks and showers were swabbed and cultured. Environmental and clinical isolates were typed. There were 10 confirmed cases of infection caused by Fusarium spp. F. oxysporum and F. solani were isolated from water, swabs and air in patient rooms. Many control measures were instituted, but the outbreak was only controlled 1 year after the first case, when water filters filtering 0.2 μm were installed at the exit of all faucets and showers in all patient rooms (points-of-use). Typing demonstrated that clinical isolates of F. oxysporum were similar to those of the environment. In conclusion, to our knowledge this is the first reported outbreak of invasive fusariosis in children with oncohaematologic disease. It was controlled using 0.2-μm filters in all tap faucets and showers.

Status of the effectiveness of contact lens solutions against keratitis-causing pathogens

PURPOSE

The aim of this study was to assess the antimicrobial effects of marketed contact lens disinfecting solutions.

METHODS

Using ISO 14729 Stand-Alone Test for disinfecting solutions, bactericidal, fungicidal and amoebicidal assays of eight different contact lens solutions including: ReNu MultiPlus, DuraPlus, Ultimate Plus, OptiFree Express, Kontex Clean, Kontex Normal, Kontex Multisol extra(+), Kontex Soak were performed. The efficacy of contact lens solutions was determined against keratitis-causing microbes, namely: Pseudomonas aeruginosa, Serratia marcescens, Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus, Fusarium solani and Acanthamoeba castellanii.

RESULTS

The results revealed that ReNu MultiPlus, DuraPlus and OptiFree Express were effective in killing bacterial and fungal pathogens as per manufacturer's minimum recommended disinfection time. Ultimate Plus was effective against F. solani and MRSA but ineffective against P. aeruginosa, S. marcescens and S. aureus. Of concern however, is that none of the locally formulated contact lens disinfecting solutions from Pakistan, i.e., Kontex Clean, Kontex Normal, Kontex Multisol extra(+) and Kontex Soak were effective against any of the keratitis-causing organisms tested. All eight contact lens disinfecting solutions were unable to destroy Acanthamoeba cysts.

CONCLUSIONS

Because such ineffective contact lens disinfection solutions present a major risk to public health, these findings are of great concern to the health officials and to the manufacturers of the contact lens disinfection solutions and effective solutions are needed, along with emphasis on proper hygiene for contact lens care and special guidelines for developing countries regarding the manufacture and storage of contact lens disinfecting solutions.

Flagellin-induced expression of CXCL10 mediates direct fungal killing and recruitment of NK cells to the cornea in response to Candida albicans infection

We previously showed that topical flagellin induces profound mucosal innate protection in the cornea against microbial infection, a response involving multiple genes and cell types. In this study, we used a Candida albicans (CA)-C57BL/6 mouse keratitis model to delineate the contribution of CXCL10- and CXCR3-expressing cells in flagellin-induced protection. Flagellin pretreatment markedly enhanced CXCL10 expression at 6 h post CA infection (hpi), but significantly dampened CXCL10 expression at 24 hpi. At the cellular level, CXCL10 was expressed in the epithelia at 6 hpi in flagellin-pretreated corneas, and concentrated at lesion sites 24 hpi. CXCR3-expressing cells were detected in great numbers at 24 hpi, organized within clusters at the lesion sites in CA-infected corneas. CXCL10 or CXCR3 neutralization increased keratitis severity and dampened flagellin-induced protection. CXCR3-positive cells were identified as NK cells, the depletion of which resulted in severe CA keratitis. Contributions from NK T-cells were excluded by finding no change in flagellin-induced protection in Rag1 KO mice. Recombinant CXCL10 inhibited CA growth in vitro and accelerated fungal clearance and inflammation resolution in vivo. Taken together, our data indicate that epithelium-expressed CXCL10 plays a critical role in fungal clearance and that CXCR3-expressing NK cells contribute to CA eradication in mouse corneas.

Survival of Microorganisms on Inanimate Surfaces

In healthcare settings microbial contaminated surfaces play an important role in indirect transmission of infection. Especially surfaces close to the patients’ environment may be touched at high frequencies, allowing transmission from animated sources to others via contaminated inanimate surfaces.

Therefore, the knowledge on the survival of bacteria, fungi, viruses and protozoa on surfaces, and hence, in a broader sense, in the human environment, is important for implementing tactics for prevention of Healthcare-acquired Infections (HAI). This chapter will elaborate the role of surfaces in the transmission of pathogens. Particular emphasis is laid on the current knowledge of the survival time and conditions favouring survival of the pathogens. Finally, mechanisms of transmission from inanimate surfaces to patients are highlighted.

Within the multi-barrier strategy of the prevention of HAI, environmental disinfection policies should be based on risk assessments for surfaces with different risks for cross contamination such as high- and low-touched surfaces with appropriate standards for adequate disinfection measures under consideration of the persistence and infectious dose of the pathogens. As a result, surface disinfection is indicated in the following situations:

Frequently touched surfaces adjacent to patients

Surfaces with assumed or visible contamination

Terminal disinfection in rooms or areas where infected or colonized patients with easily transferable nosocomial pathogens are cared for, and

in outbreak situations.

Furthermore, the knowledge of the persistence of pathogens will also support ensuring the biosafety in microbiological and biomedical laboratories, food-handling settings, and for hygienic behaviour in the everyday life to prevent transmission of infectious diseases.

Role of argon laser as an adjunctive therapy for treatment of resistant infected corneal ulcers

Purpose

To evaluate the role of argon laser as an adjunctive therapy in ten patients with resistant infected corneal ulcers with or without hypopyon.

Methods

The study included 20 patients, split into two groups of ten, with resistant infected corneal ulcers with or without hypopyon. One group was considered as the control group and treated with local and systemic specific antimicrobial drugs guided with culture and sensitivity tests. The other group started with the same specific therapy as the control group for 1 week with no obvious improvement and then was further treated with argon laser. The ten patients in the control group included five cases of fungal ulcers, three mixed (fungal and bacterial) ulcers, and two viral ulcers. The ten patients in the other group included three cases of fungal ulcers, three mixed (fungal and viral) ulcers, three viral ulcers, and one bacterial ulcer as proven with microbial culture and sensitivity tests. Eight cases of the control group and seven cases of the other group were associated with hypopyon. Before laser treatment, a drop of benoxinate hydrochloride 0.4% and a single drop of fluorescein sodium 0.25% were instilled. Argon laser irradiation of the affected cornea was performed using an argon 532 nm wavelength (Carl Zeiss LSL 532s AG; Carl Zeiss Meditec AG, Jena, Germany). A spot size of 500 μm, pulse duration of 0.2 seconds, and power of 900 mW were used. All cases were followed up for 3 months after healing was achieved.

Results

During the first 4 weeks after laser treatment, all patients showed complete healing of the epithelial defect and resolution of stromal infiltration with no adverse effects. In the control group, four cases needed an amniotic membrane graft due to thinning and the other six cases were healed in a duration that ranged from 3 to 7 weeks.

Conclusion

Argon laser phototherapy is useful as an adjunctive treatment for resistant infected corneal ulcers. More cases are needed to get more reliable results and to confirm our findings.

Inefficacy of marketed contact lens disinfection solutions against keratitis-causing Acanthamoeba castellanii belonging to the T4 genotype

The aim of this study was to assess the anti-amoebic effects of marketed contact lens disinfecting solutions. Using amoebistatic, amoebicidal, and cysticidal assays, nine different contact lens solutions were tested including: ReNu MultiPlus, DuraPlus, Ultimate Plus, OptiFree Replenish, OptiFree Express, Kontex Clean, Kontex Normal, Kontex Multisol extra+, Kontex Soak. In vitro growth inhibition (amoebistatic) assays were performed by incubating Acanthamoeba castellanii with aforementioned contact lens disinfection solutions as per manufacturer's instructions in the growth medium for up to 48h at 30°C. To determine amoebicidal and cysticidal effects, amoebae were incubated with contact lens solutions in phosphate buffered saline for 24h and viability was determined by haemocytometer counting as well as re-inoculating them in the growth medium. For controls, solutions were tested against bacterial corneal pathogen, Pseudomonas aeruginosa, as well as amoebae were incubated with the solvent alone. Of the nine contact lens solutions tested, none of them showed potent amoebicidal effects. Only DuraPlus and OptiFree Replenish exhibited trophozoite lysis of 85.3% and 73.7% respectively. In contrast, all contact lens disinfection solutions except Kontex Clean, Kontex Normal, Kontex Multisol extra+, tested showed amoebistatic effects. Importantly, none of the contact lens disinfection solutions exhibited cysticidal effects using qualitative assays, i.e., cysts treated with aforementioned solutions re-emerged as viable amoebae upon inoculation in the growth medium. However, more than 3-log reduction was observed when ReNu MultiPlus, DuraPlus and OptiFree Express were tested against P. aeruginosa which is in accordance with the ISO Stand-Alone Primary acceptance criteria. These findings are of great concern for contact lens users.

Failure of chemotherapy in the first reported cases of Acanthamoeba keratitis in Pakistan

Acanthamoeba keratitis is a painful and progressive infection of the cornea that can result in loss of vision. Here, for the first time in Pakistan, we report two cases of Acanthamoeba keratitis. The first patient was a 37-year-old female who presented with severe itching, redness, pain, along with loss of vision. The patient was a regular soft contact lens wearer. The second patient was a 25-year-old female who had been using soft contact lenses for the past two years. She presented with a burning sensation and extreme pain, along with loss of vision. Both patients were treated for a possible microbial keratitis with topical moxifloxacin hydrochloride drops, vancomycin drops, propamidine isethionate ointment, amphotericin B drops, and amikacin drops. However, the response was inadequate and both patients were referred for corneal transplant. Acanthamoeba castellanii was isolated by placing contact lenses and contact lens cases on non-nutrient agar plates containing a lawn of non-invasive Escherichia coli K-12 HB101 bacteria. The polymerase chain reaction (PCR) using genus-specific probes confirmed the identity of Acanthamoeba spp., whereas the morphological characteristics of trophozoites and cysts were suggestive of A. castellanii in both cases. With growing use of contact lenses for vision correction/cosmetic use coupled with sub-standard lens care in this region and the possibility of non-contact lens-associated Acanthamoeba keratitis, a need for increased awareness of this sight-threatening infection is discussed further.

Outbreak of fungal endophthalmitis due to Fusarium oxysporum following cataract surgery

Outbreak of exogenous Fusarium endophthalmitis after cataract surgery was evaluated. Twenty patients developed postoperative endophthalmitis. In 19 eyes, pars plana vitrectomy (PPV) was performed, in 14 cases (74 %) with primary intraocular lens explantation. In one case, the PPV was not performed because of poor general condition of the patient. Symptoms of endophthalmitis (damaged vision, iritis, tyndallization in anterior chamber, hypopyon) occurred at intervals of 16-79 days (mean 31.3 days). Fungal etiology was documented in 12 eyes (60 %). Fusarium oxysporum was evidenced by culture and/or microscopy and confirmed by PCR and sequencing analysis. Eighteen (90 %) patients were treated with oral voriconazole (400 mg/day) for a period of 4-6 weeks. The final visual acuity was 6/15 in 1 case (5 %), 6/60 and worse in 17 eyes (85 %), and in 2 cases (10 %), enucleation had to be performed. Viscoelastic filling material was suggested the most likely source of infection. Endophthalmitis caused by Fusarium spp. are a potentially big threat for patients with serious impact on vision. Successful management of the infection is highly dependent on early diagnosis including species identification and antifungal susceptibility testing, and on aggressive and long-term treatment.

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.

Antimicrobial activity of alexidine alone and associated with N-acetylcysteine against Enterococcus faecalis biofilm

The purpose of this study was to assess the efficacy of alexidine (ALX), alone and combined with N-acetylcysteine (NAC), in eradicating two Enterococcus faecalis strain biofilms. The biofilms of E. faecalis ATCC 29212 and the clinical isolate E. faecalis D1 were grown in the MBEC-high-throughput device for 24 h and were exposed to five twofold dilutions of ALX (2%–0.007 8%) alone and combined with 100 mg⋅mL⁻¹ NAC, for 1 and 5 min. Eradication was defined as 100% kill of biofilm bacteria. The Student's t-test was used to compare the efficacy of the associations of the two irrigants. After 1-min contact time, ALX eradicated the biofilms at all concentrations except for 0.007 8% and 0.015 6%–0.007 8% with E. faecalis ATCC 29212 and E. faecalis D1, respectively. Similar results for eradication and concentration were obtained when it was combined with 100 mg⋅mL⁻¹ NAC. After 5 min of contact time, ALX alone and combined with NAC eradicated all enterococci biofilms. ALX showed antimicrobial properties against the two E. faecalis strain biofilms tested at very low concentrations, and its combined use with NAC was not seen to enhance its activity.

Loop-mediated isothermal amplification targeting 18S ribosomal DNA for rapid detection of Acanthamoeba

Amoebic keratitis (AK) caused by Acanthamoeba is one of the most serious corneal infections. AK is frequently misdiagnosed initially as viral, bacterial, or fungal keratitis, thus ensuring treatment delays. Accordingly, the early detection of Acanthamoeba would contribute significantly to disease management and selection of an appropriate anti-amoebic therapy. Recently, the loop-mediated isothermal amplification (LAMP) method has been applied to the clinical diagnosis of a range of infectious diseases. Here, we describe a rapid and efficient LAMP-based method targeting Acanthamoeba 18S rDNA gene for the detection of Acanthamoeba using clinical ocular specimens in the diagnosis of AK. Acanthamoeba LAMP assays detected 11 different strains including all AK-associated species. The copy number detection limit for a positive signal was 10 DNA copies of 18S rDNA per reaction. No cross-reactivity with the DNA of fungi or other protozoa was observed. The sensitivity of LAMP assay was higher than those of Nelson primer PCR and JDP primer PCR. In the present study, LAMP assay based on directly heat-treated samples was found to be as efficient at detecting Acanthamoeba as DNA extracted using a commercial kit, whereas PCR was only effective when commercial kit-extracted DNA was used. This study showed that the devised Acanthamoeba LAMP assay could be used to diagnose AK in a simple, sensitive, and specific manner.

TREM-2 promotes host resistance against Pseudomonas aeruginosa infection by suppressing corneal inflammation via a PI3K/Akt signaling pathway

PURPOSE

To explore the role of triggering receptor expressed on myeloid cells 2 (TREM-2) in Pseudomonas aeruginosa (PA) keratitis.

METHODS

BALB/c mice were routinely infected with PA and evaluated at various postinfection time points for corneal expression of TREM-2, by real-time PCR, Western blot, and flow cytometry. Next, BALB/c and C57BL/6 mice were respectively treated with TREM-2 siRNA or agonistic anti-TREM-2 antibody, to determine the role of TREM-2 in PA keratitis. Bacterial load and neutrophil infiltration were tested by plate count and myeloperoxidase assay, respectively. Th1-/Th2-type and proinflammatory cytokine expression were tested by real-time PCR and ELISA after in vivo and in vitro silencing of TREM-2. Moreover, phosphorylated Akt levels were tested by Western blot in murine macrophages after treatment with agonistic anti-TREM-2 antibody. mRNA levels of proinflammatory cytokines were examined in murine macrophages after TREM-2 activation and lipopolysaccharide stimulation, following pretreatment with inhibitors for PI3K or Akt, to determine whether PI3K/Akt is required in TREM-2-mediated immune modulation. In addition, BALB/c mice were treated with wortmannin and analyzed for bacterial load and proinflammatory cytokine expression.

RESULTS

TREM-2 expression was elevated in the infected BALB/c corneas at 3 or 5 days postinfection. Silencing of TREM-2 accelerated disease progression by enhancing bacterial load and corneal inflammation, whereas activation of TREM-2 promoted host resistance to PA keratitis. PI3K/Akt signaling is required in the TREM-2-mediated immune modulation, and inhibition of PI3K resulted in worsened disease after PA corneal infection.

CONCLUSIONS

TREM-2 promoted host resistance to PA infection by suppressing corneal inflammation via activation of the PI3K/Akt pathway.

Protective role of murine β-defensins 3 and 4 and cathelin-related antimicrobial peptide in Fusarium solani keratitis

Antimicrobial peptides (AMPs), such as β-defensins and cathelicidins, are essential components of innate and adaptive immunity owing to their extensive multifunctional activities. However, their role in fungal infection in vivo remains elusive. In this study, we investigated the protective effect of murine β-defensin 3 (mBD3), mBD4, and the cathelicidin cathelin-related antimicrobial peptide (CRAMP) in a murine model of Fusarium solani keratitis. C57BL/6 mice showed significant corneal disease 1 and 3 days after infection, which was accompanied by enhanced expression of β-defensins and CRAMP. Disease severity was significantly improved 7 days after infection, at which time AMP expression was returning to baseline. Mice deficient in mBD3 (genetic knockout), mBD4 (short interfering RNA knockdown), or CRAMP (genetic knockout) exhibited enhanced disease severity and progression, increased neutrophil recruitment, and delayed pathogen elimination compared to controls. Taken together, these data suggest a vital role for AMPs in defense against F. solani keratitis, a potentially blinding corneal disease.

Impact of contact lens materials on multipurpose contact lens solution disinfection activity against Fusarium solani

OBJECTIVE

To investigate the effects of eight different soft contact lenses on disinfection efficacy of a multipurpose solution (MPS) containing polyhexamethylene biguanide (PHMB) against Fusarium solani.

METHODS

Six silicone hydrogel lenses (galyfilcon A, senofilcon A, comfilcon A, enfilcon A, balafilcon A, and lotrifilcon B) and two conventional hydrogel lenses (polymacon and etafilcon A) were placed in polypropylene lens cases filled with MPS containing 0.0001% PHMB and soaked for 6, 12, 24, 72, and 168 hours. After each interval, depleted MPS from lens cases were removed and assayed for activity against F. solani according to International Organization for Standardization (ISO) 14729 stand-alone procedure. A portion was aliquoted for chemical analysis.

RESULTS

Soaking etafilcon A, balafilcon A, and polymacon lenses for 6 hours reduced the concentration of PHMB in MPS by more than half the stated labeled concentration, with concentrations below the limit of detection for etafilcon A-depleted and balafilcon A-depleted solutions after 12 and 72 hours of soaking, respectively. Except for comfilcon A-depleted solutions, all others failed to consistently obtain one log reduction of F. solani. The solutions soaked with etafilcon A, balafilcon A, and polymacon lenses for 24 hours or more lost all or almost all fungicidal activity against F. solani.

CONCLUSIONS

Over time, the disinfectant uptake by some lenses can significantly reduce the PHMB concentration and the fungicidal activity of the MPS against F. solani. Current ISO methodology does not address the reduction in microbiocidal efficacy when lenses are soaked in MPS. The ISO committee should consider adding "soaking experiments" to quantify the effect that contact lens materials have on the performance of MPSs.

Rapid and sensitive diagnosis of Acanthamoeba keratitis by loop-mediated isothermal amplification

A loop-mediated isothermal amplification (LAMP) assay was developed for the detection of Acanthamoeba. The sensitivity of the LAMP assay was tested using different copies of positive DNA. The specificity of the assay was tested using DNA extracted from Acanthamoeba, Pseudomonas aeruginosa, Candida albicans, herpes simplex virus-1 and human corneal epithelial cells. Its effectiveness was evaluated and compared with culture, corneal smear examination and real-time PCR in corneal samples from mice with Acanthamoeba keratitis. We also tested three corneal samples from patients with suspected Acanthamoeba or fungal infection using LAMP. Loop-mediated isothermal amplification was confirmed to be very sensitive, with the lowest detection limit being ten copies/tube of Acanthamoeba DNA. The LAMP primers only amplified Acanthamoeba DNA. During the development of Acanthamoeba keratitis in mice, almost all of the positive rates of LAMP at each time post-infection were higher than those of culture or corneal smear examination. The total positive rate of LAMP was significantly higher than those of culture and corneal smear examination (p <0.05), whereas the sensitivities of LAMP and real-time PCR were comparable. However, the trends of positive change in these different test methods were generally similar. Of the three clinical corneal specimens, two with suspected Acanthamoeba keratitis tested positive for Acanthamoeba using LAMP along with culture or corneal smear examination, whereas the other suspected fungal keratitis tested negative. The LAMP assay is a simple, rapid, highly specific and sensitive method for the diagnosis of keratitis caused by Acanthamoeba.