The influence of donor factors on corneal organ culture contamination

Investigating the Influence of Temperature and Supplementation Timing on Antifungal Efficacy in Storage Medium for Corneal Transplantation

INTRODUCTION

Although antifungal supplementation reduces the fungal load in the corneal storage medium, consensus is lacking on the influence of dosing and temperature. The study aims to evaluate the impact of eye bank warming protocol and timing of antifungal supplements on efficacy in Optisol-GS and tissue.

METHODS

Corneoscleral rims contaminated with Candida albicans (C. albicans) were incubated in Optisol-GS, either without antifungal agents or with the addition of amphotericin B or voriconazole at various concentrations (2 ×, 5 ×, 10 ×, and 20 × MIC), at different time points, and under various preservation temperatures (2-8 °C versus 2 h-room temperature exposure). Antifungal efficacy was evaluated by counting viable yeast colonies cultured from Optisol-GS samples. Tissue sterility was determined through direct tissue culture and histological examination of the contaminated rims after a 14-day incubation period.

RESULTS

Room temperature exposure did not increase colony growth at the same multiple MIC of antifungal agents. Although antifungal addition reduced C. albicans growth in a concentration-dependent manner, yeast growth was still observed in all Optisol-GS samples with a single supplementation after a 14-day incubation. Only groups with additional antifungal supplementation on either day 2 or day 6 showed a 99% or greater reduction of C. albicans growth in Optisol-GS samples and yielded negative results in direct tissue culture.

CONCLUSIONS

The eye bank warming protocol did not compromise antifungal efficacy. To sustain the required concentration and effectively reduce C. albicans growth in Optisol-GS and contaminated tissue, additional antifungal supplementation on either day 2 or day 6 was necessary during a 2-week preservation period.

Whole mount immunofluorescence analysis of fresh and stored human donor corneas highlights changes in limbal characteristics during storage

PURPOSE

Human donor corneas are an essential control tissue for corneal research. We utilized whole mount immunofluorescence (WM-IF) to evaluate how the storage affects the tissue integrity and putative limbal stem cells in human and porcine corneas. Moreover, we compare this information with the marker expression patterns observed in human pluripotent stem cell (hPSC)-derived LSCs.

METHODS

The expression of putative LSC markers was analyzed with WM-IF and the fluorescence intensity was quantified in human donor corneas stored for 1-30 days, and in porcine corneas processed 0-6 h after euthanasia. The results were compared with the staining of human and porcine corneal cryosections and with both primary and hPSC-derived LSC cultures.

RESULTS

WM-IF analyses emerged as a more effective method when compared to tissue sections for visualizing the expression of LSC markers within human and porcine corneas. Storage duration was a significant factor influencing the expression of LSC markers, as human tissues stored longer exhibited notable epithelial degeneration and lack of LSC markers. Porcine corneas replicated the expression patterns observed in fresh human tissue. We validated the diverse expression patterns of PAX6 in the limbal-corneal region, which aligned with findings from hPSC-LSC differentiation experiments.

CONCLUSIONS

WM-IF coupled with quantification of fluorescence intensities proved to be a valuable tool for investigating LSC marker expression in both human and porcine tissues ex vivo. Prolonged storage significantly influences the expression of LSC markers, underscoring the importance of fresh human or substitute control tissue when studying limbal stem cell biology.

Microbiological screening of corneas stored in organ culture medium at Lions Eye Bank of Western Australia from 2011 to 2022

PURPOSE

The purpose of this study was to analyse the contamination rate of corneal samples stored in OCM at Lions Eye Bank of Western Australia over a 12-year period.

METHODS

All OCM samples used to preserve corneas from 2011 to 2022 (inclusive) underwent microbiological testing. Samples were collected into aerobic and anaerobic culture bottles on day 3-5 of corneal preservation and 24 h after transfer to thinning medium. Samples were tested for 7 days using the BACTEC FX system. Corneas remained in quarantine until clearance was obtained.

RESULTS

From 2011 to 2022, 3009 corneas were retrieved and 2756 corneas were stored in OCM. Thirty one (1.1%) positive samples were reported, with 20 growths of bacterial origin and 11 fungal. Microbial contamination was mostly identified on day 1 of culture (77.5%). Donors of contaminated samples had a mean age of 55 years, with 17 male and 14 female donors. The highest incidence of contamination came from donors whose cause of death was cancer. Death to enucleation times of contaminated samples ranged from 3.5 to 25.5 h (mean = 13.5 ± 7.3) and death to preservation time ranged from 4.1 to 27.5 h (mean = 14.8 ± 7.2). These did not significantly differ from the average time from death to enucleation (mean = 13.9 ± 3) and death to preservation (mean = 16.3 ± 4.2) of non-contaminated samples.

CONCLUSION

Microbiological screening of corneas stored in OCM at LEBWA showed a very low rate of positive cultures with no predictive donor characteristics.

Donor related corneal graft infection: a review of literature and preventive strategies

PURPOSE

Donor-related infections are a serious threat to patient safety after corneal transplantation. We provide a concise review of literature from the last decade on donor-related graft infections, sources of contamination and means to reduce the contamination of donor tissue and preservation media.

METHODS

We reviewed 50 papers from year 2005 to 2021 related to donor-related graft infections. We included 14 studies related to the risk factors associated with post-keratoplasty infection and preventive methods.

RESULTS

Incidence of post-keratoplasty infections has been reported to be approximately 0.2%-0.77% for endophthalmitis and 6.5%-10.5% for microbial keratitis. We analyzed six important studies regarding the risk factors related to donor contamination. It was observed that younger donor age, increased death to retrieval time, warming cycles and increased eye bank processing time and positive corneo-scleral rim cultures were important risk factors for donor-related infections post keratoplasty. Eye banks have adapted newer protocols over the time period for prevention of donor-related contamination. Recommended preventive strategies were published in about eight important studies over the past decade. In addition to meticulous donor screening, rapid warming cycles, double contact with povidone iodine during retrieval and addition of antifungals like amphotericin B, Voriconazole and cycloheximide have been suggested over the last decade although their use is still in debate with regard to the efficacy, toxicity and cost-effectiveness.

CONCLUSION

The last decade has witnessed a relative rise of fungal infections and multidrug resistant bacterial infections post-keratoplasty. Eye bank prepared corneas for lamellar surgeries are at increased risk for donor contamination due to increased exposure to the higher temperatures during their processing. Addition of antifungals and broad spectrum antibiotics to the hypothermic preservation media needs to be considered in the new era of increasing trends of lamellar keratoplasty.

Comparison of Microbial Sampling Sites and Donor-Related Factors on Corneal Graft Contamination

Grafts used for corneal donation should be sterile to avoid transplantation failure and secondary infection. However, there are no clear and globally accepted specifications from eye banks on microbial sampling sites. The objective of this study was to analyze microbial contamination of corneal grafts collected from different sampling sites. We found that the contamination rates and strain compositions significantly differed at different sampling sites. To clarify the effect of the microbial sampling site on corneal graft contamination, microbial sampling was conducted using 30 corneal grafts at the extraocular and intraocular sides of the graft in 2020 from the National Eye Bank of Taiwan. Microbial contamination significantly differed (p < 0.05) between the different sampling sites on the graft according to McNemar’s test. Although the two sampling sites showed the same specificity (33.33%), the sensitivity of sampling on the extraocular side (82.35%) was higher than that on the intraocular side (17.65%) of the graft. Donor-associated factors, including the cause of death, operating place, and cold compression, were analyzed using chi-square statistics, which revealed no significant differences in microbial contamination. Thus, our data provide evidence for the microbial sampling site of donated grafts and clear specifications for maintaining the quality of corneal grafts.

Clinical outcomes of long-term corneas preserved frozen in Eusol-C used in emergency tectonic grafts

To report the clinical results on the use of corneas frozen in Eusol-C as tectonic corneal grafts.Retrospective review of medical records of patients who received frozen corneas as emergency tectonic grafts from 2013 to 2020. Corneas had been stored in Eusol-C preservation media at − 78 °C for a mean time of 6.9 months. Diagnosis, transplant characteristics, microbial culture results, anatomic integrity, epithelial healing, neovascularization, transparency, infection and need for additional surgeries were registered. Fifty corneas were used in 40 patients (mean age 60.5 years, 20 males) with a median follow-up of 27.3 months after surgery. Need for tectonic graft was due to: perforation secondary to immune diseases (6, 12%), neurotrophic ulcer (11, 22%), trauma (3, 6%), corneal infection (11, 22%), chronic disorders of the ocular surface (9, 18%) and previous corneal graft failure (10, 22%). Mean size of grafts was 5.6 mm and 36 cases (72%) also received an amniotic membrane graft. Thirty-eight corneas achieved epithelization (76%), 25 (50%) were clear and 19 (38%) developed neovascularization. None of the corneas were rejected. Seventeen corneas (34%) failed: 7 (14%) due to reactivation of baseline disease and 10 (20%) due to primary graft failure. Four corneas (8%) had positive microbial cultures suggestive of contamination and 2 (4%) developed a cornea abscess non-related to a positive microbial culture. Long-term preservation of donor corneas in Eusol-C at − 78 °C is a viable technique to meet the needs of emergency grafts with minimal equipment.

Analysis in Results of Microbiologic Exam Related to Donor Corneas

Purpose: This study analyzed the microorganisms identified in donor corneas and their clinical significance.Methods: The medical records of 94 patients (114 eyes) who underwent keratoplasty and microbiological tests of the donor corneas from October 2008 to December 2020 at our hospital were reviewed retrospectively. During keratoplasty, we conducted microbiological tests of the corneoscleral rim of the donor cornea and preserving solution Optisol™-GS (Bausch & Lomb, Rochester, NY, USA), and examined the antibiotic susceptibility of bacterial isolates from the cultures.Results: Some isolates of domestic donor corneas revealed bacteria, but none of the imported corneas did. Gram-negative bacilli were detected from the corneoscleral rim in three eyes (2.6%): two cases of Acinetobacter baumannii/haemolyticus and one case of Pseudomonas aeruginosa. In one case (0.9%), Acinetobacter baumannii/haemolyticus was identified from preserving solution, with no bacteria found in the corneoscleral rim. Antibiotic susceptibility tests showed multi-drug resistance, except to colistin. In all cases where bacteria were detected, there was no keratitis or endophthalmitis after corneal transplantation.Conclusions: Although rare, bacteria can be identified from donor corneas or the preserving solution used in corneal transplantation. Therefore, caution is needed in all processes dealing with donor corneas. Empirical antibiotics that have sufficient antimicrobial activity to suppress multi-drug resistant bacteria should be selected in corneal transplantation.

Eye bank and theatre factors for positive microbiological culture of corneoscleral rim and cornea storage medium in the real-world

OBJECTIVES

To evaluate microbiological culture rate and positivity of corneoscleral rim and cornea storage media as well as possible risk factors for contamination with real-world data.

METHODS

Data of consecutive cornea donors implanted in the reference centre from January 2013 to January 2018 were reviewed. Information about cornea characteristics (donor demographic data, endothelial cell density, type of cornea conservation, days of storage, and precut vs full-thickness tissue), and microbiological culture information (corneoscleral rim vs storage sample, positive result) were statistically analysed.

RESULTS

During the study period, 1369 corneas (737 donors) were implanted. Cultures were performed in 76.8% (n = 1052) of them and were positive in 3.2% of cases, mainly bacteria (84.4%). Corneas preserved in hypothermia represented 61.8% of all positive microbiology results (p < 0.001). Other analysed risk factors did not reach statistically significant association with microbiological positivity. None of the 34 cases with positive microbiological cultures reported ocular infection for the recipients in at least 6 months' follow-up.

CONCLUSIONS

Microbiological tests rate in real-world practice are high despite not being compulsory. Organotypic cultured corneas showed a statistically less positivity in corneoscleral and storage medium than hypothermic ones, resulting in another advantage of this kind of cornea storage. Although precut corneas are thought to present less microbiological positivity, a statistically significant association was not found in the present study.

Translational and Regulatory Challenges of Corneal Endothelial Cell Therapy: A Global Perspective

Cell therapies are emerging as a unique class of clinical therapeutics in medicine. In 2015, Holoclar (ex vivo expanded autologous human corneal epithelial cells containing stem cells) gained the regulatory approval for treating limbal stem cell deficiency after chemical eye burn. This has set a precedent in ophthalmology and in medicine, reinforcing the therapeutic promise of cell therapy. However, to generalize and commercialize cell therapies on a global scale, stringent translational and regulatory requirements need to be fulfilled at both local and international levels. Over the past decade, the Singapore group has taken significant steps in developing human corneal endothelial cell (HCEnC) therapy for treating corneal endothelial diseases, which are currently the leading indication for corneal transplantation in many countries. Successful development of HCEnC therapy may serve as a novel solution to the current global shortage of donor corneas. Based on the experience in Singapore, this review aims to provide a global perspective on the translational and regulatory challenges for bench-to-bedside translation of cell therapy. Specifically, we discussed about the characterization of the critical quality attributes (CQA), the challenges that can affect the CQA, and the variations in the regulatory framework embedded within different regions, including Singapore, Europe, and the United States. Impact statement Functional corneal endothelium is critical to normal vision. Corneal endothelial disease-secondary to trauma, surgery, or pathology-represents an important cause of visual impairment and blindness in both developed and developing countries. Currently, corneal transplantation serves as the current gold standard for treating visually significant corneal endothelial diseases, although limited by the shortage of donor corneas. Over the past decade, human corneal endothelial cell therapy has emerged as a promising treatment option for treating corneal endothelial diseases. To allow widespread application of this therapy, significant regulatory challenges will need to be systematically overcome.

Use of Corneas From Septic Donors for Descemet Membrane Endothelial Keratoplasty

PURPOSE

To evaluate the suitability of corneas from septic donors for transplantation by analyzing the discard rate in the eye bank and the clinical outcome of Descemet membrane endothelial keratoplasty (DMEK) using organ-cultured corneal grafts from septic versus nonseptic donors.

METHODS

This retrospective study included 1554 corneas of which 456 corneas (29%) were from septic and 1072 corneas (69%) from nonseptic donors [for 26 corneas (2%) sepsis status was unknown]. The clinical outcome at 6 months after DMEK was evaluated for 82 grafts (26 from septic and 56 from nonseptic donors). Outcome measures were endothelial cell density, central corneal thickness, and postoperative complications.

RESULTS

Primary discard rates were higher for corneas from septic than from nonseptic donors (32.9% vs. 24.5%, P = 0.001). The main discard reason was poor endothelial cell quality for both septic (13.8%) and nonseptic (11.8%) donor corneas. Eye bank contamination rates for septic and nonseptic donor corneas were 1.1% and 1.7%, respectively (P = 0.102). After DMEK, donor endothelial cell density at 6m postoperatively was comparable between grafts from septic and nonseptic donors (1410 ± 422 cells/mm vs. 1590 ± 519 cells/mm, P = 0.140). No differences in 6m central corneal thickness and in the rebubbling rate were observed between the 2 groups (P = 0.780 and P = 0.396, respectively). None of the cases had graft rejection nor endophthalmitis in both groups.

CONCLUSIONS

Provided strict adherence to donor screening and evaluation protocols, the use of organ-cultured corneas from septic donors for DMEK does not seem to increase the risk for recipients and allows for expansion of the donor pool for corneal tissue.

Changes of Contamination Rate and Microorganism Evaluation in Organ-Cultured Human Corneas: A 14-Year Review From a French Regional Eye Bank

PURPOSE

This study aimed to assess how the contamination rate of organ-cultured corneas has evolved and to analyze the evolution of microorganisms involved.

METHODS

Data from the Besançon eye bank were reviewed over 14 years (2005-2018). The changes in the contamination rate and the contaminant species found during the organ culture storage were analyzed. Microbiological tests were performed twice on the storage media-at day 5 and before the deswelling phase.

RESULTS

Among the 17,979 donor corneas collected, 1240 corneas were microbiological-test positive. The average annual contamination rate was 6.8% (range: 5.2%-8.9%). Seventy-five percent of contaminations were bacterial. The most frequently found bacterium was Staphylococcus spp. (31.3%), followed by non-Enterobacteriaceae Gram-negative Bacilli (GNB) (27.3%), with most Sphingomonas spp. and Pseudomonas spp. Fungal contamination (21.9%) was dominated by Candida (82.7%). Seventy-seven types of microorganisms were identified. The Staphylococcus rate tended to decrease, whereas non-Enterobacteriaceae GNB rate has increased in the past few years to reach 46% of bacteria. Most of the contaminations were detected in the early phase of organ culture at day 5 (89.2%). The second microbiological test found 44.8% of fungal contaminations (predominantly Candida spp.).

CONCLUSIONS

The annual contamination rate was stable and remains low, but the types of contaminating microorganisms varied from year to year. Staphylococcus spp. and non-Enterobacteriaceae GNB accounted for a significant proportion of the contaminations. We found a significant proportion of contamination, especially fungal, at the late phase of storage. Reassessing the antibiotics and antifungals in the storage medium may be useful to limit corneal disposal.

Factors influencing endothelial cell density of corneas for transplantation

To evaluate factors affecting corneal endothelial cell density (ECD) under enucleation and preservation time studies at Eye Bank of the Federal District of Brazil. We conducted a case-control study collecting data from 1128 corneas where death-to-enucleation time and enucleation-to-preservation time were within 24 h. Low cell count were those corneas with an ECD less than 2000 cells/mm² and high cell count was defined as those with ECD greater than 2000 cells/mm². We calculated the independent risk factors related to: cause of death, donor age, death-to-enucleation time, enucleation-to-preservation time and primary graft failure. Correlation analysis was used to assess which parameters influence ECD: death-to-enucleation time, enucleation-to-preservation time, average cell area (AVE), coefficient of variation and percentage of hexagonal cells. Of the total number of corneas, 1004 had ECD data and were selected for the study. 87.4% (n = 877) had high cell counts with 2699 ± 412 cells/mm². The mean donor age was 38.8 ± 16 years. The most common causes of death were external causes (48.6%, n = 488). Longer times from death-to-enucleation, up to 24 h were not associated with a decrease in ECD (OR 0.58; P = 0.44) or risk of graft survival (P = 0.74). Enucleation-to-preservation intervals greater than 12 h showed increased risk of graft survival (P = 0.04). AVE was the main parameter for ECD (R² = 0.96, P < 0.001). The overall graft survival rate was 98.2% (n = 761). Donors with 40 years of age and above did not present a higher risk of graft survival (P = 0.09). We suggest that the maximum time from death-to-enucleation should be 24 h, assuming the body has been refrigerated after 6 h; and from enucleation-to-preservation time of 12 h, followed by proper processing and cornea morphology examination.

Cornea Procurement and Processing up to 72 Hours: No Risk for Cornea Transplant Quality

Background

The realization of tissue donations is bound to a tight timeframe. Depending on the type of tissue, time limits are specified within which the donation must be procured and processed. Otherwise, there is a risk of tissue quality loss with increasing time intervals from cardiovascular arrest. According to the European Directorate for the Quality of Medicines and HealthCare (EDQM) guide, cornea must be procured and processed within 72 h after death. The question arises whether this time interval has an influence on the quality of transplanted tissues and how it affects the accomplishment of tissue donations.

Methods

In order to obtain information on this, the numbers of tissue donations in the network of the German Society for Tissue Transplantation (DGFG) were evaluated as a function of the death to retrieval time (DRT) as well as the death to preservation time (DPT). For this purpose, 21,454 database entries of cornea donations made in the period from 2014 to 2018 were included.

Results

The results show that nearly 50% of donations realized in the DGFG network could be processed only 48 h or later after cardiovascular death due to the opt-in regulation in Germany. For these donations, there seems to be a higher discard rate compared to donations taken earlier. Nevertheless, there is a transplantation rate for these grafts of more than 65%, which is comparable to average transplantation rates stated in the literature.

Conclusion

All corneas finally selected for transplantation must meet the specified quality parameters. Since this naturally also applies to transplants that could only be procured at later time points, it can be concluded that DPT up to 72 h for corneal tissue is adequate and has no influence on the quality of corneas that are ultimately transplanted.

Microorganism detection and contamination rate of donor eyes in Japan

PURPOSE

To evaluate the microorganism detection and contamination rate of donor eyes.

STUDY DESIGN

Retrospective study.

METHODS

In this retrospective study, we reviewed all donor cornea data collected from Kyoto Prefectural University of Medicine (KPUM) Eye Bank, Kyoto, Japan from April 2015 to June 2018, including microbiologic data obtained from conjunctival swabs and preservation medium and findings of postoperative infection from the medical records.

RESULTS

During the study period, 77 eyes from 44 deceased individuals (mean age at time of death: 75 ± 17.3 years [range, 30-102 years]) were donated to the KPUM Eye Bank after being harvested using standard safety precautions and disinfection procedures. In 49 of the 77 eyes (63.6%), the conjunctival-swab culture revealed microorganisms, with the 3 most commonly detected being methicillin-resistant Staphylococcus epidermidis (MRSE), methicillin-sensitive S aureus (MSSA), and methicillin-resistant S aureus (MRSA). The data revealed positive microorganism detection in only 4 (5.2%) of the 77 donor-cornea storage-medium cultures. Positive microorganism detection was found in all the age groups, with no statistical difference between the groups (P > .05). In the eyes enucleated ≥ 2.5 h postmortem, a higher positive microorganism detection occurred (P = .03). During the postoperative follow-up period, there was no record of corneal infection.

CONCLUSIONS

The preenucleation conjunctival-swab-culture findings revealed that the rate of positive microorganism detection was similar for advanced-age and younger-age donors and that a shorter elapsed time from donor death to postmortem enucleation resulted in less donor-microorganism contamination.

Corneae from body donors in anatomy department: valuable use for clinical transplantation and experimental research

Background

Explanted corneae are highly needed for the surgical management of patients with severe corneal diseases. The aim of this study was to determine whether the body donors from the Institute of Anatomy are a suitable source of donor corneae.

Methods

At the Institute of Anatomy at Saarland University Medical Center in Homburg, corneae are prelevated from body donors who had consented to the removal of tissues for transplantation purposes during their lifetime. Following the report of death, the LIONS Eye Bank is informed and the contraindications of corneal explantation are clarified. Obtaining a blood sample within 24 h postmortem is mandatory.

Results

The Institute of Anatomy had 150 body donors in the time period from January 2018 to June 2019. Out of these, 68 (45.3%) were reported to the Eye Bank. The age of the donors (median 82 years (range: 57–96)) is not critical since the quality of the corneae depends on the number of endothelial cells (mean: 2109 ± 67 cells/mm² (range: 511–2944 cells/mm²)). Contraindications were present in 19 (12.6%) cases. The corneae were extracted from 49 (32.7%) body donors. Out of these 98 corneae, 46 (46.9%) were successfully transplanted. Of all non-transplanted corneae, 6 (6.1%) were microbiologically contaminated, 10 (10.2%) had a positive serology, 22 (22.5%) had an endothelial cell count < 2000 cells/mm² and 6 (6.1%) are at time of this analysis still in culture medium. The non-transplanted tissues were used for research.

Conclusions

Explanted corneae from the Institute of Anatomy are a valuable option in obtaining grafts for corneal transplantation, which is why we are working toward on expanding cooperation with this department.

Intensive care unit time and prolonged enucleation to processing interval are associated with donor cornea contamination

PURPOSE

To determine donor cornea contamination rate and to determine factors associated with cornea contamination. To assess the effect of hospitalization, intensive care unit (ICU) time, and antibiotic use on corneal contamination rate. To determine the spectrum of the contaminating microorganisms.

METHODS

The contamination rate of 212 corneas, obtained by enucleation from April 2014 to January 2015 in a single eye bank, was assessed retrospectively according to age, sex, cause of death, systemic antibiotic use, hospitalization time, ICU time, mechanical ventilation (MV), death to enucleation interval (DEI), enucleation to processing interval (EPI), and corneal epithelial exposure grading. The relative risk (RR) and adjusted RR with a 95% confidence interval were calculated using IBM-SPSS 20.0.

RESULTS

The contamination rate was 35.6% (n = 75). On multivariate analysis, ICU stay of 4 days or longer and enucleation to processing interval (EPI) greater than 7.4 h (RR 1.58, CI 0.96-2.60, P = 0.06) were associated with donor cornea contamination. Corneal contamination risk was highest from 4 to 6 days at the ICU (RR 3.40, CI 1.54-7.51, P < 0.01) and decreased after 7 days (RR 2.22, CI 1.00-4.93, P = 0.05). Coagulase-negative Staphylococcus was the most common isolated bacteria (69.6%). The frequency of gentamicin-resistant bacteria was higher among patients who stayed 4 days or longer at the ICU.

CONCLUSION

Patients staying at the intensive care unit 4 days or longer showed increased risk of corneal contamination. This is an important result to consider further indication for cornea donation.

In vitro susceptibility of microorganisms isolated from cold stored corneas: increased gentamicin-resistance in cornea banking

Donor cornea contamination is one of the major risks for corneal transplants. The use of antibiotics in storage media remains as one of the most important security measurements to minimize the contamination risk in corneal preservation. Since antibiotic resistance among microorganisms have been rising gradually, it is important to gain knowledge about the antimicrobial susceptibility pattern for choosing the most suitable antimicrobial agents. Thus, we evaluated the in vitro susceptibility of microorganisms isolated in donor corneas processed at the Center for Blood Transfusion, Tissues and Cells (Córdoba, Spain) during 4 years in order to evaluate the efficiency, and to promote changes for further antibiotics use. Our results show the high rate of resistance to gentamicin, an antibiotic used in corneal preservation media such as Optisol GS and Eusol-C. Conversely, all the analyzed microorganisms were sensitive to vancomycin. This suggests the possibility of replacing gentamicin with another more effective antibacterial agent such as vancomycin.

Fungal infection after keratoplasty and the role of antifungal supplementation to storage solution: a review

Fungal infection after corneal transplantation is a rare, yet potentially devastating, postoperative complication and has become a growing concern for the transplant surgeon and eye banking community. The Eye Bank Association of America (EBAA) has reported an increasing trend in the rate of postkeratoplasty fungal infections and a reversal in the previously documented predominance of bacterial over fungal infections. Additionally, several studies have confirmed a high correlation between positive corneoscleral donor rim fungal cultures and postoperative infections. Optisol GS (Bausch & Lomb, Irvine, California, USA), the most extensively used corneal storage solution in US eye banks, does not currently contain any antifungal supplementation. Although large randomised control trials evaluating the efficacy and safety of routine antifungal supplementation to corneal storage solution are lacking, several investigative studies have assessed the role of antifungal agents in reducing fungal contamination of donor corneas without causing undue corneal toxicity. This review will present the current epidemiology of postkeratoplasty fungal infections and evidence for obtaining routine fungal rim cultures and antifungal supplementation of storage solution.

Prevalence of microbial contamination in donor corneas

BACKGROUND/PURPOSE:

Postoperative infection is the most disastrous complication of penetrating keratoplasty (PK). Corneoscleral rim culture provided information regarding subsequent infections. Our aims were to identify the incidence of microbial contamination in donor corneas and to report the recovery of bacteria with two culture methods, i.e., conventional culture media after aerobic/anaerobic cotton swabs and blood culture media (Fastidious Antibiotic Neutralization [FAN]).

MATERIALS AND METHODS:

A total of 118 patients underwent PK. Corneoscleral rim cultures were performed using aerobic/anaerobic culture cotton swabs (Transystem™, COPAN, Italia) with subsequent convention media and blood culture media (FAN bottle, BD BACTEC™, USA). The results of the different methods were reported and analyzed.

RESULTS:

Microorganisms were recovered from 24 in total 118 cases (20.3%, n = 118), 14 from blood culture media (FAN) (11.8%, n = 118), 9 from conventional culture media after aerobic/anaerobic cotton swabs (7.63%, n = 118), and 2 from fungus culture (1.69%, n = 118). The most commonly identified pathogen was coagulase-negative Staphylococcus (CoNS) (n = 13, 54.2%), and more isolates of CoNS and staphylococcus aureus were recovered from blood culture media (FAN) than those from conventional culture media after aerobic/anaerobic cotton swabs (13 vs. 4, P = 0.05). Conversely, more nonfermentative Gram-negative bacilli were recovered from conventional culture media after aerobic/anaerobic cotton swabs. None of the 24 cases with positive corneoscleral rim cultures reported ocular infection for the recipients in at least 6 months’ follow-up.

CONCLUSION:

The conventional culture media after aerobic/anaerobic cotton swabs and blood culture media (FAN) did not yield identical isolates of bacteria. The blood culture media (FAN) could further yield Gram-positive bacteria in addition to those recovered from convention media. It seemed adding gentamicin and streptomycin could achieve bacteriostatic effect instead of the bactericidal effect. The administration of postoperative antibiotic in the recipient was suggested.

Microbiological contamination in donor corneas preserved for medium-term

To evaluate the characteristics of microbiological contamination in donor corneas preserved for medium-term. A total of 82 donated corneas from June 1, 2014 to November 30, 2014 were retrospectively analyzed. The corneas were preserved in cornea chambers medium-term solution at 4-8 °C for keratoplasty. After removal of the central corneas for transplantation, the corneoscleral rims were put back into the medium for 1 month at room temperature (20-25 °C). The suspicious contaminated storage solutions indicated with transparency or color change were examined with bacteria and fungi cultivation for strain identification. The data collected included gender, age, procurement site and causes of death of donors, and follow-up of recipients. Statistical analysis was performed using Microsoft Excel and SPSS 24.0. Significance level was set at a P value < 0.05. The overall pathogen positive rate was 9.8% (n = 8), including 7 (87.5%) fungi and 1 (12.5%) bacteria. They were 2 (2.44%) Fusarium, 2 (2.44%) Chromomycosis, 1 (1.22%) Candida albicans, 1 (1.22%) Aspergillus versicolor, 1 (1.22%) Acremonium species, and 1 (1.22%) Enterococcus. 5 contaminated corneas were used for penetrating keratoplasty; although four out of five (80%) had not been given antifungal drugs during more than 6 months following-up period, none of the recipients was infected with a graft. Donor age (P = 0.839), gender (P = 0.062), procurement sites (P = 0.713) and cause of death (P = 0.711) had no statistically significant influence on the contamination rate. All donor corneas have a possibility of microbiological contamination. Strict tissue preservation protocol but not antifungal drugs following keratoplasty seems necessary to prevent graft infection.

Factors Affecting Corneal Organ Culture Contamination: A 6-year Study at the New South Wales Tissue Bank

PURPOSE

To report the rate of microbial contamination and analyze possible risk factors for contamination of banked corneas stored using the organ culture method.

METHODS

Data from the New South Wales Tissue Banks incorporating the Lions NSW Eye Bank, between September 1, 2011, and November 30, 2017, were reviewed retrospectively. All corneas collected during this period and stored in organ culture storage media were tested for microbial contamination. The influence of potential factors on the rate of contamination was analyzed using the χ test and logistic regression using generalized estimating equations.

RESULTS

A total of 4410 corneas were included in this study, of which 110 were medium culture positive, representing a microbial contamination rate of 2.5%. The main contaminants were Candida species followed by Staphylococcus species. Corneal tissue collected in summer and autumn had a significantly higher contamination rate (P = 0.006). All other factors studied were not shown to have a statistically significant association with contamination after accounting for within-pair correlation and confounders.

CONCLUSIONS

A relatively low contamination rate of 2.5% observed in our study reflects the stringent laboratory protocols, strict donor selection criteria, and high level of experience among staff at the Lions NSW Eye Bank. Our study demonstrated that the season of collection had a strong association with the rate of organ culture contamination. Because Candida species contributed the largest percentage of contamination, specific measures to reduce and eliminate fungal proliferation should be considered by eye banks particularly in warm seasons.

Donor characteristics and risk factors for methicillin-resistant Staphylococcus aureus contamination in storage medium for corneal transplantation: A 10-year retrospective study

PURPOSE

This study investigated the donor characteristics of methicillin-resistant Staphylococcus aureus (MRSA) contamination in storage medium before transfer of corneas to preservation medium for corneal transplantation, in order to identify donor characteristic risk factors for MRSA contamination.

METHODS

This retrospective, cross-sectional study was performed using Juntendo Eye Bank records for all corneal transplantation procedures. Storage medium (EP-II^® ) cultures for right eyes were included for the period between July 2008 and December 2017. The following donor characteristics were collected: age, sex, cause of death, history of cataract surgery, death-to-enucleation interval, death-to-preservation interval, and endothelial cell density (ECD). Donor characteristics were compared between MRSA and non-MRSA contamination groups. Odds ratios (ORs) for donor-related risk factors for MRSA contamination were determined using logistic regression.

RESULTS

In total, 370 storage medium samples were examined; 222 were positive for bacterial cultures (60.0%) and 36 were MRSA-positive (9.7%). Donor age was significantly higher in the MRSA contamination group than in the non-MRSA contamination group (86.1 ± 9.5 years vs 75.9 ± 15.9 years, P < 0.001). Univariate logistic regression analysis showed that MRSA contamination risk factors were older age (OR = 1.07; 95% confidence interval [95% CI]: 1.03-1.11) and decreased ECD (OR = 0.9993; 95% CI: 0.9986-0.9992). The fully adjusted OR for every year of age as a risk factor for MRSA contamination was 1.07 (95% CI: 1.03-1.11).

CONCLUSIONS

Aging was a risk factor for MRSA contamination in storage medium. Careful pre-banking assessment of elderly donor corneas is needed to prevent intractable postoperative MRSA infection.

Microbiological Screening of Hypothermic Preserved Donor Corneas in Keratoplasty

Purpose: To determine the prevalence, risk factors and microbial profiles of donor corneal contamination and its association with postoperative infection. Materials and Methods: 1348 hypothermic preserved donor corneas were screened during keratoplasty to assess the impacts of donor age, gender, cause of death and corneal preservation time on the contamination risk. The microbial spectrum and antibiotic sensitivity of causative microorganisms and the prognostic role of corneoscleral rim cultures were analyzed. Results: 111 donor corneas (8.2%) had positive microbial cultures, with 84 contaminated by bacteria, 25 by fungi and 2 by both. Acinetobacter baumannii complex (19.8%) and Candida spp. (9.0%) were the most commonly isolated bacteria and fungi, respectively. Two patients (1.8%) who received contaminated corneal buttons developed postoperative infections. Death due to cardiac disease led to more corneal contaminations than death due to brain disease (odds ratio (OR) = 2.59, P = .009). Longer preservation time was associated with a trend toward increasing contamination rate (from 8.3% to 15.0%). Moreover, fungal-contaminated corneas were preserved longer than bacterial-contaminated corneas (6.6 ± 4.5 versus 10.2 ± 5.4 days, P = .001). Corneas from donors who died from cardiac diseases and trauma showed the highest prevalence of bacterial (10.9%) and fungal (2.6%) contamination, respectively. Antibiotic sensitivity testing revealed that the third-generation fluoroquinolone levofloxacin had high rates of susceptibility to both gram-positive (G+) (60.0%) and gram-negative (G-) (44.6%) bacteria. Conclusions: The causes of donor corneal contamination are multifactorial. The antibiotic resistance rate of contaminating microbes seems to be increasing. Whether antibiotic usage in storage medium and postoperative prophylaxis should be updated accordingly warrants further investigation.

Reappraisal of the suitability of corneas from bacteremic donors for use in corneal transplants

Background

This study examined whether corneas from bacteremic donors could be used for corneal transplant.

Methods

Corneas donated to the National Eye Bank of Taiwan between 1 January 2014 and 30 June 2017 were included in this study. All the corneas had corneoscleral rim cultures during the retrieval process and were hypothermic preserved in the Optisol-GS storage medium. A microbial work-up flow chart was used for the sterility check of all grafts. Bacteremic donors were defined as those whose last blood culture before corneal donation was positive. The microbial contamination rates, the endothelial cell densities, the tissue utility rates and early complications after transplants were compared between the corneas from bacteremic versus non-bacteremic donors.

Results

697 corneas from 356 donors were analysed, 70 of which were from bacteremic donors. The microbial contamination rates of the corneas from bacteremic and non-bacteremic donors (7.1% vs 9.1%)(p=0.30) were close. None of the contaminated corneas grew the same bacterial strains as those from their blood cultures. The corneas from bacteremic donors and non-bacteremic donors have similar endothelial cell densities (2931±297 cells/mm2 vs 2903 ± 470 cells/mm2) (p=0.63). Corneas from bacteremic and non-bacteremic donors shared a similar utility rate (98.6% vs 99.4%)(p=0.41). None of the corneas caused infectious complications after transplants.

Conclusion

Our study showed that corneas from bacteremic and non-bacteremic donors have equally low contamination rates and are of the same quality in terms of endothelial cell density and safety.

Factors influencing the contamination rates of the conjunctival swabs and organ culture media of human donor eyes

This study assessed the influence of donor, environmental, and logistical factors on the contamination rates of the conjunctival swabs and organ culture media of human donor eyes.In total, 1008 conjunctival swabs and 418 organ culture media samples from 504 consecutive human donor eyes were analyzed. Cross-tabulation, chi-squared tests, and Fisher's exact tests were used to assess the influence of the different factors on the contamination rates of the conjunctival swabs and organ culture media.The overall contamination rates were 28.4% for the conjunctival swabs and 1.0% for the organ culture media. A prolonged time between death and the conjunctival swab collection was associated with an increased conjunctival swab contamination rate [odds ratio (OR) = 1.9, 95% confidence interval (CI) = 1.2-3.0, P = .007]. The highest conjunctival swab contamination rate was found in the corneas procured in external institutions (outside the university hospital) (44.1%, OR = 3.6, 95%CI = 1.5-8.4, P = .003). Hospitalization times of 2 to 7 days prior to death were associated with an increased conjunctival swab contamination risk (OR = 2.6, 95%CI = 1.1-5.8, P = .021). However, the sex, age, cause of donor death, differentiation between septic and aseptic donors, differentiation between heart-beating brain-dead multiorgan donors and cadaveric donors, a warmer mean monthly temperature, and death to corneoscleral disc excision time did not significantly increase the conjunctival swab contamination risk. In addition, none of these factors affected the organ culture media contamination risk. Moreover, a positive conjunctival swab did not significantly increase the media contamination risk (P = .08). Surprisingly, the microorganisms causing media contamination were present at 50% of the amount detected on the conjunctival surface of the respective donor eye.A prolonged time between death and the conjunctival swab collection, a hospitalization time of 2 to 7 days prior to death, and corneal collection outside the university hospital seemed to be the main factors responsible for an increased conjunctival swab contamination risk. In addition, our investigation illustrated that a positive conjunctival swab is not a strong indicator for organ culture media contamination. Critical discussion is necessary regarding the validity of conjunctival swabs as prognostic parameters for organ culture media contamination.

New Paradigms for the Study of Ocular Alphaherpesvirus Infections: Insights into the Use of Non-Traditional Host Model Systems

Ocular herpesviruses, most notably human alphaherpesvirus 1 (HSV-1), canid alphaherpesvirus 1 (CHV-1) and felid alphaherpesvirus 1 (FHV-1), infect and cause severe disease that may lead to blindness. CHV-1 and FHV-1 have a pathogenesis and induce clinical disease in their hosts that is similar to HSV-1 ocular infections in humans, suggesting that infection of dogs and cats with CHV-1 and FHV-1, respectively, can be used as a comparative natural host model of herpesvirus-induced ocular disease. In this review, we discuss both strengths and limitations of the various available model systems to study ocular herpesvirus infection, with a focus on the use of these non-traditional virus-natural host models. Recent work has demonstrated the robustness and reproducibility of experimental ocular herpesvirus infections in dogs and cats, and, therefore, these non-traditional models can provide additional insights into the pathogenesis of ocular herpesvirus infections.