Bacterial contamination of a cornea tissue bank: implications for the safety of graft engineering

Prevalence of bacteria and fungi in samples of cornea preservation fluid

INTRODUCTION

Recipients of corneal transplants are at risk of healthcare-associated infections, which, apart from other causes of surgical site infections, may also occur as a result of the transfer of infected corneal tissue. In this study we assessed the risk of bacterial and fungal infections based on the results of routine microbiological testing of cornea preservation fluid samples.

MATERIAL AND METHODS

We examined a total of 725 samples of corneal preservation fluid, obtained during a period of 3 years (2011-2013). Corneal preservation fluid samples were cultured and identified in accordance with standard microbiological methods.

RESULTS

The analysis comprised 725 samples of corneal preservation fluid, of which 32 (4.4%) samples tested positively in microbiological cultures. In total, 34 strains of bacteria and fungi were cultured. Gram-positive bacteria, Gram-negative bacteria and fungi comprised 85.3%, 8.8% and 5.9% of these strains, respectively. Analysis of the susceptibility of the cultured bacterial isolates to gentamicin was also performed, as this antibiotic is present in the composition of corneal preservation fluid. Among the cultured bacterial strains, 10 (33.3%) were resistant to gentamicin. None of the 32 patients who received a cornea stored in preservation fluid contaminated with bacteria and/or fungi demonstrated infectious complications in the surgical site within 1 year following cornea transplantation.

CONCLUSIONS

We postulate that perioperative antibiotic prophylaxis in cornea transplant recipients is important in preventing bacterial infections derived from the donor cornea. We believe that the addition of an antifungal agent to commercially available cornea preservation fluids should also be considered.

Microbiological risk assessment in stem cell manipulation

Cell therapy based on the use of human stem cells is more complicated than transfusion or organ transplantation because cells may undergo many additional manipulations due to different treatments for isolation, expansion, differentiation, and other types of biological changes. These manipulations require the approval of regulatory agencies (other than ethical) and the processes must be monitored with more tests than the ones applied for minimally manipulated cells. The clinical safety and efficacy of transplanted cells depend on several factors such as homologous or non-homologous sources, extent of manipulation, and culture conditions. Moreover, the kind of information needed to address these issues may differ depending on whether the cells are to be used for tissue reconstruction or repair, or to recover metabolic functions. Also anatomical site, functional integration as well as duration of therapy, are crucial points that indirectly can influence safety. Many important assays have been suggested for environmental monitoring as well as to standardize microbiological controls in stem cell banks to prevent contamination. In order to guarantee safety two main aspects must be considered: one is related to the source of cells (the donor) and the other is depending on cell collection and processing. In this review we critically analyze the steps of the processes (from collection to banking) and consider the main factors involved in the clinical research (continuously in evolution) by suggesting a standardized facsimile form to use in the laboratory for the assessment of the microbiological risk related to the cell manipulations.

Eye Banking Error: Report of a Donor Cornea with a Soft Contact Lens Left in Place

PURPOSE

To report the first known case of a donor cornea being examined and shipped with a soft contact lens in place.

METHODS

Case Report.

RESULTS

Surgery was cancelled, the two involved eye-banks were notified, and the patient underwent successful keratoplasty 2 days later.

CONCLUSION

Eye banking is essential to the practice of Ophthalmology. Rarely, errors occur despite the strict protocols and procedures that have been instituted over the years. These errors force us to reevaluate and update those policies as technology rapidly advances. We present here the first reported case of donor ocular tissue being examined and then shipped with a contact lens on the cornea. It is possible that there are other errors that are not published. It behooves us to disclose these and to discuss any of these errors openly to allow us to maintain confidence in our local eye banks, and to help us practice the safest medicine possible for our patients.

Bacterial Contamination of Human Organ-Cultured Corneas

PURPOSE

This study was designed to define the risk of contamination of human corneas preserved by the organ-culture method.

METHODS

We examined the microbial contaminations in 3,100 corneoscleral rims cultivated in our eye bank. Microbiologic tests were performed in the preservation medium 5 days after the beginning of cornea cultures and in the last day of culture (21.5 +/- 8.1 days), when the corneas were transferred to the deswelling medium. In 1,029 corneas a microbiologic test also was performed 1 day after the beginning of deswelling procedure.

RESULTS

We found 206 microbial contaminations (6.65% of total) after 5 days and 17 (0.55%) at the end of the preservation period. The total number of contaminated samples during the cornea culture was 223 corresponding to 7.2% of the samples (95% confidence interval, 6.3-8.1). The 1,029 tests performed during the deswelling step disclosed 26 contaminated cornea cultures despite apparent sterility of the medium (2.5%; 95% confidence interval, 1.5-3.5).

CONCLUSIONS

The observation of microbial contaminations in a time close to the transplant (i.e., at the end of the preservation period and in the deswelling step) showed that a fast microbial tests during the deswelling procedure may prevent the grafting of a contaminated cornea. The appearance of bacteria in the deswelling medium despite a negative culture medium suggests that bacteria penetrate the corneal tissues during the culture to be subsequently extruded when the internal fluids move outward.