Decontamination of heart valve and arterial allografts in the European Homograft Bank (EHB): comparison of two different antibiotic cocktails in low temperature conditions

Last twenty-years activity of cardiovascular tissue banking in Barcelona

The Barcelona Tissue Bank was established from the merge of two previous multi-tissue banks. Potential donors are screened by Donor Center staff and multi-tissue retrieval is performed by specialized own teams. Tissue processing and preservation is performed in clean room facilities by specialised personnel. After quality control of both donor and all tissues results, the heart valves and vascular segments are stored until medical request. The aim of this report is to present the cardiovascular tissue activity and retrospectively evaluate the outcomes of the changes performed in last 20 years. Cardiovascular tissue from 4088 donors was received, specifically 3115 hearts and 2095 vascular segments were processed and evaluated. A total of 48% of the aortic valves, 68% of the pulmonary valves and 75% of the vascular segments were suitable for transplant. The main reason for discarding tissue was macroscopic morphology followed by microbiological results, for both valves and arteries. Altogether, 4360 tissues were distributed for transplantation: 2032 (47%) vascular segments, 1545 (35%) pulmonary valves and 781 (18%) aortic valves. The most common indication for aortic valve surgery was the treatment of endocarditis, while for pulmonary valves, it was congenital malformation reconstruction. Vascular segments were mainly used for reconstruction after ischemia. During this period, a number of changes were made with the goal of enhancing tissue quality, safety and efficacy. These improvements were achieved through the use of a new antibiotic cocktail, increasing of donor age criteria and changing the microbiological control strategy.

Human skin processing affects clinical outcome in allograft recipients

Skin allografts represent a milestone in burn patient treatment. However, skin procurement is still burdened by high rates of contamination, and validation procedures have not yet been standardized. In addition, it is not clear if tissue viability affects allograft skin outcomes. In 2120 skin samples from 610 donors, a retrospective analysis was performed to identify donor and procurement variables associated with bacterial contamination and tissue viability. Post-processing contamination was associated significantly with the donor type, cause of death, length of hospitalization, procurement site, surgeon, interval between procurement and banking, and decontamination method. Tissue viability appeared to be negatively associated with freezing. In two series of skin allograft recipients (155 and 195 patients), we evaluated the role of skin characteristics and procurement variables on clinical outcomes. We found that the length of hospitalization was associated significantly with donor age. Procalcitonin and PCR values in allograft recipients were correlated with the decontamination method. No significant associations were observed between tissue viability and clinical outcomes (length of hospitalization, cause of donor death, or inflammatory parameters) after allograft transplantation. In these large case series, we identified donor and procurement variables that may affect allograft skin recipients. The decontamination method appeared to be a critical step for skin allograft requiring better standardization.

Application of Homograft Valved Conduit in Cardiac Surgery

Valved conduits often correct the blood flow of congenital heart disease by connecting the right ventricle to the pulmonary artery (RV-PA). The homograft valved conduit was invented in the 1960s, but its wide application is limited due to the lack of effective sterilization and preservation methods. Modern cryopreservation prolongs the preservation time of homograft valved conduit, which makes it become the most important treatment at present, and is widely used in Ross and other operations. However, homograft valved conduit has limited biocompatibility and durability and lacks any additional growth capacity. Therefore, decellularized valved conduit has been proposed as an effective improved method, which can reduce immune response and calcification, and has potential growth ability. In addition, as a possible substitute, commercial xenograft valved conduit has certain advantages in clinical application, and tissue engineering artificial valved conduit needs to be further studied.

Microbiological assessment of arterial allografts processed in a tissue bank

The transmission of microbial infection through tissue allografts is one of the main risks that must be controlled in tissue banks. Therefore, microbiological monitoring controls and validated protocols for the decontamination of tissues during processing have been implemented. This study is based on the evaluation of data from microbiological cultures of arteries (mainly long peripheral arteries) processed in the tissue bank of Valencia (Spain). Donors' profile, pre- and post-disinfection tissue samples were assessed. The presence of residual antibiotics in disinfected tissues was determined and the antimicrobial potential of these tissues was tested. Our overall contamination rate was 23.69%, with a disinfection rate (after antibiotic incubation) of 87.5%. Most (76.09%) of the microbial contaminants were identified as Gram positive. Arterial allografts collected from body sites affected by prior organ removal showed higher risk of contamination. Only vancomycin was detected as tissue release. The antimicrobial effect on Candida albicans was lower than that for bacterial species. Risk assessment for microbial contamination suggested the donor's skin and the environment during tissue collection as the main sources for allograft contamination. Antibiotic-disinfected arterial allografts showed antimicrobial potential.

Disinfection protocol for human musculoskeletal allografts in tissue banking using hydrogen peroxide 30

Musculoskeletal allografts are used in reconstructive procedures, however, the risk of contamination with potential pathogens is possible, and safe transplantation requires multiple processing considerations. Hydrogen peroxide (H₂O₂) has commonly been used in bone washing because it can remove donor cells and eliminate antigens, pathogens, or cytotoxic agents from the matrix. The aim of this study was to evaluate the quantitative activity of H₂O₂ in a model of bone contamination with a high bacterial load to define the bioburden reduction. Twelve bone disc models were artificially contaminated with Staphylococcus aureus. The bones were treated with a washing process composed by antibiotics, 30% hydrogen peroxide, and 70% alcohol. Tryptic Soy Agar plates were directly inoculated with 100µL of each step of the washing process and colonies were counted in CFU/mL. Scanning electron microscopy was used for bone structural analysis before and after the washing process. After antibiotics, there was a drop of less than 1 log for cancellous bone and almost 1 log for cortical bone. However, after H₂O₂, there as a drop of 3 logs for cortical (p = 0.007), and 2 logs for cancellous bone (p = 0.063). The use of alcohol did not change the bioburden following H₂O₂ in cancellous and cortical bone. Despite the important drop of bacterial load, H₂O₂ was not enough to completely eradicate bacterial with this model of bioburden. H₂O₂ is useful in decontamination, but antibiotics have little activity, and alcohol is useless. The process is useful in decontamination up to 3 logs of bioburden.

Does microbiological contamination of homografts prior to decontamination affect the outcome after right ventricular outflow tract reconstruction?

 

OBJECTIVES

Homografts are often in short supply. Today, European guidelines recommend that all tissues contaminated by any of 18 different bacteria and fungi be discarded before antibiotic decontamination has been conducted. The tissue bank in Lund uses more liberal protocols: It accepts all microbes prior to decontamination except multiresistant microbes and Pseudomonas species. The aim of this study was to analyse the effect of contamination on the long-term outcome and occurrence of endocarditis in recipients.

METHODS

Data were collected on homografts and on recipients of homografts in the right ventricular (RV) outflow tract who were operated on between 1995 and 2018 in Lund. The long-term outcome of recipients was analysed in relation to different types of contamination using Cox proportional hazard regression. The proportion of patients with endocarditis was analysed with the χ2 test.

RESULTS

The study included 509 implanted homografts. Follow-up was a maximum of 24 years and 99% complete. A total of 156 (31%) homografts were contaminated prior to antibiotic decontamination. Homografts contaminated with low-risk microbes had the lowest reintervention rate, but there was no significant difference compared to no contamination [hazard ratio (HR) 1.1, 95% confidence interval (CI) 0.73-1.7] or contamination with high-risk microbes (HR 1.6, 95% CI 0.87-2.8) in the multivariable analysis. There was no significant difference in the proportion of cases of endocarditis during the follow-up period between recipients of homografts contaminated prior to decontamination and recipients of homografts with no contamination (P = 0.83).

CONCLUSIONS

Contamination of homograft tissue prior to decontamination did not show any significant effect on the long-term outcome or the occurrence of endocarditis after implantation in the RV outflow tract. Most contaminated homografts can be used safely after approved decontamination.

Transplantation of cryopreserved human heart valves in Europe: 30 years of banking in Brussels and future perspectives

For over 30 years, our TE has processed, controlled for quality and distributed cryopreserved allograft valves for human application. We present a review of this activity and future perspectives of cardiovascular tissue banking. The donor age and medical/behavioral history are in compliance with the regulations of the EUMS. Allograft morphology and function are evaluated in a class A cleanroom. Tests for viral/bacterial infection, histological control of structure/infection/malignancy and control-rate cryopreservation are performed. A total of 7562 hearts were sent to our TE, whereas 7290 valves (pulmonary, aortic and mitral) were transplanted. The donations increased over time: 1934, 2566 and 3062 hearts were donated during the first, second and third decades (increases of 32.7 and 19.3% during the second and third decades). Likewise, there was a significant increase in transplantations with 2050, 2550 and 2690 valves implanted during the first, second and third decades (24.4 and 5.5% increase during the second and third decades). A total of 4475 pulmonary (61.4%), 2760 aortic (37.9%) and 55 mitral valves (0.7%) were transplanted. Outstanding long-term results in adults and evidence of immune-related deterioration of allografts in neonates and infants were demonstrated. Decellularization was suggested as a solution. One hundred pulmonary and 180 aortic valves were sent for transplantation after decellularization for the ESPOIR and ARISE clinical trials and beyond. The donation and transplantation activity increased progressively. Although cryopreserved valves represent the best substitute for diseased valves, accelerated failure appears after implantation in neonates and infants. The implementation of new technologies, such as decellularization, as a standard procedure for treatment of allograft valves will offer further improvements in allograft quality and increase of durability.

The BD BACTEC FX blood culture system with the gentlemacs dissociator is suitable for sterility testing of heart valve and vascular allografts-A validation study

To present our validation study of the BD BACTEC FX blood culture system for sterility testing of cardiovascular tissues aimed for human application. For operational qualification, we performed temperature mapping of the system, vacuum test using non-inoculated BACTEC vials, and growth promotion tests by injecting contaminant strains into aerobic and anaerobic bottles. For performance qualification, negative control, assessment of method suitability, evaluation of sensitivity limits, control of neutralization of antibiotics in biopsy samples from allografts and tissue toxicity effects, were performed. Tissue samples and transport/cryopreservation solutions were homogenized in GentleMACS Dissociator and injected into BACTEC Plus aerobic and anaerobic vials for incubation at 35 °C for 14 days. Tissues were spiked with aerobic and anaerobic bacteria and fungi. Growth of contaminants appeared in all aerobic and anaerobic vials for Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa; in anaerobic vials for Cutibacterium (Propionibacterium) acnes and Clostridium sporogenes; and only in aerobic vials for Candida albicans and Aspergillus brasiliensis. The majority of bacterial strains were detected within two days (59-100%), exceptionally between 3 and 14 days. In contrast, fungal contaminations were detected within 2, 3-6, 7-10 and after 10 days of incubation in 33.3, 71.6, 96.6 and 99.9% of cases,respectively. Uninhibited growth appeared in the tissue biopsies and homogenized tissues with and without antibiotics and in other solutions. BD BACTEC blood culture system with GentleMACS Dissociator is a rapid and efficient tool for detection of contamination in cardio-vascular tissues aimed for human application.

Evaluation of Sterilization/Disinfection Methods of Fibrous Polyurethane Scaffolds Designed for Tissue Engineering Applications

Sterilization of a material carries the risk of unwanted changes in physical and chemical structure. The choice of method is a challenge-the process must be efficient, without significantly changing the properties of the material. In the presented studies, we analyzed the effect of selected sterilization/disinfection techniques on the properties of nanofibrous polyurethane biomaterial. Both radiation techniques (UV, gamma, e-beam) and 20 minutes' contact with 70% EtOH were shown not to achieve 100% sterilization efficiency. The agar diffusion test showed higher sterilization efficiency when using an antimicrobial solution (AMS). At the same time, none of the analyzed techniques significantly altered the morphology and distribution of fiber diameters. EtOH and e-beam sterilization resulted in a significant reduction in material porosity together with an increase in the Young's modulus. Similarly, AMS sterilization increased the value of Young's modulus. In most cases, the viability of cells cultured in contact with the sterilized materials was not affected by the sterilization process. Only for UV sterilization, cell viability was significantly lower and reached about 70% of control after 72 h of culture.

Audit of homograft valve bank

Introduction

Even today, the search for the ideal cardiac valve continues. With advantages of having superior flow dynamics, avoidance of anticoagulation, and resistance to infection, homograft has been shown to have an edge over conventional prosthetic and bioprosthetic valves. But they suffer from disadvantages of limited availability and durability. Our center operates one of the oldest functioning valve banks in the country. We present our experience with homograft valve banking with antibiotic and cryopreserved homografts spread over a quarter century.

Methods

For donor selection, procurement, sterilization, and preservation, the recommendations of the American Association of Tissue Banks are being followed in accordance with statutory provisions of the Transplantation of Human Organs Act, 1994.

Results

During 25-year period (1993-2017), 777 hearts were procured. Age of the donors ranged from 2 to 60 years and hearts were procured within 24 h of death. A total of 1646 homografts (774 pulmonary, 774 aortic, 60 mitral valves, 20 descending thoracic aortae, and 18 monocusps) were harvested. A total of 546 (32%) homografts were rejected for various reasons. Nine hundred sixty-seven (56.7%) homografts were used in different procedures. Of these, 478 were pulmonary homografts, 425 were aortic homografts, 39 mitral homografts, 18 monocusps, and 7 descending thoracic aorta homografts. One hundred fifty-four (16%) homografts were antibiotic preserved and the rest 813 (84%) were cryopreserved.

Conclusions

It is possible to run a homograft valve bank with minimum costs. Though, cryopreservation is more expensive, it provides an opportunity to store the valves for an indefinite period and maintain an uninterrupted supply of homografts.

Risk factors associated with contamination of allograft valves in a tissue bank

The contamination of the transport solution used in cardiovascular allografts can occur from different sources. Risk factors associated with positive microbiological test of transport solution have not been reported previously. This study aimed to determine the risk factor for contamination of transport solution used in the heart valve allografts stored in a Brazilian tissue bank. This retrospective study was conducted on all donors of cardiovascular allografts stored in a tissue bank from December 2008 to December 2017. Microbiological cultures for aerobic and anaerobic bacteria, fungi/yeasts were carried out in TS. Clinical variables were included. From 1001 transport solution, 52% were contaminated. A total of 770 microorganisms were identified, and Staphylococcus spp. was identified in 248 isolates (32.2%). Skin bacteria from skin microbiota were the most commonly identified microorganisms (Staphylococcus spp., Cutibacterium spp., Corynebacterium spp., and Bacillus spp.), occurring in 49.6%. The presence of a diagnosis of healthcare-associated infection was not associated with skin contamination (odds ratio [OR] 0.62 [0.41-0.94]; p = 0.014). Conditions like fever, use of antibiotics, and leukocytosis were less likely associated with contamination of transport solution. A longer warm ischemic time was associated with higher frequency of contamination. In the multivariable analysis, warm ischemic time was independently associated with contamination, and antibiotic therapy was a factor that decreased the rate of contamination (p < 0.05). Contamination of transport solution is associated with modifiable risk factors, such as warm ischemic time. Measures to minimize contamination should be employed to avoid unnecessary tissue discharges.

Experimental procedures for decontamination and microbiological testing in cardiovascular tissue banks

IMPACT STATEMENT

Sterility testing is a critical issue in the recovery, processing, and release of tissue allografts. Contaminated allografts are often discarded, increasing costs, and reducing tissue stocks. Given these concerns, it is important to determine the most effective methodology for sterility testing. This work provides an overview of microbiological methods for sampling and culturing donor grafts for cardiovascular tissue banking.

Contamination profile in allografts retrieved from multitissue donors: longitudinal analysis

Microbiological contamination of retrieved tissues has become an issue of key importance and is a critical aspect of allograft safety, especially in the case of multi-tissue donations, which frequently become contaminated during retrieval and handling. We analysed contamination in 11,129 tissues with a longitudinal contamination profile for each individual tissue. Specifically, 10,035 musculoskeletal tissues and 1094 cardiovascular tissues were retrieved from a total of 763 multi-tissue donors, of whom 105 heart-beating organ donors and 658 deceased tissue donors. Of the 1955 tissues found to be contaminated after the first decontamination step, 1401 tissues (72%) were contaminated by the same species as the one(s) isolated at retrieval (Time¹) and 554 (28%) by different species. Among the 113 tissues testing positive after the 2nd decontamination (Time³), 36 tissues (32%) were contaminated by the same species detected at Time^l while the contaminating species differed from Time¹ in 77 tissues (68%). The higher the number of contaminating species per tissue the higher the percentage of tissues in which contamination changed over time compared to Time¹. The analysis revealed a 28% incidence of new species in tissues already testing positive after retrieval and of 3.5% of tissues becoming positive after admission to the tissue bank. Of these, coagulase-negative Staphylococcus accounted for over 70% of new contaminations.

Stability analysis of the antibiotic cocktail used by Treviso Tissue Bank Foundation for tissues decontamination

Although careful donor selection reduces tissue contamination, close microbiological control of harvested allografts remains a key task of tissue banks. To guarantee the safety of human tissues for allograft transplantation, a decontamination regimen must be adopted which, as recommended by European guidelines, is active against the majority of microorganisms isolated in tissues. Antibiotic decontamination methods differ from one tissue bank to another in terms of antimicrobial agents, temperature and length of exposure. After identifying the most effective antibiotics against the bacterial strains most commonly isolated in allografts, Treviso Tissue Bank Foundation demonstrated the efficacy of an antibiotic cocktail for tissue decontamination containing Gentamicin, Vancomycin and Meropenem. The aim of this study was to analyse the degradation kinetics of the three antibiotics according to preparation method and use. The results show that only Meropenem is unstable at + 4 °C, while Gentamicin and Vancomycin are valid for over 10 days. We thus established to add Meropenem before the start of the tissue decontamination phase.

Evaluation of allograft decontamination with two different antibiotic cocktails at the Treviso Tissue Bank Foundation

Microbiological contamination of retrieved tissues is a critical aspect of allograft safety and tissue banks must continuously implement decontamination procedures to minimize tissue contamination. In this study we compared the decontamination efficacy of a new antibiotic cocktail (cocktail B: BASE medium with Gentamicin, Meropenem and Vancomycin) with the cocktail previously adopted at Treviso Tissue Bank Foundation (FBTV) (cocktail A: RPMI medium with Ceftazidime, Lincomycin, Polymyxin B and Vancomycin). Two decontamination steps were carried out, the first immediately after retrieval, the second after processing. The contamination rate was calculated before processing (Time 1) and cryopreservation (Time 2) for total tissues, musculoskeletal tissues and cardiovascular tissues, and the bacterial species involved were analyzed. Cocktail A was used to decontaminate 3548 tissues, of which 266 were cardiovascular and 3282 musculoskeletal tissues. For cocktail A, total tissue contamination was 18.6% at Time 1 and 0.9% at Time 2, with 15.7% contaminated musculoskeletal tissues at Time 1 and 0.4% at Time 2, respectively, while cardiovascular tissues were 50% contaminated at Time 1 and 6.4% at Time 2. Cocktail B was used to decontaminate 3634 tissues of which 318 were cardiovascular and 3316 musculoskeletal tissues. For cocktail B, total tissue contamination was 8.6% at Time 1 and 0.2% at Time 2, with 7.6% contaminated musculoskeletal tissues at Time 1 and 0.03% at Time 2, respectively. Contamination of cardiovascular tissues was 20.4% at Time 1 and 1.9% at Time 2. Intergroup and intragroup contamination rates decreased statistically significantly (p<0.05). Our results have shown that cocktail B was more effective than cocktail A in killing bacteria in both cardiovascular and musculoskeletal tissues during the two decontamination cycles.

Analysis of potential factors affecting allografts contamination at retrieval

The microbiological contamination of retrieved tissues has become a very important topic and it is a critical aspect in the safety of allografts, especially from multi-tissue donors whose tissues are frequently contaminated as a consequence of retrieval. We analysed a total of 10,107 tissues, 8178 musculoskeletal and 1929 cardiovascular tissues, retrieved from 978 multi-tissue donors. Of these, 159 heart-beating donors (HBD) were also organ donors, while the remaining 819 non-heart-beating donors (NHBD) were tissue donors only. A multivariate logistic model was used to determine the factors affecting contamination risk during retrieval. In the model, the dependent variable was the presence/absence of contamination while the covariates included were: gender, type of donor, age of donor, cause of death, previous skin donation, cadaver time, number of people attending the retrieval, number of tissues retrieved. Moreover, a second log-linear model was used to determine the number of strains isolated per tissue. Tissue contamination was statistically correlated with gender, type of donor, cadaver time, number of people attending the retrieval and season. In conclusion, to minimize the risk of bacterial contamination, aseptic techniques should be used at retrieval, with the number of retrieval team members kept to a minimum. In addition, cadaver time should be as short as possible and the donor should be refrigerated within a few hours after death.

Evaluation of allograft contamination and decontamination at the Treviso Tissue Bank Foundation: A retrospective study of 11,129 tissues

Microbiological contamination of retrieved tissues has become a very important topic and a critical aspect in the safety of allografts. We have analysed contamination in 11,129 tissues with a longitudinal contamination profile for each individual tissue. More specifically, 10,035 musculoskeletal tissues and 1,094 cardiovascular tissues were retrieved from a total of 763 multi-tissue donors, of whom 105 were heart-beating donors as well as organ donors, while the remaining 658 were non-heart beating donors and tissue donors only. All tissues were decontaminated twice, the first time immediately after retrieval and the second time after processing. Each tissue was submitted to microbiological culture three times, i.e., upon retrieval (Time 1), after the first decontamination (Time 2) and after the second decontamination (Time 3). The contamination rate for musculoskeletal tissues was 52%, 16.2% and 0.5% at Time 1, 2 and 3, respectively. The contamination rate for cardiovascular tissues was 84%, 42% and 6%. More than one strain was simultaneously present in 10.8% of musculoskeletal tissues and 44.6% of cardiovascular tissues. Out of 8,560 non-heart-beating donor musculoskeletal tissues, 4,689 (54.8%), 1,383 (16.2%) and 42 (0.5%) were contaminated at Time 1, Time 2 and Time 3, respectively. Out of 1,475 heart-beating donor musculoskeletal tissues, 522 (35.4%) 113 (7.7%) and 2 (0.1%) tissues were found to be contaminated at Time 1, 2 and 3, respectively. Out of 984 non-heart beating donor cardiovascular tissues, 869 (88.3%), 449 (45.6%) and 69 (7%) proved positive at Time 1, 2 and 3 respectively, while 50 (45.5%) and 10 (9.1%) heart-beating donor cardiovascular tissues were contaminated at Time 1 and 2. No tissue was contaminated at Time 3. Based on our methods, the two-step decontamination approach is mandatory in order to drastically reduce the number of tissues found to be positive at the end of the process.

Tissue recovery practices and bioburden: a systematic review

For successful transplantation, allografts should be free of microorganisms that may cause harm to the allograft recipient. Before or during recovery and subsequent processing, tissues can become contaminated. Effective tissue recovery methods, such as minimizing recovery times (<24 h after death) and the number of experienced personnel performing recovery, are examples of factors that can affect the rate of tissue contamination at recovery. Additional factors, such as minimizing the time after asystole to recovery and the total time it takes to perform recovery, the type of recovery site, the efficacy of the skin prep performed immediately prior to recovery of tissue, and certain technical recovery procedures may also result in control of the rate of contamination. Due to the heterogeneity of reported recovery practices and experiences, it cannot be concluded if the use of other barriers and/or hygienic precautions to avoid contamination have had an effect on bioburden detected after tissue recovery. Qualified studies are lacking which indicates a need exists for evidence-based data to support methods that reduce or control bioburden.

Evaluation of new antibiotic cocktails against contaminating bacteria found in allograft tissues

Contamination of retrieved tissues is a major problem for allograft safety. Consequently, tissue banks have implemented decontamination protocols to eliminate microorganisms from tissues. Despite the widespread adoption of these protocols, few comprehensive studies validating such methods have been published. In this manuscript we compare the bactericidal activity of different antibiotic cocktails at different temperatures against a panel of bacterial species frequently isolated in allograft tissues collected at the Treviso Tissue Bank Foundation, a reference organization of the Veneto Region in Italy that was instituted to select, recover, process, store and distribute human tissues. We were able to identify at least two different formulations capable of killing most of the bacteria during prolonged incubation at 4 °C.

Disinfection of human cardiac valve allografts in tissue banking: systematic review report

Cardiovascular allografts are usually disinfected using antibiotics, but protocols vary significantly between tissue banks. It is likely that different disinfection protocols will not have the same level of efficacy; they may also have varying effects on the structural integrity of the tissue, which could lead to significant differences in terms of clinical outcome in recipients. Ideally, a disinfection protocol should achieve the greatest bioburden reduction with the lowest possible impact on tissue integrity. We conducted a systematic review of methods applied to disinfect cardiovascular tissues. The use of multiple broad spectrum antibiotics in conjunction with an antifungal agent resulted in the greatest reduction in bioburden. Antibiotic incubation periods were limited to less than 24 h, and most protocols incubated tissues at 4 °C, however one study demonstrated a greater reduction of microbial load at 37 °C. None of the reviewed studies looked at the impact of these disinfection protocols on the risk of infection or any other clinical outcome in recipients.

Residual antibiotics in decontaminated human cardiovascular tissues intended for transplantation and risk of falsely negative microbiological analyses

We investigated the presence of antibiotics in cryopreserved cardiovascular tissues and cryopreservation media, after tissue decontamination with antibiotic cocktails, and the impact of antibiotic residues on standard tissue bank microbiological analyses. Sixteen cardiovascular tissues were decontaminated with bank-prepared cocktails and cryopreserved by two different tissue banks according to their standard operating procedures. Before and after decontamination, samples underwent microbiological analysis by standard tissue bank methods. Cryopreserved samples were tested again with and without the removal of antibiotic residues using a RESEP tube, after thawing. Presence of antibiotics in tissue homogenates and processing liquids was determined by a modified agar diffusion test. All cryopreserved tissue homogenates and cryopreservation media induced important inhibition zones on both Staphylococcus aureus- and Pseudomonas aeruginosa-seeded plates, immediately after thawing and at the end of the sterility test. The RESEP tube treatment markedly reduced or totally eliminated the antimicrobial activity of tested tissues and media. Based on standard tissue bank analysis, 50% of tissues were found positive for bacteria and/or fungi, before decontamination and 2 out of 16 tested samples (13%) still contained microorganisms after decontamination. After thawing, none of the 16 cryopreserved samples resulted positive with direct inoculum method. When the same samples were tested after removal of antibiotic residues, 8 out of 16 (50%) were contaminated. Antibiotic residues present in tissue allografts and processing liquids after decontamination may mask microbial contamination during microbiological analysis performed with standard tissue bank methods, thus resulting in false negatives.

Determination of Residual Antibiotics in Cryopreserved Heart Valve Allografts

INTRODUCTION: Cardiovascular allografts are systematically incubated in antibiotics for their decontamination, and the antibiotics are removed before allograft implantation. We studied the occurrence of antibiotic residues in allograft valves. MATHODS: 12 experimental allografts were analyzed in this study. The concentration of the residual antibiotics was determined by high-performance liquid chromatography and the results were expressed as microgram per gram of allograft tissue. RESULTS: The initial analysis showed that only vancomycin HCl and lincomycin HCl were retained in the allograft, whereas no traces of polymyxin B sulfate were detected in the tissue samples. Furthermore, the values found for the antibiotic residues in the extracted solution from the allografts were similar to the initial results: Vancomycin and lincomycin were detected in very low concentrations and no polymyxin B residues were observed. According to the World Health Organization (WHO), the maximum daily doses for vancomycin, lincomycin and pol-ymyxin B are 2.0, 1.8 and 0.4 g, respectively. The thresholds for reporting degradation products are 0.05% for vancomycin and lincomycin and 0.1% for polymyxin B. The residual values for the two detected antibiotics were largely below 0.05%. CONCLUSIONS: Antibiotic residues in the allograft valves do not present any risk for their recipients. Increased allograft resistance to infections is probably due to the retention of antibiotics in the tissue.

Heart valve allograft decontamination with antibiotics: impact of the temperature of incubation on efficacy

Heart valve allografts are typically processed at 4°C in North America, including the step of antibiotic decontamination. In our own experience with heart valve banking, we often observe persistent positive cultures following decontamination at wet ice temperature. We hypothesized that warmer temperatures of incubation might increase the efficacy of the decontamination procedure. In a first series of experiments, 12 different bacterial species were grown overnight, frozen in standardized aliquots and used directly to inoculate antibiotic cocktail aliquots at 10⁵ colony-forming units (CFU)/ml. The antibiotic cocktail contains vancomycin (50 μg/ml), gentamicin (80 μg/ml) and cefoxitin (240 μg/ml) in Dulbecco's Modified Eagle's Medium. Inoculated aliquots were incubated at 4, 22 and 37°C and CFUs were determined at regular intervals up to 24 h post-inoculation. In a second set of experiments, 10 heart valves were spiked with 5000 CFU/ml and incubated with antibiotics at 4 and 37°C for 24 h. The final rinse solutions of these heart valves were filtered and tested for bacterial growth. After 24 h of incubation, CFUs of all 12 bacterial species were reduced by a factor of only one to two logs at 4°C whereas log reductions of 3.7 and 5.0 or higher were obtained at 22 and 37°C, respectively. Most microorganisms, including Staphylococcus epidermidis, Lactococcus lactis lactis and Propionibacterium acnes survived well the 24-h antibiotic treatment at 4°C (< 1 Log reduction). All 10 heart valves that were spiked with microorganisms had positive final rinse solutions after antibiotic soaking at 4°C, whereas 8 out of 10 cultures were negative when antibiotic decontamination was done at 37°C. These experiments show that a wet ice temperature greatly reduces the efficacy of the allograft decontamination process as microorganisms survived well to a 24-h 4°C antibiotic treatment. This could explain the high rate of positive post-processing cultures obtained with our routine tissue decontamination procedure. Increasing the decontamination temperature from 4 to 37°C may significantly reduce the incidence of post-disinfection bacterial contamination of heart valves.

Quality control in homograft valve processing: when to screen for microbiological contamination?

Human donor heart valves remain essential for many reconstructive heart procedures. Heart valve donations are a scarce resource which must be used efficiently and safely. Infection transmission remains a potential risk with homograft valve use. Early experience with homograft valves identified high rates of microbial contamination at collection and initiated the practise of immersion in an antibiotic cocktail. Many centres rely on the microbiology screening after exposure to the antibiotic cocktail. We in our centre accept or reject valves on the basis of the microbiology screening at the time of collection prior to immersion in antibiotic solution. We wanted to compare our rate of valve discard and the rate of microbial contamination at implant with other centres. Valves are collected for the Irish Heart Valve Tissue Bank through partnership between the National Centre for Cardiothoracic Surgery and the Irish Blood Transfusion Service. Valves are collected in a surgical theatre setting and processed in dedicated section of the Irish Blood Transfusion Board. Tissues are screening for microbiology at collection and also at implantation. A total of 564 human heart valves and valve conduits were processed through the service during the study period. 167 (29.6%) were discarded during the processing and storage stages. The major reason for this in 117 cases was unsatisfactory microbiology on initial tissue screening. Repeat screening of accepted valves at the time of implantation identified positive cultures in only 0.9%. Optimal use of these limited resources is clearly important. However recipient safety remains paramount. One-fifth of collected valves are discarded at the processing stage due to positive microbiology screening. This is a higher rate of discard then other centres which reject 5.6-10% due to positive microbiology. However our rate of contamination at time of implant is lower then the 3% rate reported elsewhere. We are satisfied that our current discard rate, although significant, reflects rigorous quality control and the optimal balance between valve availability and patient safety.