High incidence of pathogenic microorganisms in bone allografts explanted in the morgue

Effects of SCCO2, Gamma Irradiation, and Sodium Dodecyl Sulfate Treatments on the Initial Properties of Tendon Allografts

Sterile and decellularized allograft tendons are viable biomaterials used in reconstructive surgeries for dense connective tissue injuries. Established allograft processing techniques including gamma irradiation and sodium dodecyl sulfate (SDS) can affect tissue integrity. Supercritical carbon dioxide (SCCO₂) represents a novel alternative that has the potential to decellularize and sterilize tendons with minimized exposure to denaturants, shortened treatment time, lack of toxic residues, and superior tissue penetration, and thus efficacy. This study attempted to develop a single-step hybrid decellularization and sterilization protocol for tendons that involved SCCO₂ treatment with various chemical additives. The processed tendons were evaluated with mechanical testing, histology, scanning electron microscopy (SEM), and Fourier-transform infrared (FTIR) spectroscopy. Uniaxial mechanical testing showed that tendons treated with SCCO₂ and additive NovaKill^TM Gen2 and 0.1% SDS had significantly higher (p < 0.05) ultimate tensile stress (UTS) and Young's modulus compared to gamma-irradiated and standard-SDS-treated tendons. This was corroborated by the ultrastructural intactness of SCCO₂-treated tendons as examined by SEM and FTIR spectroscopy, which was not preserved in gamma-irradiated and standard SDS-treated tendons. However, complete decellularization was not achieved by the experimented SCCO₂-SDS protocols used in this study. The present study therefore serves as a concrete starting point for development of an SCCO₂-based combined sterilization and decellularization protocol for allograft tendons, where additive choice is to be optimized.

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.

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.

Postmortem angiography using femoral cannulation and postmortem microbiology

Despite the undeniable advantages of postmortem angiography, numerous questions have arisen concerning the influence that the injected contrast media may exercise on biological fluids and tissues collected for toxicological and biochemical investigations. Moreover, cardiac blood for microbiological investigations cannot be obtained post-angiography. In this study, we examined whether the peripheral blood collected prior to postmortem angiography, using percutaneous access to femoral vessels after skin surface disinfection, could be suitable for microbiological investigations when postmortem angiography with femoral vessel cannulation is also performed. A total of 66 cases were included in the study and were divided into two subgroups (angiography and bacteriology group, 33 cases and control group, 33 cases). Autopsies, histology, toxicology, bacteriology, and biochemical investigations (procalcitonin, C-reactive protein, interleukin-6, and soluble triggering receptors expressed on myeloid cells type 1) were performed in all cases. No statistically significant differences between the two groups were noted, and identified category distribution (death unrelated to infection, true infection, false positive, and undetermined) was rather similar in both studied populations. These preliminary results suggest that postmortem angiography using a femoral approach does not constitute an impediment to the collection of peripheral blood for microbiology and vice versa. Moreover, the use of femoral blood for microbiology does not lead to an increased risk of doubtful results.

Evaluation of two types of swabs for sampling allograft musculoskeletal tissue

BACKGROUND

Allograft musculoskeletal tissue is commonly sampled by a swab for bioburden screening. To determine if bioburden recovery could be improved at the pre-analytical stage, two swab systems were evaluated: the Amies gel swab and the ESwab.

METHODS

In vitro studies were performed to determine the recovery of each swab system with <100 colony-forming unit of challenge organisms using inoculated swabs and by sampling inoculated femoral heads. The standard culture protocol used in this laboratory was also evaluated after sampling of inoculated femoral heads. A prospective study was performed with both swab systems used in parallel to sample cadaveric allograft musculoskeletal tissue.

RESULTS

The challenge organisms could be recovered from the in vitro inoculated studies. The standard culture protocol in this laboratory recovered all challenge organisms from both swab systems. One hundred and six paired Amies and ESwabs were collected from eight cadaveric donors with skin commensals the predominant isolates.

CONCLUSIONS

The sampling of an inoculated femoral head was included to reflect routine swab sampling practice as was the inclusion of the standard method used in this laboratory. This appears to be the first study to compare Amies gel swabs with ESwabs to sample allograft femoral heads and in a prospective study with cadaveric allograft musculoskeletal tissue. Other comparative studies of swab systems have used a much higher inoculum to mimic an infection; however, sepsis is an exclusion criterion for allograft donors. It was found that the Amies gel swab and ESwab are both suitable sampling devices for bioburden testing of allograft musculoskeletal tissue.

Broth versus solid agar culture of swab samples of cadaveric allograft musculoskeletal tissue

As part of the donor assessment protocol, bioburden assessment must be performed on allograft musculoskeletal tissue samples collected at the time of tissue retrieval. Swab samples of musculoskeletal tissue allografts from cadaveric donors are received at the microbiology department of the South Eastern Area Laboratory Services (Australia) to determine the presence of bacteria and fungi. This study will review the isolation rate of organisms from solid agar and broth culture of swab samples of cadaveric allograft musculoskeletal tissue over a 6-year period, 2006-2011. Swabs were inoculated onto horse blood agar (anaerobic, 35 °C) and chocolate agar (CO2, 35 °C) and then placed into a cooked meat broth (aerobic, 35 °C). A total of 1,912 swabs from 389 donors were received during the study period. 557 (29.1 %) swabs were culture positive with the isolation of 713 organisms, 249 (34.9 %) from solid agar culture and an additional 464 (65.1 %) from broth culture only. This study has shown that the broth culture of cadaveric allograft musculoskeletal swab samples recovered a greater amount of organisms than solid agar culture. Isolates such as Clostridium species and Staphylococcus aureus would not have been isolated from solid agar culture alone. Broth culture is an essential part of the bioburden assessment protocol of swab samples of cadaveric allograft musculoskeletal tissue in this laboratory.

Micro-organisms isolated from cadaveric samples of allograft musculoskeletal tissue

Allograft musculoskeletal tissue is commonly used in orthopaedic surgical procedures. Cadaveric donors of musculoskeletal tissue supply multiple allografts such as tendons, ligaments and bone. The microbiology laboratory of the South Eastern Area Laboratory Services (SEALS, Australia) has cultured cadaveric allograft musculoskeletal tissue samples for bacterial and fungal isolates since 2006. This study will retrospectively review the micro-organisms isolated over a 6-year period, 2006-2011. Swab and tissue samples were received for bioburden testing and were inoculated onto agar and/or broth culture media. Growth was obtained from 25.1 % of cadaveric allograft musculoskeletal tissue samples received. The predominant organisms isolated were coagulase-negative staphylococci and coliforms, with the heaviest bioburden recovered from the hemipelvis. The rate of bacterial and fungal isolates from cadaveric allograft musculoskeletal tissue samples is higher than that from living donors. The type of organism isolated may influence the suitability of the allograft for transplant.

Analysis of predisposing factors for contamination of bone and tendon allografts

Bone and tissue allografts are widely used in transplantation. The increasing demand for safe allografts must be met, while minimizing disease transmission. We analysed the incidence and potential risk factors of allograft contamination and the effectiveness of disinfection, by reviewing 22 years of tissue bank activity and 474 donor procurements. We also compared different disinfection procedures used over the 22 years. The overall contamination rate was 10.1%. Risk factors were related to the donor or procurement method. Immediate culture at the tissue recovery site diminished the rate of false positives by reducing later sample manipulation. High-virulence allograft contamination was mainly related to donor factors, while low-virulence contamination was related to procurement methods. Analysis of donor-related risk factors showed no statistical differences for age, sex, or cause of death. An intensive care unit stay was associated with less contamination with high-virulence microbes. Procurement in a setting other than an operating theatre was associated with higher contamination rate. Team experience reduced contamination. Pelvic and tendon allografts were most frequently contaminated. Proper disinfection considerably reduced the contamination rate to 3.6%. We conclude that procurement must be performed under aseptic conditions, with short delays, and by trained personnel. Grafts should be disinfected and packed as soon as possible.

Fungal culture of musculoskeletal tissue: what's the point?

There have not been any studies that review the prevalence of fungal isolates using selective media from samples of banked musculoskeletal tissue retrieved from living and cadaveric donors. A total of 2,036 swab and 2,621 biopsy samples of musculoskeletal tissue from tissue banks were received from the 1st August 2008 till 31st December 2010. Routine culture for fungi using selective media with a prolonged incubation period failed to demonstrate a greater prevalence of fungal isolates than by using non-selective culture media alone. Using selective culture fungi were recovered from only two Sabouraud agar plates (0.1%) but not from non-selective media. During the same period fungi were isolated from three graft samples cultured in non-selective broth media only (0.1%). There was no correlation of fungal isolates from selective or non-selective media inoculated at the same time nor from multiple graft samples collected from the same donor supporting the possibility of an exogenous source for fungal isolates rather than an endogenous source.

Long-term outcome of total hip replacement in patients with or without femoral head contamination

PURPOSE

To compare long-term outcomes of total hip replacement (THR) in patients with or without contamination of the femoral head.

METHODS

After a mean period of 12 (range, 8-17) years, 104 female and 71 male THR patients aged 47 to 96 (mean, 77) years were reassessed via a self-administered questionnaire, and 25 other THR patients were reassessed by review of case notes. The questionnaires comprised the 12-item Oxford hip score and the European Quality Of Life (EuroQOL). 87 and 88 patients had positive and negative cultures in the donated femoral heads, respectively. The 2 groups were compared with respect to the Oxford hip score, the EuroQOL, and rates of complication and revision surgery.

RESULTS

Long-term outcomes of THR patients with or without femoral head contamination were not significantly different. Respectively, the mean Oxford hip scores were 36 and 39 (p=0.4); 16 and 14 patients had the maximum score of 48; 2 and 3 patients scored <10 (mostly owing to aseptic loosening). The respective mean visual analogue scale score of the EuroQOL were 65 and 73 (p=0.07); only the dimension of self care was significantly different between groups (p=0.04). Respectively, 14 and 12 patients had complications (16% vs. 15%, χ²=0.05, p=0.8), whereas 11 and 5 patients had revision surgery (13% vs. 6%, χ²=2.2, p>0.1).

CONCLUSION

Microbiological screening of donated femoral heads plays no role in predicting long-term failure of THR in the donors.

Antimicrobial susceptibility of coagulase-negative staphylococci on tissue allografts and isolates from orthopedic patients

Allograft infection occurs at a rate not different from that of similar procedures with large allografts or sterilized prosthetic devices and is usually caused by coagulase-negative staphylococci (CNS). CNS are feared for their limited antimicrobial susceptibility. We aimed at investigating this risk. CNS were isolated from 260 of 1461 allograft tissue grafts and compared with 384 consecutive clinical isolates from a general orthopedic population (258 patients). The CNS were identified and examined for their susceptibility to nine antibiotics used in routine practice. Staphylococcus epidermidis was the most commonly identified (35%) and the most resistant species of the allograft isolates. Comparing the overall antibiotic susceptibility patterns, clinical pathogens were significantly more resistant to six of the nine antibiotics (p < 0.01), namely penicillin, oxacillin, erythromycin, clindamycin, ofloxacin, and gentamicin. In conclusion, massive allograft infection is a well-known life-threatening surgical risk. However, we did demonstrate that allograft-related in contrast to orthopedic clinics-related CNS, are susceptible to commonly used first and second line antibiotics.

Bacterial infection transmitted by human tissue allograft transplantation

Bacterial contamination of tissue allografts obtained from cadaveric donors has been a serious cause of morbidity and mortality in recipients. Recent cases of fatal and nonfatal bacterial infections in recipients of contaminated articular cartilage (distal femur) and tendon allografts have called attention to the importance of avoiding tissue donors suspected of carrying infectious disease, of not processing donated tissue carrying virulent bacteria, the occurrence of falsely negative final sterility tests, and the need to sterilize tissues. These cases demonstrated that contamination can arise from an infected donor, during tissue removal from cadaveric donors, from the processing environment, and from contaminated supplies and reagents used during processing. Final sterility testing can be unreliable, especially when antibiotics remain on tissues. There is an increasing need for control of microbial contamination in tissue banks, and sterilization of tissue allografts should be recommended whenever possible.

Limitations of bone harvesting from organ donors in Poland

The demand for organ transplantations greatly exceeds the number of organ donors (OD) and it is likely that this discrepancy will continue. There is a continuously growing demand for biostatic allogenic bone transplantation mostly for orthopedic reconstructions. The bone material is predominantly harvested during postmortem examinations in forensic medicine departments. The collected amounts are not enough so the material need to be acquired from other sources. Bone collecting from OD seems to be the optimal solution. Between January 2000 and December 2005, 1,883 out of 2,601 organ donors fulfilled the criteria for bone donation, but only 42 bone harvesting (BH) were performed being only 2.22% of all suitable cases. The main reasons for so few bone procurements were: lack of acceptance of bone procurement by relevant part of donors' families, insufficient cooperation between tissue banks and transplantation teams, lack of equipment for BH, and no experience in bone procurement.

Is retrieval of bone material from multiorgan donors effective enough to cover demand for biostatic bone tissue grafts in Poland?

In Poland there is growing demand for biostatic allogeneic bone transplantation mostly for traumatologic operations and orthopedic reconstructions. The bone material is primarily harvested during postmortem examinations in forensic and pathology laboratories. Nevertheless, the collected amounts are not sufficient, so that material needs to be acquired from alternative sources, such as multiorgan donors. Between 1998 and 2003, 2331 potential donors were registered by the Transplantation Coordinating Center in Warsaw, which was adjusted to 1794 donors who would have been accepted as donors of the bone tissue. Unfortunately, due to denials from family members and public prosecutors, the sample was only 1416 donors, which would cover about 40% of the clinical orthopedic demand in Poland.

Factors Determining the Contamination of Bone Tissue Procured from Cadaveric and Multiorgan Donors

There is an increasing demand for bone allografts that are widely used in orthopedic reconstructive procedures. The bone tissue may be harvested from two sources: cadavers and multiorgan donors. Providing safe and valuable bone allografts is of paramount importance. Contamination of allografts during bone retrieval seems to be one of the most important problems since pathogenic microorganisms might be responsible for postoperative infections and complications in the healing process. The purpose of our study was to identify all factors contributing to bacteriological contamination of harvested bones. Therefore, we have considered factors such as harvesting environment, explantation techniques, storage and preparation of allografts, number of preceding procurements from the same donor, procurement duration, and time interval between death and tissue procurement. The microbiological evaluation of allografts has been performed by taking cultures from all collected bones. Our study revealed significantly greater contamination rates of bone allografts harvested from morgue than from multiorgan donors. According to this observation, we suggest that orthopedic surgeons should pay particular attention to obtain more bones of the highest quality, personally participating in multiorgan procurements.

Cadaveric allograft microbiology

This study aims to determine the contamination rate of cadaveric bone allograft and blood cultures retrieved from 119 donors within Leicester between 1990 and 2003. A contamination rate of 27% was present, with 120 of 437 bone allografts culturing positive at the time of retrieval. Similarly, a contamination rate of 37% was present, with 40 of 107 blood samples culturing positive. The time interval between death and procurement did not influence blood contamination. Coagulase-negative Staphylococcus was the commonest organism isolated in both blood and bone cultures. One donor had Clostridium grown in their blood culture. The available evidence confirms similar contamination rates with other studies. The majority of organisms isolated were skin commensals with a low rate of contamination of highly pathogenic organisms such as Clostridium.

Cefuroxime, rifampicin and pulse lavage in decontamination of allograft bone

The risk of bacterial infection through allogenic bone transplantation is one of the major problems facing tissue banks. Different screening methods and decontamination procedures are being used to achieve a safe surgical result. The purpose of this study was to investigate the contamination rate in fresh frozen bone allografts after treating them with different decontamination methods. The allografts were contaminated by rubbing on the operating theatre floor for 60 min, after which they were rinsed either with sterile physiological saline, cefuroxime or rifampicin solution or they were washed with low-pressure pulse lavage of sterile physiological saline. Our findings show that low-pressure pulse lavage with sterile saline solution is very effective in removing bacteria from bone allograft, when compared with the antibiotic solutions tested.

Microbiological screening of post-mortem bone donors - two case reports

This study assesses the value of blood cultures in combination with swab culturing techniques in association with bone banking procedures. The results of blood and swab cultures of two postmortem bone donors were compared with procured grafts, cultured in their entirety. In one donor, who died of drowning, three of the 12 entire graft cultures were positive with the same microorganism of high pathogenicity as the blood culture, whilst the swab culture of only one graft was positive. In the second donor, who died from myocardial infarction, four entire cultures were positive with the same organism of high pathogenicity as the blood culture, whilst the swab cultures of three grafts were positive. In both donors identical organisms were cultured from the myocardium of the pulmonary or aortic heart valve. The results confirm the limited sensitivity of swab culturing techniques. Especially micro-organisms inside a graft, disseminated through the bloodstream, can remain unnoticed. Blood cultures seem to provide additional information on micro-organisms that have spread haematogenously pre-mortem and may even provide information on the source from which they have spread.

High-pressure saline washing of allografts reduces bacterial contamination

60 fresh-frozen bone allografts were contaminated on the operating room floor. No bacterial growth was detected in 5 of them after contamination. The remaining 55 grafts had positive bacterial cultures and were processed with three methods: soaking in saline, soaking in antibiotic solution or washing by high-pressure saline. After high-pressure lavage, the cultures were negative in three fourths of the contaminated allografts. The corresponding figures after soaking grafts in saline and antibiotic solution were one tenth and two tenths, respectively. High-pressure saline cleansing of allografts can be recommended because it improves safety by reducing the superficial bacterial bioburden.

Gamma irradiation of human bone allografts alters medullary lipids and releases toxic compounds for osteoblast-like cells

The uncertainties about the transmission of prion proteins from xenogenic grafts prepared from bovine bone has led to the reconsideration of allogenic bone as a grafting material. Allografting is a complementary technique to autografting nowadays when large bone volumes are necessary. Several preparation techniques have been proposed. Fresh-frozen, freeze-dried and gamma irradiation are the most common. However, a large amount of lipids is present in the medullary spaces (near 70% in weight for a human femoral head). They are known to strongly influence the biocompatibility of the bone graft. The exact changes of lipids upon the sterilization and storage processes are poorly known. The aims of the present study were to appreciate the effects of gamma irradiation on medullary lipids and to identify the cytotoxicity of gamma-irradiated bank bone with/without lipid on cultures of osteoblast-like cells. Bone cores from 8 femoral heads retrieved during prosthesis surgery for arthritis were prepared with a drilling trephine. Cores were either sterilized by gamma radiations (25000 gray) or kept frozen until lipid extraction and lipofuschine-like dosage by Folch's method and fluorometric study. Peroxidated lipids appeared 2 to 3-fold higher in the gamma-irradiated cores than in frozen ones. Slices were prepared from bone cores and were transferred on confluent osteoblast-like cell layers (Saos-2). The raw slices (containing lipids) did not induce cell death. On the other hand, cell death was dramatically increased around the gamma-irradiated slices. Defatted slices which had been sterilized by gamma radiations or UV did not induce cell death. Defatting procedures should be added when preparing bone allografts in human bone banks.

A comparative study of blood and bone marrow cultures in cadaveric bone donation

The results of blood cultures taken from cadaveric bone donors were compared with bone marrow and also swab cultures of the procured grafts. In eight of the 95 donors evaluated, pathogenic micro-organisms were detected in the blood sample. In two, identical micro-organisms were cultured from the blood and bone marrow sample whilst the swab cultures were negative. Considering the low sensitivity of the swab culture, the organisms detected in the blood culture were likely to have spread haematogenously and considered to be present in the explanted grafts. Bacteriological screening of bone donors is extremely important since the transmission of micro-organisms via an allograft can lead to serious complications in the recipient. Positive blood cultures provide important information on the presence of pathogenic micro-organisms in grafts obtained from cadaveric bone donors and are therefore essential in deciding whether a graft is bacteriologically acceptable for transplantation.