Sterility screening of platelet concentrates: questioning the optimal test strategy

Bordetella holmesii Contamination of Platelet Concentrates: Revisiting the Definition of a Positive Culture

Bacterial contamination remains the most important infectious risk of platelet transfusion. After an initially positive result, a second test is performed on the blood products and the initial culture bottle to confirm the contamination. Based on the blood center's decision algorithm used, results can be either confirmed negative, positive, or indeterminate, or be unconfirmed or discordant. Here, we report the first cases of platelet concentrates contaminated with Bordetella holmesii The in vitro growth characteristics of this unusual contaminant in platelet concentrate were investigated. Two B. holmesii strains isolated from platelet concentrates, as well as a control strain (Serratia marcescens), were spiked into platelet concentrates (PCs) at 1 and 10 CFU/ml. PCs were stored at 20 to 24°C under agitation. Samples were collected on days 2, 3, 4, and 7 for colony count and for bacterial screening using the BacT/Alert 3D system. Two PCs were detected as being positive for B. holmesii However, recultures were negative. In vitro, B. holmesii did not grow but remained detectable in PCs. Its viability diminished rapidly in contact with human plasma. Upon screening using the BacT/Alert 3D system, the majority of products spiked with B. holmesii were negative. This is the first description of PCs contaminated with B. holmesii This bacterium survives in blood products and remains dormant at low concentrations in blood products stored at room temperature, thus making difficult its detection with the BacT/Alert 3D system. The present definition of a true-positive culture of PCs may be overly restrictive for certain bacterial strains.

Detection of bacterial contamination in platelet concentrates from Brazilian donors by molecular amplification of the ribosomal 16S gene

OBJECTIVE

The aim of our work was to establish a semi-automated high-throughput DNA amplification method for the universal screening of bacteria in platelet concentrates (PCs).

BACKGROUND

Among cases of transfusion transmission of infectious agents, bacterial contamination ranks first in the number of events, morbidity and mortality. Transmission occurs mainly by transfused PCs. Automated culture is adopted by some blood banks for screening of bacterial contamination, but this procedure is expensive and has a relatively long turnaround time.

METHODS

PCs were spiked with suspensions of five different bacterial species in a final concentration of 1 and 10 colony-forming units (CFU) per millilitre. After incubation, the presence of bacteria was investigated by real-time polymerase chain reaction (PCR) and by the Enhanced Bacterial Detection System (eBDS, Pall) assay as a reference method. Real-time PCR amplification was performed with a set of universal primers and probes targeting the 16S rRNA gene. Co-amplification of human mitochondrial DNA served as an internal control.

RESULTS

Using the real-time PCR method, it was possible to detect the presence of all bacterial species tested with an initial concentration of 10 CFU mL^-1 24 h after contamination, except for Staphylococcus hominis. The PCR assay also detected, at 24 h, the presence of Serratia marcescens and Enterobacter cloacae with an initial concentration of 1 CFU mL^-1 .

CONCLUSIONS

The real-time PCR assay may be a reliable alternative to conventional culture methods in the screening of bacterial contamination of PCs, enabling bacterial detection even with a low initial concentration of microorganisms.

Detection of the relatively slow-growing Propionibacterium acnes in seven matrices of blood components and advanced therapeutical medicinal products

BACKGROUND

Relatively slow-growing bacteria like Propionibacterium acnes represent a challenge for quality control investigations in sterility release testing of blood components and advanced therapeutic medicinal products (ATMPs).

METHODS

A convenient validation with 7 matrices was performed using buffy coat, stem cells, islet cells, natural killer cells, red blood cells, platelets and plasma in the microbial detection system Bact/Alert^®3D incubator. All matrix samples were spiked twofold with Propionibacterium acnes with approximately 50 colony forming units (CFUs) per bottle in iAST and iNST culture bottles for 14days using a multishot bioball. Additionally, the stem cell preparations were also incubated in iFAplus and iFNplus culture bottles, which include neutralizing polymers.

RESULTS

The Bact/Alert^®3D-System detected Propionibacterium acnes in anaerobic culture bottles in buffy coat [3.3 d (=positive signal day to detection as mean value)], red blood cells [3.2 d], platelets [3.3], plasma [3.7 d], natural killer cells [3.3 d] and islet cells [4.9 d], resp. No growth of Propionibacterium was found in autologous stem cells using iAST and iNST culture bottles. However, Propionibacterium was safely detected in the iFNplus culture bottle with polymers in the stem cell matrix. A successful validation of media was performed.

CONCLUSIONS

Our study shows that Bact/Alert^®3D-System safely detects the relatively slow-growing bacterium Propionibacterium acnes in different matrices in a practical way except stem cells. Using the iFNplus culture bottle for stem cell products positive signals were observed.

Routine bacterial screening of platelet concentrates by flow cytometry and its impact on product safety and supply

BACKGROUND AND OBJECTIVES

Bacterial contamination represents the major infectious hazard associated with transfusion of platelet concentrates (PCs). As bacterial screening of PCs is not mandatory in Germany, the BactiFlow flow cytometry test has been introduced as a rapid detection method to increase product safety.

MATERIALS AND METHODS

During a period of 25 months, a total of 34 631 PCs (26 411 pooled and 8220 apheresis-derived PCs) were tested at the end of day 3 of their shelf life using the BactiFlow system. PCs initially reactive in BactiFlow testing and expired PCs not reactive in BactiFlow on day 3 were also investigated by the BacT/ALERT system and by microbiological cultivation in order to identify the contaminating bacterial species and to confirm reactive BactiFlow results.

RESULTS

Two hundred and twenty-eight PCs (0.7%) had an initially reactive result, 24 of them remained reactive in a second test run. Out of these reproducible reactive BactiFlow results, 12 could not be verified by parallel BacT/ALERT culturing, resulting in a confirmed false-positive rate of 0.03%. The bacterial species were identified as S. aureus, S. epidermidis, S. dysgalactiae ssp. equisimilis and B. cereus. In 10 out of 9017 expired PCs (0.11%), a confirmed-positive result was obtained in the BacT/ALERT system which had a negative result in the BactiFlow system.

CONCLUSION

Testing of PCs by BactiFlow was successfully implemented in our blood donation service and proved sufficient as a rapid and reliable screening method. False reactive results are in an acceptable range since the transfusion of 12 bacterially contaminated PCs was prevented.

Pathogen inactivation efficacy of Mirasol PRT System and Intercept Blood System for non-leucoreduced platelet-rich plasma-derived platelets suspended in plasma

BACKGROUND AND OBJECTIVES

This study was conducted to evaluate the efficacy of pathogen inactivation (PI) in non-leucoreduced platelet-rich plasma-derived platelets suspended in plasma using the Mirasol PRT System and the Intercept Blood System.

METHODS

Platelets were pooled using the Acrodose PL system and separated into two aliquots for Mirasol and Intercept treatment. Four replicates of each viral strain were used for the evaluation. For bacteria, both low-titre (45-152 CFU/unit) inoculation and high-titre (7·34-10·18 log CFU/unit) inoculation with two replicates for each bacterial strain were used. Platelets with non-detectable bacterial growth and platelets inoculated with a low titre were stored for 5 days, and culture was performed with the BacT/ALERT system.

RESULTS

The inactivation efficacy expressed as log reduction for Mirasol and Intercept systems for viruses was as follows: human immunodeficiency virus 1, ≥4·19 vs. ≥4·23; bovine viral diarrhoea virus, 1·83 vs. ≥6·03; pseudorabies virus, 2·73 vs. ≥5·20; hepatitis A virus, 0·62 vs. 0·76; and porcine parvovirus, 0·28 vs. 0·38. The inactivation efficacy for bacteria was as follows: Escherichia coli, 5·45 vs. ≥9·22; Staphylococcus aureus, 4·26 vs. ≥10·11; and Bacillus subtilis, 5·09 vs. ≥7·74. Postinactivation bacterial growth in platelets inoculated with a low titre of S. aureus or B. subtilis was detected only with Mirasol.

CONCLUSION

Pathogen inactivation efficacy of Intercept for enveloped viruses was found to be satisfactory. Mirasol showed satisfactory inactivation efficacy for HIV-1 only. The two selected non-enveloped viruses were not inactivated by both systems. Inactivation efficacy of Intercept was more robust for all bacteria tested at high or low titres.

Bacterial safety of cell-based therapeutic preparations, focusing on haematopoietic progenitor cells

Bacterial safety of cellular preparations, especially haematopoietic progenitor cells (HPCs), as well as advanced therapy medicinal products (ATMPs) derived from stem cells of various origins, present a challenge for physicians, manufacturers and regulators. The article describes the background and practical issues in this area and illustrates why sterility of these products cannot currently be guaranteed. Advantages and limitations of approaches both for classical sterility testing and for microbiological control using automated culture systems are discussed. The review considers novel approaches for growth-based rapid microbiological control with high sensitivity and faster availability of results, as well as new methods for rapid bacterial detection in cellular preparations enabling meaningful information about product contamination within one to two hours. Generally, however, these direct rapid methods are less sensitive and have greater sampling error compared with the growth-based methods. Opportunities for pyrogen testing of cell therapeutics are also discussed. There is an urgent need for development of novel principles and methods applicable to bacterial safety of cellular therapeutics. We also need a major shift in approach from the traditional view of sterility evaluation (identify anything and everything) to a new thinking about how to find what is clinically relevant within the time frame available for the special clinical circumstances in which these products are used. The review concludes with recommendations for optimization of microbiological control of cellular preparations, focusing on HPCs.

Evaluation of an ethidium monoazide-enhanced 16S rDNA real-time polymerase chain reaction assay for bacterial screening of platelet concentrates and comparison with automated culture

BACKGROUND

Culture-based systems are currently the preferred means for bacterial screening of platelet (PLT) concentrates. Alternative bacterial detection techniques based on nucleic acid amplification have also been developed but these have yet to be fully evaluated. In this study we evaluate a novel 16S rDNA polymerase chain reaction (PCR) assay and compare its performance with automated culture.

STUDY DESIGN AND METHODS

A total of 2050 time-expired, 176 fresh, and 400 initial-reactive PLT packs were tested by real-time PCR using broadly reactive 16S primers and a "universal" probe (TaqMan, Invitrogen). PLTs were also tested using a microbial detection system (BacT/ALERT, bioMérieux) under aerobic and anaerobic conditions.

RESULTS

Seven of 2050 (0.34%) time-expired PLTs were found repeat reactive by PCR on the initial nucleic acid extract but none of these was confirmed positive on testing frozen second aliquots. BacT/ALERT testing also failed to confirm any time-expired PLTs positive on repeat testing, although 0.24% were reactive on the first test. Three of the 400 "initial-reactive" PLT packs were found by both PCR and BacT/ALERT to be contaminated (Escherichia coli, Listeria monocytogenes, and Streptococcus vestibularis identified) and 14 additional packs were confirmed positive by BacT/ALERT only. In 13 of these cases the contaminating organisms were identified as anaerobic skin or oral commensals and the remaining pack was contaminated with Streptococcus pneumoniae.

CONCLUSION

These results demonstrate that the 16S PCR assay is less sensitive than BacT/ALERT and inappropriate for early testing of concentrates. However, rapid PCR assays such as this may be suitable for a strategy of late or prerelease testing.

Detection of bacterial contamination in platelet concentrates using flow cytometry and real-time PCR methods

Despite considerable advances in the safety of blood components based on the application of highly sensitive and specific screening methods to minimize the viral infection risk, the prevention of transfusion-associated bacterial infection remains a major challenge in transfusion medicine. In particular, platelet concentrates represent the greatest infectious risk of transfusion-transmitted bacterial sepsis. The detection of bacterial contamination in platelet concentrates has been implemented in several blood services as a routine quality control testing. Although culture is likely to remain the gold standard method of detecting bacterial contamination, the use of rapid methods is likely to increase and play an important role in transfusion medicine in the future. In particular, flow cytometric methods and nucleic acid amplification techniques are powerful tools in bacterial screening assays. Compared to culture-based methods, the combination of high sensitivity and specificity, low contamination risk, ease of performance, and speed has made those technologies appealing alternatives to conventional culture-based testing methods.

Application of reticulated platelets to transfusion management during autologous stem cell transplantation

BACKGROUND

The immature (or reticulated) platelet fraction (IPF) is rich in nucleic acids, especially RNA, and can be used as a predictive factor for platelet recovery in platelet immunomediated consumption or in postchemotherapy myelosuppression. Our aim was to determine if transfusions with IPF-rich solutions, during autologous peripheral blood stem cell transplantation, reduce the occurrence of bleeding and hemorrhagic complications.

PATIENTS AND METHODS

Transfusions were administered to 40 children, affected with hematological pathologies, who underwent autologous peripheral hematopoietic progenitor cell transplantation. There were two groups of 20 patients, one group treated with IPF-poor and the other with IPF-rich solutions. In the two groups, the conditioning regimen was the same for the same pathology (hematological pathologies: 14 acute lymphoblastic leukemia; twelve acute myelocytic leukemia; four non-Hodgkin's lymphoma; two Hodgkin's lymphoma; eight solid tumors). A new automated analyzer was used to quantify the IPF: the XE2100 (Sysmex, Kobe, Japan) blood cell counter with upgraded software.

RESULTS

The 20 patients who received solutions with a high percentage of IPF (3%-9% of total number of infused platelets) required fewer transfusions than the 20 patients who received transfusions with a low percentage of IPF (0%-1% of total number of infused platelets): 83 versus 129 (mean of number of transfusions 4.15 versus 6.45) and a significant difference was found between the two groups by using the Mann-Whitney test (P < 0.001). The prophylactic transfusions decreased from three to two per week. There was only one case of massive hemorrhage.

CONCLUSION

The use of IPF solutions reduces the number of transfusions and bleedings after peripheral blood stem cell transplantation in pediatric patients.

Bacterial contamination in platelets: incremental improvements drive down but do not eliminate risk

BACKGROUND

Bacterial contamination of platelet components (PCs) remains an important cause of transfusion-associated infectious risk. In 2004, Canadian Blood Services (CBS) implemented bacterial testing of PCs using the BacT/ALERT 3D system (bioMérieux). This system has been validated and implemented and continuous monitoring of culture rates allows gathering of data regarding true and false positives as well as false negatives.

STUDY DESIGN AND METHODS

National data gathered between March 2004 and October 2010 from 12 CBS sites were analyzed to compare bacterial contamination rates across three platelet (PLT) preparation methods: apheresis, buffy coat, and PLT-rich plasma. Data were compared before and after implementation of protocol changes that may affect bacterial detection or contamination rates.

RESULTS

Initial positive rates among the three production methods were significantly different, with apheresis PCs being the highest. The rates of confirmed positives among production methods did not differ significantly (p = 0.668). Increasing sample testing volumes from 4 to 6 mL to 8 to 10 mL significantly increased the rate of initial positives, while confirmed positives increased from 0.64 to 1.63 per 10,000, approaching significance (p = 0.055). Changing the skin disinfection method from a two-step to a one-step protocol did not significantly alter the rate of confirmed positives. During the period of data analysis, eight false-negative cases were reported, with five implicated in adverse transfusion reactions.

CONCLUSION

Bacterial testing of PCs and implementation of improved protocols are incrementally effective in reducing the risk of transfusion of bacterially contaminated PLT concentrates; however, the continued occurrence of false-negative results means the risk has not been eliminated.

The Pan Genera Detection immunoassay: a novel point-of-issue method for detection of bacterial contamination in platelet concentrates

Bacterial contamination of platelet concentrates (PCs) still represents an ongoing risk in transfusion-transmitted sepsis. Recently the Pan Genera Detection (PGD) system was developed and FDA licensed for screening of bacterial contamination of PCs directly prior to transfusion. The test principle is based on the immunological detection of lipopolysaccharide (for Gram-negative bacteria) or lipoteichoic acid (for Gram-positive bacteria). In the present study we analyzed the applicability of this method with regard to detection limit, practicability, implementation, and performance. PCs were spiked with Staphylococcus aureus, Bacillus subtilis, and five different Klebsiella pneumoniae strains, as well as eight different Escherichia coli strains. The presence of bacteria was assessed by the PGD immunoassay, and bacteria were enumerated by plating cultures. Application of the PGD immunoassay showed that it is a rapid test with a short hands-on time for sample processing and no demand for special technical equipment and instrument operation. The lower detection limits of the assay for Gram-positive bacteria showed a good agreement with the manufacturer's specifications (8.2 × 10(3) to 5.5 × 10(4) CFU/ml). For some strains of K. pneumoniae and E. coli, the PGD test showed analytical sensitivities (>10(6) CFU/ml) that were divergent from the designated values (K. pneumoniae, 2.0 × 10(4) CFU/ml; E. coli, 2.8 × 10(4) CFU/ml). Result interpretation is sometimes difficult due to very faint bands. In conclusion, our study demonstrates that the PGD immunoassay is an easy-to-perform bedside test for the detection of bacterial contamination in PCs. However, to date there are some shortcomings in the interpretation of results and in the detection limits for some strains of Gram-negative bacteria.

Novel flow cytometry-based screening for bacterial contamination of donor platelet preparations compared with other rapid screening methods

BACKGROUND

Bacterial contamination is the major infectious hazard associated with transfusion of platelet preparations (PLTs). Routine testing for bacterial contamination in PLTs has become common, but transfusion-transmitted bacterial sepsis has not been eliminated. Here, we describe a novel flow cytometry-based method for point-of-issue screening of PLTs for bacterial contamination.

METHODS

We used the BactiFlow flow cytometer to detect and count bacteria based on esterase activity in viable cells. We compared the assay to incubation (BacT/Alert culture system) and rapid nucleic acid-based or immunoassay (reverse transcription PCR, Pan Genera Detection) methods.

RESULTS

We established a protocol for bacterial screening of PLTs consisting of enzymatic digestion and centrifugal filtration for the elimination of viable platelets and selective labeling of bacteria with fluorescent esterase substrate (ChemChrome V23). Results from the BactiFlow showed an excellent correlation (r = 0.9923 E. coli, r = 0.9736 S. epidermidis) to traditional plate count results. The lower detection limit of the assay was determined to be 150 CFU/mL, and the time to result was <1 h.

CONCLUSIONS

Our study demonstrates that BactiFlow flow cytometry is suitable for rapid screening of PLTs for bacterial contamination and fulfils the requirements for a point-of-issue testing of PLTs with acceptable time to result, specificity, sensitivity, and cost.