Elimination and multiplication of bacteria during preparation and storage of buffy coat-derived platelet concentrates

Growth and Distribution of Bacteria in Contaminated Whole Blood and Derived Blood Components

Introduction

Bacterial contamination of blood products presumably occurs mainly during blood collection, starting from low initial concentrations of 10-100 colony-forming units (CFUs) per bag. As little is known about bacterial growth behavior and distribution in stored whole blood (WB) and WB-derived blood products, this study aims to provide data on this subject.

Methods

WB units were inoculated with transfusion-relevant bacterial species (Acinetobacter baumannii, Bacillus cereus, Escherichia coli, Klebsiella pneumoniae, Listeria monocytogenes, Pseudomonas fluorescens, Serratia marcescens, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus dysgalactiae, Streptococcus pyogenes, Yersinia enterocolitica; n = 12 for each species), stored for 22-24 h at room temperature, and then centrifuged for separation into plasma, red blood cells (RBCs), and buffy coats (BCs). The latter were pooled with 3 random donor BCs and one unit of PAS-E each to yield plasma-reduced platelet concentrates (PCs). Samples for bacterial colony counting were collected after WB storage and immediately after blood component production. Sterility testing in PCs (n = 12 for each species) was performed by bacterial culture after 7 days of storage.

Results

Bacterial growth in WB varied remarkably between donations and species. Streptococcus species produced the highest titers in WB, whereas Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas fluorescens did not multiply. Centrifugation resulted in preferential accumulation of bacteria in BCs, with titers of up to 3.5 × 103 CFU/mL in BCs and up to ≤0.9 × 103 CFU/mL in BC-derived PCs. Overall, 72/144 PCs (50%) tested positive for bacteria after storage. Sterility test results were species-dependent, ranging from 12 of 12 PCs tested positive for Streptococcus pyogenes to 1 of 12 PCs positive for Escherichia coli. Bacterial contamination of RBC and plasma units was much less common and was associated with higher initial bacterial counts in the parent WB units.

Conclusions

Bacterial growth in WB is species-dependent and varies greatly between donations. Preferential accumulation of bacteria in BCs during manufacturing is a critical determinant of the contamination risk of BC-derived pooled PCs.

Assessment of bacterial growth in leukoreduced cold-stored whole blood supports overnight hold at room temperature prior to filtration: A pilot study

BACKGROUND AND OBJECTIVES

Whole blood (WB) transfusion has regained attention to treat trauma patients. We reported no significant changes in in vitro quality through 21 days of cold storage for leukoreduced WB (LCWB) when time to filtration was extended from 8 to 24 h from collection. This study evaluated the impact of extended WB-hold at room temperature (RT) prior to leukoreduction on proliferation of transfusion-relevant bacteria.

MATERIALS AND METHODS

WB units were spiked with suspensions of Klebsiella pneumoniae, Streptococcus pyogenes, Staphylococcus aureus and Listeria monocytogenes prepared in saline solution (SS) or trypticase soy broth (TSB) to a concentration of ~0.2 CFU/ml (N = 6). Spiked units were held at RT for 18-24 h before leukoreduction and cold-stored for 21 days. Bacterial growth was determined on days 2, 7, 14 and 21. In vitro quality of WB inoculated with unspiked diluents was assessed.

RESULTS

K. pneumoniae and S. pyogenes proliferated in WB prior to leukoreduction reaching concentrations ≤10² CFU/ml. These bacteria, however, did not proliferate during the subsequent cold storage. S. aureus did not survive in WB while L. monocytogenes reached a concentration of ~10² CFU/ml by day 21. LCWB in vitro quality was not affected by SS or TSB.

CONCLUSION

Extended WB-hold prior to leukoreduction allowed proliferation of bacteria able to resist immune clearance, although they did not grow to clinically significant levels. While L. monocytogenes proliferated in LCWB, clinically relevant concentrations were not reached by day 21. These data suggest that transfusing LCWB may not pose a significant bacterial contamination safety risk to transfusion patients.

Staphylococcus epidermidis undergoes global changes in gene expression during biofilm maturation in platelet concentrates

BACKGROUND

Staphylococcus epidermidis forms surface-attached aggregates (biofilms) when grown in platelet concentrates (PCs). Comparative transcriptome analyses were undertaken to investigate differential gene expression of S. epidermidis biofilms grown in PCs.

STUDY DESIGN AND METHODS

Two S. epidermidis strains isolated from human skin (AZ22 and AZ39) and one strain isolated from contaminated PCs (ST02) were grown in glucose-supplemented Trypticase Soy Broth (TSBg) and PCs. RNA was extracted and sequenced using Illumina HiSeq. Differential expression analysis was done using DESeq, and significantly differentially expressed genes (DEGs) were selected. DEGs were subjected to Kyoto encyclopedia of genes and genomes and Gene Ontology analyses. Differential gene expression was validated with quantitative reverse transcription-PCR.

RESULTS

A total of 436, 442, and 384 genes were expressed in AZ22, AZ39, and ST02, respectively. DEG analysis showed that 170, 172, and 117 genes were upregulated in PCs in comparison to TSBg, whereas 120, 135, and 89 genes were downregulated (p < .05) in mature biofilms of AZ22, AZ39, and ST02, respectively. Twenty-seven DEGs were shared by all three strains. While 76 DEGs were shared by AZ22 and AZ39, only 34 and 21 DEGs were common between ST02, and AZ22 and AZ39, respectively. Significant transcriptional expression changes were observed in genes involved in platelet-bacteria interaction, biofilm formation, production of virulence factors, and resistance to antimicrobial peptides and antibiotics.

CONCLUSION

Differential gene expression in S. epidermidis is triggered by the stressful PC storage environment. Upregulation of virulence and antimicrobial resistance genes could have clinical implications for transfusion patients.

Bacterial inactivation of platelet concentrates with the THERAFLEX UV-Platelets pathogen inactivation system

BACKGROUND

The THERAFLEX UV-Platelets system (Maco Pharma) uses ultraviolet C (UVC) light for pathogen inactivation (PI) of platelet concentrates (PCs) without any additional photoactive compound. The aim of the study was to systematically investigate bacterial inactivation with this system under conditions of intended use.

STUDY DESIGN AND METHODS

The robustness of the system was evaluated by assessing its capacity to inactivate high concentrations of different bacterial species in accordance with World Health Organization guidelines. The optimal use of the PI system was explored in time-to-treatment experiments by testing its ability to sterilize PCs contaminated with low levels of bacteria on the day of manufacture (target concentration, 100 colony-forming units/unit). The bacteria panel used for spiking experiments in this study included the World Health Organization International Repository Platelet Transfusion Relevant Reference Strains (n = 14), commercially available strains (n = 13), and in-house clinical isolates (n = 2).

RESULTS

Mean log reduction factors after UVC treatment ranged from 3.1 to 7.5 and varied between different strains of the same species. All PCs (n = 12/species) spiked with up to 200 colony-forming units/bag remained sterile until the end of storage when UVC treated 6 hours after spiking. UVC treatment 8 hours after spiking resulted in single breakthrough contaminations with the fast-growing species Escherichia coli and Streptococcus pyogenes.

CONCLUSION

The UVC-based THERAFLEX UV-Platelets system efficiently inactivates transfusion-relevant bacterial species in PCs. The comprehensive data from this study may provide a valuable basis for the optimal use of this UVC-based PI system.

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.

Bacterial survival and distribution during buffy coat platelet production

BACKGROUND AND OBJECTIVES

At Canadian Blood Services, buffy coat (BC) platelet concentrates (BC-PCs) show a generally lower bacterial contamination rate than apheresis PCs. This study investigated whether the PC production method contributes to this observation.

MATERIALS AND METHODS

Whole blood (WB) inoculated with eight bacterial strains was processed using the BC method. Bacteria were enumerated throughout BC-PC production and subsequent PC storage. Endotoxin production and bacterial adhesion to PC bags were evaluated during PC storage. PC quality was monitored by CD62P expression (flow cytometry) and changes in dynamic light scattering (ThromboLUX^® ).

RESULTS

During overnight WB hold, Staphylococcus epidermidis titres remained unchanged, commercial Escherichia coli and Klebsiella pneumoniae were eliminated and the remaining organisms proliferated to high concentrations. Through BC-PC production, bacteria segregated preferentially towards the cellular fractions compared to plasma (P < 0·05). During PC storage, most bacteria adhered to the PC bags and Gram negatives produced clinically significant endotoxin levels. Changes in CD62P expression or ThromboLUX scoring did not consistently reflect bacterial contamination in BC-PCs.

CONCLUSION

WB hold during BC-PC production does not have a broad-spectrum bactericidal effect, and therefore, other factors contribute to low rates of contamination in BC-PCs.

Safety of platelet transfusion: past, present and future

Platelet components became routinely available to many institutions in the late 1960s and since then utilization has steadily increased. Platelets are produced by three principal methods and their manufacturing process is regulated by multiple agencies. As the field of platelet transfusion has evolved, a broad array of strategies to improve platelet safety has developed. This review will explore the evolution of modern platelet component therapy, highlight the various risks associated with platelet transfusion and describe risk reduction strategies that have been implemented to improve platelet transfusion safety. In closing, the reader will be briefly introduced to select investigational platelet and platelet-mimetic products that have the potential to enhance platelet transfusion safety in the near future.

Diagnostic methods for platelet bacteria screening: current status and developments

Bacterial contamination of blood components and the prevention of transfusion-associated bacterial infection still remains a major challenge in transfusion medicine. Over the past few decades, a significant reduction in the transmission of viral infections has been achieved due to the introduction of mandatory virus screening. Platelet concentrates (PCs) represent one of the highest risks for bacterial infection. This is due to the required storage conditions for PCs in gas-permeable containers at room temperature with constant agitation, which support bacterial proliferation from low contamination levels to high titers. In contrast to virus screening, since 1997 in Germany bacterial testing of PCs is only performed as a routine quality control or, since 2008, to prolong the shelf life to 5 days. In general, bacterial screening of PCs by cultivation methods is implemented by the various blood services. Although these culturing systems will remain the gold standard, the significance of rapid methods for screening for bacterial contamination has increased over the last few years. These new methods provide powerful tools for increasing the bacterial safety of blood components. This article summarizes the course of policies and provisions introduced to increase bacterial safety of blood components in Germany. Furthermore, we give an overview of the different diagnostic methods for bacterial screening of PCs and their current applicability in routine screening processes.

Effects of storage temperature on hematopoietic stability and microbial safety of BM aspirates

Bone marrow (BM) remains a common source for hematopoietic SCT. Due to the transcutaneous approach, contamination with skin bacteria is common. The delay between harvest and transfusion can be considerable, potentially allowing for bacterial proliferation. The optimal transportation temperature, specifically with respect to bacterial growth and consequences thereof for hematopoietic quality, remain undefined. For 72 h, 66 individual BM samples, non-spiked/spiked with different bacteria, stored at 20-24 °C room temperature (RT) or 3-5 °C (cold), were serially analyzed for hematopoietic quality and microbial burden. Under most conditions, hematopoietic quality of BM was equal or better at RT: Typical BM contaminants (P. acnes and S. epidermidis) and E. coli were killed or bacterial proliferation was arrested at RT; hematopoietic quality was not impacted by the contamination. However, several pathogenic bacteria not typically found in BM (S. aureus and K. pneumoniae) proliferated dramatically at RT and impaired hematopoietic quality. Bacterial proliferation was arrested in the cold. The overwhelming majority of BM samples, that is, those that are sterile or contaminated only with skin commensals, will benefit from transportation at RT. Those bacteria that proliferate and perturb hematopoietic quality are not typically found in BM. Our data support recommendations for RT transportation and storage of BM.

Impact of solvent/detergent treatment of plasma on transfusion-relevant bacteria

BACKGROUND

A solvent/detergent (S/D) treatment in a medical device has been developed for pathogen reduction of plasma for transfusion. Impact of S/D on bacterial growth and on the capacity of complement to kill bacteria has been investigated in this study.

STUDY DESIGN AND METHODS

A pool of apheresis plasma from four donors was spiked with eight transfusion-relevant bacteria. Plasma was treated with 1% tri(n-butyl) phosphate and 1% Triton X-45 at 31°C for 90 min and then extracted by oil at 31°C for 70 min. Decomplemented plasma and Phosphate Buffer Saline were used as controls. Bacterial count was determined in samples taken immediately after spiking, or after S/D and oil treatment. Similar experiments were conducted using three individual recovered plasma donations. Bacteria growth inhibition tests were performed using discs soaked with plasma samples whether containing the S/D agents or not.

RESULTS

The mean reduction factors of Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae due to complement during S/D treatment were >8·75, 4·71, and 4·18 log in pooled plasma and >7·42, 2·24 and >6·08 log in individual plasmas, respectively. Bacillus cereus and Bacillus subtilis were inactivated by S/D (>7·04 and 1·60 log in pooled, and >6·06 and 2·39 in individual plasmas, respectively). Staphylococcus aureus, Staphylococcus epidermidis and Enterobacter cloacae did not multiply during S/D treatment of plasma. Growth inhibition tests revealed an inhibition of three gram-negative bacteria by complement and all gram-positive by S/D.

CONCLUSION

The S/D treatment of plasma does not alter the bactericidal activity of complement, and inactivates some gram-positive bacteria.

Pathogenicity of Bacteria Contaminating Blood Products

SUMMARY: Bacterial contaminations of blood products often originate from the flora of the donor. Normally, components of the skin flora less frequently give rise to severe or complicated infections, although their participation in such conditions has been described. In contrast, bacteria that can cause infections in immunocompetent persons may give rise to life-threatening infections when present in blood products. The latter microorganisms are well-equipped with a variety of virulence factors that contribute to their pathogenicity.

Laboratory Evaluation of the Effectiveness of Pathogen Reduction Procedures for Bacteria

SUMMARY: Bacterial contamination remains a leading factor for transfusion-associated serious morbidity and mortality. Pathogen reduction procedures offer a pro-active approach to prevent bacterial contamination of cellular blood components and especially of platelet concentrates. In the past, the laboratory evaluation of the effectiveness of the pathogen reduction procedures to minimise the bacterial load of blood components has been primarily based on log reduction assays similar to the assessment of antiviral activities. Bacteria strains with the ability to multiply in the blood components are seeded in highest possible cell numbers, the pathogen reduction procedure is applied, and the post-treatment number of bacteria is measured. The effectiveness of the procedure is characterised by calculating the log reduction of the post- to pre-treatment bacteria titres. More recently, protocols have been developed for experiments starting with a low bacteria load and monitoring the sterility of the blood component during the entire storage period of the blood component. Results for 3 different pathogen reduction technologies in these experimental models are compared and critical determinants for the results are addressed. The heterogeneity of results observed for different strains suggests that the introduction of international transfusion-relevant bacterial reference strains may facilitate the validity of findings in pathogen reduction experiments.

Establishment of the first international repository for transfusion-relevant bacteria reference strains: ISBT working party transfusion-transmitted infectious diseases (WP-TTID), subgroup on bacteria

BACKGROUND

Bacterial contamination of platelet concentrates (PCs) still remains a significant problem in transfusion with potential important clinical consequences, including death. The International Society of Blood Transfusion Working Party on Transfusion-Transmitted Infectious Diseases, Subgroup on Bacteria, organised an international study on Transfusion-Relevant Bacteria References to be used as a tool for development, validation and comparison of both bacterial screening and pathogen reduction methods.

MATERIAL AND METHODS

Four Bacteria References (Staphylococcus epidermidis PEI-B-06, Streptococcus pyogenes PEI-B-20, Klebsiella pneumoniae PEI-B-08 and Escherichia coli PEI-B-19) were selected regarding their ability to proliferate to high counts in PCs and distributed anonymised to 14 laboratories in 10 countries for identification, enumeration and bacterial proliferation in PCs after low spiking (0·3 and 0·03 CFU/ml), to simulate contamination occurring during blood donation.

RESULTS

Bacteria References were correctly identified in 98% of all 52 identifications. S. pyogenes and E. coli grew in PCs in 11 out of 12 laboratories, and K. pneumoniae and S. epidermidis replicated in all participating laboratories. The results of bacterial counts were very consistent between laboratories: the 95% confidence intervals were for S. epidermidis: 1·19-1·32 × 10(7) CFU/ml, S. pyogenes: 0·58-0·69 × 10(7) CFU/ml, K. pneumoniae: 18·71-20·26 × 10(7) CFU/ml and E. coli: 1·78-2·10 × 10(7) CFU/ml.

CONCLUSION

The study was undertaken as a proof of principle with the aim to demonstrate (i) the quality, stability and suitability of the bacterial strains for low-titre spiking of blood components, (ii) the property of donor-independent proliferation in PCs, and (iii) their suitability for worldwide shipping of deep frozen, blinded pathogenic bacteria. These aims were successfully fulfilled. The WHO Expert Committee Biological Standardisation has approved the adoption of these four bacteria strains as the first Repository for Transfusion-Relevant Bacteria Reference Strains and, additionally, endorsed as a project the addition of six further bacteria strain preparations suitable for control of platelet contamination as the next step of enlargement of the repository.

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.

Noninvasive pH measurement to monitor changes during suboptimal storage of platelet concentrates

BACKGROUND

Noninvasive pH measurement of platelet concentrates (PCs) was evaluated as a tool for the quality control of PC storage by simulating worst-case conditions.

STUDY DESIGN AND METHODS

PCs from pooling four buffy coats in 70% PAS-3M were both stored in bags wrapped to impair gas permeability and agitated or not until Day 9 of storage. pH values measured both in samples (electrode, blood gas analyzer) and noninvasively by fluorimetry (BCSI pH1000, Blood Cell Storage, Inc.) were compared groupwise and to changes in platelet (PLT) size and biochemical variables.

RESULTS

The noninvasive pH measurements agreed well with the results from each of the two reference methods (R(2) >0.9) in a wide range of pH values between 6.4 and 7.5. Changes of the pH of PCs (n=64) by all interventions (agitation or resting plus occlusion by 0, 25, 50, or 100%; n=8/group) were subtle but already significant after 20 to 24 hours of treatment in comparison to the controls. A steady state after Day 6 and reductions up to a mean pH of approximately 6.5 were observed. The extent of manipulation determined both the absolute pH differences to the controls and the interindividual variation of pH changes. Termination of the agitation significantly enhanced pH reduction by surface blockade. Significant changes were also observed for the mean PLT volume, β-thromboglobulin, and soluble P-selectin.

CONCLUSION

Noninvasive pH measurement in PCs using this technique reliably detects pH changes of 0.1 or more. Storage of PLTs in buffered additive solution requires profound impairment of gas exchange to trigger a substantial decline in pH.

Blood still kills: six strategies to further reduce allogeneic blood transfusion-related mortality

After reviewing the relative frequency of the causes of allogeneic blood transfusion-related mortality in the United States today, we present 6 possible strategies for further reducing such transfusion-related mortality. These are (1) avoidance of unnecessary transfusions through the use of evidence-based transfusion guidelines, to reduce potentially fatal (infectious as well as noninfectious) transfusion complications; (2) reduction in the risk of transfusion-related acute lung injury in recipients of platelet transfusions through the use of single-donor platelets collected from male donors, or female donors without a history of pregnancy or who have been shown not to have white blood cell (WBC) antibodies; (3) prevention of hemolytic transfusion reactions through the augmentation of patient identification procedures by the addition of information technologies, as well as through the prevention of additional red blood cell alloantibody formation in patients who are likely to need multiple transfusions in the future; (4) avoidance of pooled blood products (such as pooled whole blood-derived platelets) to reduce the risk of transmission of emerging transfusion-transmitted infections (TTIs) and the residual risk from known TTIs (especially transfusion-associated sepsis [TAS]); (5) WBC reduction of cellular blood components administered in cardiac surgery to prevent the poorly understood increased mortality seen in cardiac surgery patients in association with the receipt of non-WBC-reduced (compared with WBC-reduced) transfusion; and (6) pathogen reduction of platelet and plasma components to prevent the transfusion transmission of most emerging, potentially fatal TTIs and the residual risk of known TTIs (especially TAS).

Screening platelet concentrates for bacterial contamination: low numbers of bacteria and slow growth in contaminated units mandate an alternative approach to product safety

BACKGROUND AND OBJECTIVES

We introduced 100% screening of platelets for bacterial contamination in 2005 to reduce the risk of clinical sepsis from platelet transfusion. We test all outdating units again at expiry to assess the sensitivity of the initial test.

MATERIALS AND METHODS

We test all platelet concentrates prior to release for clinical use using a large volume automated culture technique on the day after manufacture. All units that expire unused are retested. Platelets still in stock on day 4 of storage may have a repeat culture performed, and are returned to stock with two extra days of shelf life.

RESULTS

Of 43,230 platelet units screened, 35 (0.08%) were positive; of 8282 expired unused, 18 (0.22%) were positive; and of 3310 day-4 retests, four (0.12%) were positive. Overall sensitivity of the initial screening test was 29.2% (95% confidence interval 19.4 to 39.1%). Thirteen of the 35 positive screening tests would have been expected to grow in both aerobic and anaerobic bottles; eight grew in aerobic culture only and five grew in anaerobic culture only, indicating that the likely number of bacteria in the contaminated platelet units at the time of sampling was less than 60 colony-forming unit per platelet unit.

CONCLUSIONS

Screening platelet concentrates for bacterial contamination using the most sensitive method available has a sensitivity of less than 40% because of the low numbers of bacteria in the initial contamination. Effective resolution of this problem will require a pathogen-inactivation technique.

Propionibacterium acnes lacks the capability to proliferate in platelet concentrates

BACKGROUND AND OBJECTIVES

Propionibacterium acnes is considered to be one of the most frequent contaminants of platelet concentrates (PCs) when anaerobic culture-based detection methods are used. But Propionibacteria are often detected too late when blood products have already been transfused. Therefore, its transfusion relevance is still demanding clarification because studies of the outcome of patients transfused with P. acnes-contaminated PCs are still uncommon. In this study, we monitored clinical effects in patients after transfusion of PCs, which were detected too late in sterility testing. Furthermore, we assessed the bacterial proliferation of Propionibacterium species seeded into PCs to clarify their significance for platelet bacteria screening.

MATERIALS AND METHODS

In the look-back process, we followed the route of the putative contaminated PC units from storage to transfusion. In the in vitro study, PCs were inoculated with 1-100 colony-forming unit (CFU)/ml of clinical isolates of Propionibacteria (n = 10). Sampling was performed during 10-day aerobic storage at 22 degrees C. The presence of bacteria was assessed by plating culture and automated BacT/Alert culture system.

RESULTS

Propionibacterium acnes shows slow or no growth under PC storage conditions. Clinical signs of adverse events after transfusion of potentially contaminated PC units were not reported.

CONCLUSION

Propionibacteria do not proliferate under PC storage conditions and therefore may be missed or detected too late when blood products have already been transfused.

pH value promotes growth of Staphylococcus epidermidis in platelet concentrates

BACKGROUND

The platelet (PLT) storage lesion is characterized metabolically by a pH value associated with lactic acid generation. PLT storage conditions support the growth of Staphylococcus epidermidis, the most common organism implicated in bacterial contamination of PLT concentrates (PCs). Here, different factors that influence bacterial growth in PCs are discussed and the relation between pH values of PCs and citrate plasma (CP) is studied, with emphasis on bacterial proliferation.

STUDY DESIGN AND METHODS

The PLT lesion with regard to pH decrease and lactic acid production was monitored during storage and correlated to bacterial proliferation properties. A total of 115 coagulase-negative staphylococci, especially S. epidermidis isolates, were characterized for their proliferation in different blood components (CP, buffy coat-derived, and apheresis PCs). Furthermore, the influence of donor-specific, product-specific, species-specific, and strain-specific factors on bacterial proliferation was investigated.

RESULTS

PCs showed a lower pH value in comparison to plasma during storage. Bacterial proliferation in PCs and the failure to grow in CP were determined with all organisms tested. No correlation to donor-specific, species-specific, or strain-specific factors was observed. Lowering the pH of CP resulted in bacterial proliferation, whereas a pH increase in the PC unit inhibited the proliferation of S. epidermidis.

CONCLUSION

With emphasis on bacterial proliferation, the significant difference between PC and CP is the presence of metabolizing PLTs. The pH values of stored PLTs, but not those of stored plasma, support the growth of S. epidermidis.

The residual risk of sepsis: modeling the effect of concentration on bacterial detection in two-bottle culture systems and an estimation of false-negative culture rates

BACKGROUND

Septic reactions continue to be reported with culture-tested platelet (PLT) products, probably due to false-negative results associated with inadequate sampling of low-concentration bacteria. The mechanism of test failure was modeled and false-negative rates were estimated utilizing published data.

STUDY DESIGN AND METHODS

The effect of concentration on the probability of sampling one or more viable bacteria in an 8-mL sample of a 300-mL product was determined. The ratio of single- versus dual-bottle-positive tests in repeated cultures utilizing two-bottle systems was used to assess mean bacterial concentrations and to predict false-negative tests.

RESULTS

Published reports reveal a mean residual risk of sepsis of 2.3 per 10(5) products tested. Modeling the effect of concentration predicts that 50 and 95 percent of samples are detected at 0.09 and 0.36 CFU per mL for organisms that grow under both aerobic and anaerobic conditions, and suggest a 50 and 5 percent false-negative culture rate at these concentrations. Reanalysis of published studies documenting single-bottle growth of nonfastidious organisms indicate that low bacterial concentrations are frequently encountered and predict false-negative cultures in products contaminated with common bacteria at rates that varied from 4 to more than 75 percent. The model highlights the weakness of the AABB definition of false-positive culture results at low bacterial concentrations, especially for organisms that grow poorly in aerobic storage conditions.

CONCLUSION

Continuing reports of septic reactions after transfusion of culture-tested apheresis PLTs, and frequent single-bottle-positive results when testing with two-bottle systems, suggest appreciable levels of false-negative results with a commercially available bacterial detection system (BacT/ALERT, bioMéreiux) as implemented.

Real-Time Polymerase Chain Reaction in Transfusion Medicine: Applications for Detection of Bacterial Contamination in Blood Products

Bacterial contamination of blood components, particularly of platelet concentrates (PCs), represents the greatest infectious risk in blood transfusion. Although the incidence of platelet bacterial contamination is approximately 1 per 2,000 U, the urgent need for a method for the routine screening of PCs to improve safety for patients had not been considered for a long time. Besides the culturing systems, which will remain the criterion standard, rapid methods for sterility screening will play a more important role in transfusion medicine in the future. In particular, nucleic acid amplification techniques (NATs) are powerful potential tools for bacterial screening assays. The combination of excellent sensitivity and specificity, reduced contamination risk, ease of performance, and speed has made real-time polymerase chain reaction (PCR) technology an appealing alternative to conventional culture-based testing methods. When using real-time PCR for the detection of bacterial contamination, several points have to be considered. The main focus is the choice of the target gene; the assay format; the nucleic acid extraction method, depending on the sample type; and the evaluation of an ideal sampling strategy. However, several factors such as the availability of bacterial-derived nucleic acid amplification reagents, the impracticability, and the cost have limited the use of NATs until now. Attempts to reduce the presence of contaminating nucleic acids from reagents in real-time PCR have been described, but none of these approaches have proven to be very effective or to lower the sensitivity of the assay. Recently, a number of broad-range NAT assays targeting the 16S ribosomal DNA or 23S ribosomal RNA for the detection of bacteria based on real-time technology have been reported. This review will give a short survey of current approaches to and the limitations of the application of real-time PCR for bacterial detection in blood components, with emphasis on the bacterial contamination of PCs.

Detection of bacteria in platelet concentrates prepared from spiked single donations using cultural and molecular genetic methods

Bacteria show differences in their growth kinetics depending on the type of blood component. On to storage at 22 degrees C, platelet concentrates (PCs) seem to be more prone to bacterial multiplication than red cell concentrates. Knowledge of the potential for bacterial proliferation in blood components, which are stored at a range of temperatures, is essential before considering implementation of a detection strategy. The efficacy of bacterial detection was determined, using real-time reverse transcriptase-polymerase chain reaction (RT-PCR), following bacterial growth in blood components obtained from a deliberately contaminated whole-blood (WB) unit. Cultivation was used as the reference method. WB was spiked with 2 colony-forming units mL(-1)Staphylococcus epidermidis or Klebsiella pneumoniae, kept for 15 h at room temperature and component preparation was processed. Samples were drawn, at intervals throughout the whole separation process, from each blood component. Nucleic acids were extracted using an automated high-volume extraction method. The 15-h storage revealed an insignificant increase in bacterial titre. No bacterial growth was detected in red blood cell or plasma units. K. pneumoniae showed rapid growth in the pooled PC and could be detected immediately after preparation using RT-PCR. S. epidermidis grew slowly and was detected 24 h after separation. These experiments show that sampling is indicative at 24 h after preparation of PCs at the earliest to minimize the sampling error.