Evaluation of the enhanced bacterial detection system for screening of contaminated platelets

Bacterial culture time to detection in platelet components: An evidence synthesis and estimation of detection failures

BACKGROUND

Non-pathogen reduction platelet bacterial risk control strategies in the US FDA guidance include at least one culture. Almost all of these strategies have a culture hold time of ≥12 h. Studies have reported time to detection (TTD) of bacterial cultures inoculated with bacteria from contaminated platelets, but these data and estimates of risk associated with detection failures have not been synthesized.

METHODS

We performed a literature search to identify studies reporting TTD for samples obtained from spiked platelet components. Using extracted data, regression analysis was used to estimate TTD for culture bottles at different inoculum sizes. Detection failures were defined as events in which contaminated components are transfused to a patient. We then used published data on time of transfusion (ToT) to estimate the risk of detection failures in practice.

RESULTS

The search identified 1427 studies, of which 16 were included for analysis. TTD data were available for 16 different organisms, including 14 in aerobic cultures and 11 in anaerobic cultures. For inocula of 1 colony forming unit (CFU), the average TTD for aerobic organisms was 19.2 h while it was 24.9 h in anaerobic organisms, but there was substantial overall variation. A hold time of 12 versus 24 h had minimal effect for most organisms.

CONCLUSION

TTD variation occurs between bacterial species and within a particular species. Under typical inventory management, the relative contribution of culture detection failures is much smaller than the residual risk from sampling failures. Increasing the hold period beyond 12 h has limited value.

Aptamer-based diagnostic and therapeutic approaches in animals: Current potential and challenges

Fast and precise diagnosis of infectious and non-infectious animal diseases and their targeted treatments are of utmost importance for their clinical management. The existing biochemical, serological and molecular methods of disease diagnosis need improvement in their specificity, sensitivity and cost and, are generally not amenable for being used as points-of-care (POC) device. Further, with dramatic changes in environment and farm management practices, one should also arm ourselves and prepare for emerging and re-emerging animal diseases such as cancer, prion diseases, COVID-19, influenza etc. Aptamer – oligonucleotide or short peptides that can specifically bind to target molecules – have increasingly become popular in developing biosensors for sensitive detection of analytes, pathogens (bacteria, virus, fungus, prions), drug residues, toxins and, cancerous cells. They have also been proven successful in the cellular delivery of drugs and targeted therapy of infectious diseases and physiological disorders. However, the in vivo application of aptamer-mediated biosensing and therapy in animals has been limited. This paper reviews the existing reports on the application of aptamer-based biosensors and targeted therapy in animals. It also dissects the various modifications to aptamers that were found to be successful in in vivo application of the aptamers in diagnostics and therapeutics. Finally, it also highlights major challenges and future directions in the application of aptamers in the field of veterinary medicine.

Advanced biosensors for detection of pathogens related to livestock and poultry

Infectious animal diseases caused by pathogenic microorganisms such as bacteria and viruses threaten the health and well-being of wildlife, livestock, and human populations, limit productivity and increase significantly economic losses to each sector. The pathogen detection is an important step for the diagnostics, successful treatment of animal infection diseases and control management in farms and field conditions. Current techniques employed to diagnose pathogens in livestock and poultry include classical plate-based methods and conventional biochemical methods as enzyme-linked immunosorbent assays (ELISA). These methods are time-consuming and frequently incapable to distinguish between low and highly pathogenic strains. Molecular techniques such as polymerase chain reaction (PCR) and real time PCR (RT-PCR) have also been proposed to be used to diagnose and identify relevant infectious disease in animals. However these DNA-based methodologies need isolated genetic materials and sophisticated instruments, being not suitable for in field analysis. Consequently, there is strong interest for developing new swift point-of-care biosensing systems for early detection of animal diseases with high sensitivity and specificity. In this review, we provide an overview of the innovative biosensing systems that can be applied for livestock pathogen detection. Different sensing strategies based on DNA receptors, glycan, aptamers and antibodies are presented. Besides devices still at development level some are validated according to standards of the World Organization for Animal Health and are commercially available. Especially, paper-based platforms proposed as an affordable, rapid and easy to perform sensing systems for implementation in field condition are included in this review.

Selective capture and rapid identification of E. coli O157:H7 by carbon nanotube multilayer biosensors and microfluidic chip-based LAMP

A combination of CNT multilayer biosensors and microfluidic chip-based LAMP was developed for the capture and visual detection of E. coli O157:H7.

Noninvasive pH monitoring for bacterial detection in platelet concentrates

BACKGROUND

Bacterial contamination of platelet concentrates (PCs) remains the prevalent posttransfusion infectious risk. The pH SAFE system, a noninvasive method used to measure pH of PC for quality control, was evaluated herein as a rapid method to detect bacterial contamination in PCs.

STUDY DESIGN AND METHODS

Pairs of ABO-D-matched apheresis and buffy coat PCs were pooled and split into two pH SAFE platelet bags. One of the bags served as the control unit, while the other was inoculated with one of nine clinically relevant bacteria (target concentration approx. 1 colony-forming units [CFUs]/mL). The pH of both PCs was measured over 7 days of storage at approximately 4-hour intervals during daytime. One-milliliter samples were taken at the testing points to determine bacterial concentration.

RESULTS

PCs with pH values of less than 6.6 or with a pH change over time (ΔpH/Δtime) greater or equal than 0.046 pH units/hr are suspected of being contaminated. pH decreased significantly during storage in all bacterially inoculated PC at concentrations of more than 10(7) CFUs/mL (p < 0.0001). A significant decrease in pH (p < 0.0001) was noticed as early as 28 hours in units with Bacillus cereus and as late as 125 hours in units containing Staphylococcus epidermidis. Interestingly, PCs containing Gram-negative species showed a decline in pH followed by a rebound.

CONCLUSIONS

The pH SAFE system allows for repeated, noninvasive pH screening during PC storage. A significant decrease in pH could serve as an indicator of clinically significant levels of bacterial contamination. Since differences in pH decline were observed among bacterial species, continuous pH monitoring in PCs is recommended.

[Prevention of bacterial risk: pathogen inactivation/detection of bacteria]

Bacterial contamination of blood products remains the most important infectious risk of blood transfusion in 2013. Platelet concentrates (PC) are in cause in the majority of the transfusion reaction due to bacterial contaminations. A lot of prevention methods have been developed over the last 10 years (pre-donation interview, skin decontamination, diversion of the first 30 mL of the donation, leuko-reduction...), they have focused on limiting the contamination of the donations and prevent the bacterial growth in donations and/or in the blood products. These measures were effective and led to significantly reducing the risk of adverse effects associated with bacterial growth. However, every year there are about six accidents (with a high level of imputability) and one death. The reduction of the bacterial risk remains a priority for the French Blood Establishment (EFS). The procedure for skin disinfection is going to be improved in order to further strengthen this crucial step to avoid the contamination of donation. Methods of pathogen inactivation applied to plasma and PC are available in France and their effectiveness is demonstrated on the bacterial risk. Methods for bacterial detection of PC are used in many countries now. Automated culture is the most common. Alternatives are now available in the form of rapid tests able to analyze the PC just before the delivery and avoid false negatives observed with automated culture. Assessments are under way to confirm these benefits in 2013.

Extension of platelet shelf life from 4 to 5 days by implementation of a new screening strategy in Germany

BACKGROUND

The Paul-Ehrlich-Institute analysed all fatalities due to bacterial infections between 1997 and 2007. Thereafter, the platelet shelf life was reduced to a maximum of 4 days after blood donation because the majority of all cases of severe transfusion-transmitted bacterial infections occurred with day 5 platelets. The current study compares the analytical sensitivity and the diagnostic specificity of four rapid bacterial detection procedures.

METHODS

Nine transfusion-relevant bacterial strains were spiked in pooled platelets or apheresis platelets at a low concentration (10 CFU/bag). Samples were collected after day 3, day 4 and day 5 and investigated by four rapid bacterial detection methods (modified BacT/ALERT, Bactiflow, FACS method and 16s DNA PCR methods).

RESULTS

Seven out of nine bacterial strains were adequately detected by BacT/ALERT, Bactiflow and PCR in apheresis platelets and pooled platelets after sample collection at day 3, day 4 and day 5. For three bacterial strains, analytical sensitivity was reduced for the FACS method. Two bacterial strains did not grow under the storage conditions in either pooled or apheresis platelets.

CONCLUSIONS

A late sample collection on day 3, day 4 or day 5 after blood donation in combination with a rapid bacterial detection method offers a new opportunity to improve blood safety and reduce errors due to sampling., BacT/ALERT, Bactiflow or 16s ID-NAT are feasible for late bacterial screening in platelets may provide data which support the extension of platelet shelf life in Germany to 5 days.

Screening of platelets for bacterial contamination at the Welsh Blood Service

BACKGROUND AND OBJECTIVE

This report details the results of the implementation of a bacterial screening system at the Welsh Blood Service and provides an estimate of the levels of bacterial contamination at the time of sampling.

MATERIALS AND METHODS

Apheresis (Caridian BCT) and buffy coat-derived pooled platelet components were sampled on day 1 for bacterial contamination and the sample was monitored throughout the lifespan of the platelet component. Unused platelet components were re-tested to determine the effectiveness of the screening. Results from the BacT/ALERT are uploaded to the in-house Blood Establishment Computer System (BECS) every 12 min. Positive alerts are automatically sent to staff, facilitating a timely intervention.

RESULTS

Between February 2003 and March 2010 the screening system tested 54 828 platelets and detected 257 (1 in 213) initial positives of which 35 (1 in 1567, 0·06%) were confirmed [95% confidence interval (CI), 0·04-0·08%]. Additionally, screening of 6438 unused platelet components detected another 6 (1 in 1073, 0·09%) confirmed positives not detected during initial testing (95% CI, 0·02-0·16%). Analysis of the data suggests that on day 1 the number of bacteria in such platelet component packs was between 5 and 62 cfus total. Day 1 culture has a sensitivity of 40%.

CONCLUSIONS

The bacterial screening system has removed a significant number, but not all bacterially contaminated platelet components from the supply. The sample volume is an important factor in sensitivity due to the low number of bacteria in a platelet component pack on day 1. An effective notification and recall system is a critical part of the bacterial screening system.

Use of the RQI test for bacterial screening of whole blood platelets

We compare our experience using a new rapid qualitative immunoassay (RQI) test (platelet Pan Genera Detection, Verax, Worcester, MA) for bacterial screening of whole blood platelet (WBP) pools with our previous WBP bacterial screen, pH testing. All WBP pools were RQI tested at the time of issue. All RQI+ pools were cultured in an automated culture system, with subsequent bacterial identification if the culture was positive. During approximately 5.5 months, 7,733 WBP pools were RQI tested. There were 14 positive RQI tests; 12 WBP pools were sterile when cultured and considered false-positive RQI tests. One pool was positive for coagulase-negative Staphylococcus, while another was positive for group B Streptococcus. The specificity and positive predictive value of the RQI test were 99.85% and 14.3%, respectively. The specificity and positive predictive value of the RQI test were higher than pH testing, leading to less waste of sterile WBP pools.

A noninvasive near infrared system for detection of platelet components contaminated with bacteria

BACKGROUND

Platelet (PLT) transfusion-associated bacterial sepsis has remained a substantial patient risk, primarily due to lacking effective and point-of-issue measures to detect bacterial contamination. This study describes near infrared (NIR) spectroscopy to examine inoculated PLTs without sampling within a few seconds.

STUDY DESIGN AND METHODS

This study evaluated apheresis PLTs inoculated with low concentrations of Bacillus cereus and Staphylococcus epidermidis, comparing with sterile bags. Short-wavelength NIR spectra over the range from 700 to 1100 nm in the transmittance mode were obtained using research (NIRS6500, Foss NIRSystems) and portable (NIRGun, Shizuoka Shibuya Seiki) instruments at 6-hour intervals from 0 to 72 hours after inoculation (HAI).

RESULTS

The sensitivity of the NIRS6500 was 100% (43/43) and 98% (50/51) after incubating PLTs inoculated with B. cereus for 42 HAI or more and with S. epidermidis for 54 HAI or more, respectively. Difference spectra calculated by subtracting the NIR spectra of stored PLTs with that of the same PLTs measured at 0 HAI improved the discrimination results compared with conventional second derivative spectra.

CONCLUSION

The NIRS6500 system can provide a PLT monitoring system based on difference spectra. The chemical components of PLTs that were influenced by bacterial metabolism seemed to play an important role in the calibration structure. Further studies should examine samples spiked with various species of prevalent bacteria.

Analysis of bacterial detection in whole blood-derived platelets by quantitative glucose testing at a university medical center

After the March 2004 implementation of American Association of Blood Banks standards regarding platelet bacterial detection, we began quantitative glucose screening of whole blood-derived platelets (WB-P). The glucose level was measured immediately before component release--often storage day 4 or 5--using the Glucometer SureStep Flexx Meter (LifeScan, Milpitas, CA), with a positive cutoff of less than 500 mg/dL; failing units were cultured and not transfused. During 29 months (March 1, 2004-July 31, 2006) 93,073 units of WB-P were tested. Initially, 929 units (0.998%) screened positively. Bacterial growth was culture-confirmed in 6 units, for a bacterial contamination incidence of 0.006% and a true-positive rate of 6.4/100,000. Three additional culture-confirmed contamination cases were detected in transfused units causing febrile nonhemolytic reactions, for a false-negative rate of 3.2/100,000. Our overall contamination prevalence was 9.6/100,000 units of platelets transfused, lower than ordinarily cited, and showed a false-negative rate remarkably congruent to that of culture: 3.2/100,000. A low-sensitivity screening test applied late in platelet shelf-life can be comparable to culture in preventing bacterial-related morbidity.

Methods for the detection of bacterial contamination in blood products

Culture-based and molecular assays have been developed for the screening of platelet concentrates and other blood components for bacterial contaminations. In this review, the principles of the assays are outlined. The focus of this review is the assessment of the analytical qualities of the methods. Spiking studies by adding defined levels of a wide range of bacteria to the complex biological matrix provide the first basis to evaluate and compare the qualities of methods for bacterial detection. The sensitivity acceptable for reliable screening for bacteria critically depends on the timing of either early sampling (within a period of up to 24 h after preparation of the blood component) or late sampling (a few hours before issuing the blood component). Large screening studies are essential to confirm both adequate sensitivity and specificity of the testing. In the ideal setting, these studies are prospectively planned and include systematic surveillance of adverse events in response to the administration of the screened products. The findings from sterility testing (predominantly with automated systems for detection of bacteria based on CO(2) generation) of more than 550,000 platelet concentrates in 13 studies are summarised. The limitations of the early sampling and the "negative-to-date" strategy to issue platelet concentrates are addressed. A few reported cases of probable transmission of bacteria by platelet transfusion despite negative screening tests emphasise the need to further develop optimised methods for testing of bacteria blood components.

Strategies of bacteria screening in cellular blood components

Since the impressive reduction of transfusion-transmitted virus infections, bacterial infections by blood transfusion represent the most important infection risk. Platelet concentrates are the current focus of attention, as they are stored under temperature conditions which allow growth of contaminating bacteria up to 10(10) and more microbes per platelet bag. This paper does not consider the pathogen reduction methods but will assess suitable screening methods. Beside conventional microbiological approaches or surrogate markers, several efficient methods able to detect bacterial contamination in platelets are available on the market. They need to be divided into two different methodological principles: the cultivation methods and rapid methods. Cultivation or incubation methods require some time for signal production as they depend on growth of microbes. Thus, they have to be combined with early sampling, i.e., the sample to be examined has to be drawn from the blood component 1 day after donation. Their advantage is the relatively uncomplicated implementation into the logistics of blood banks. Because of the initially very low count of bacteria after donation, a certain small sampling error in application of that strategy remains. Rapid methods are able to produce the diagnosis within a short time. Therefore, they allow postponing of sample drawing, ideally up to the time immediately before transfusion. However, this procedure causes logistic complications. On the other hand, late sampling combined with a rapid method will prevent the transfusion of highly contaminated platelet concentrates leading to acute septic shock up to the death of the patient. Considering the sum of different aspects including the supply of patients, the potential improvement of microbial safety of platelet concentrates is comparable in both strategies.

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.

High-volume extraction of nucleic acids by magnetic bead technology for ultrasensitive detection of bacteria in blood components

BACKGROUND

Nucleic acid isolation, the most technically demanding and laborious procedure performed in molecular diagnostics, harbors the potential for improvements in automation. A recent development is the use of magnetic beads covered with nucleic acid-binding matrices. We adapted this technology with a broad-range 23S rRNA real-time reverse transcription (RT)-PCR assay for fast and sensitive detection of bacterial contamination of blood products.

METHODS

We investigated different protocols for an automated high-volume extraction method based on magnetic-separation technology for the extraction of bacterial nucleic acids from platelet concentrates (PCs). We added 2 model bacteria, Staphylococcus epidermidis and Escherichia coli, to a single pool of apheresis-derived, single-donor platelets and assayed the PCs by real-time RT-PCR analysis with an improved primer-probe system and locked nucleic acid technology. Co-amplification of human beta(2)-microglobulin mRNA served as an internal control (IC). We used probit analysis to calculate the minimum concentration of bacteria that would be detected with 95% confidence.

RESULTS

For automated magnetic bead-based extraction technology with the real-time RT-PCR, the 95% detection limit was 29 x 10(3) colony-forming units (CFU)/L for S. epidermidis and 22 x 10(3) CFU/L for E. coli. No false-positive results occurred, either due to nucleic acid contamination of reagents or externally during testing of 1030 PCs.

CONCLUSIONS

High-volume nucleic acid extraction improved the detection limit of the assay. The improvement of the primer-probe system and the integration of an IC make the RT-PCR assay appropriate for bacteria screening of platelets.

Proteomics and transfusion medicine: Future perspectives

Limited number of important discoveries have greatly contributed to the progresses achieved in the blood transfusion; ABO histo-blood groups, citrate as anticoagulant, fractionation of plasma proteins, plastic bags and apheresis machines. Three major types of blood products are transfused to patients: red cell concentrates, platelet concentrates and fresh frozen plasma. Several parameters of these products change during storage process and they have been well studied over the years. However, several aspects have completely been ignored; in particular those related to peptide and protein changes. This review presents what has been done using proteomic tools and the potentials of proteomics for transfusion medicine.