Methods for the detection of bacterial contamination in blood products

Molecular detection of bacterial contamination in plasma using magnetic-based enrichment

Bacterial contamination of blood products is a major problem in transfusion medicine, in terms of both morbidity and mortality. Platelets (PLTs) are stored at room temperature (under constant agitation) for more than 5 days, and bacteria can thus grow significantly from a low level to high titers. However, conventional methods like blood culture and lateral flow assay have disadvantages such as long detection time, low sensitivity, and the need for a large volume of blood components. We used real-time polymerase chain reaction (PCR) assays with antibiotic-conjugated magnetic nanobeads (MNBs) to detect enriched Gram-positive and -negative bacteria. The MNBs were coated with polyethylene glycol (PEG) to prevent aggregation by blood components. Over 80% of all bacteria were captured by the MNBs, and the levels of detection were 10¹ colony forming unit [CFU]/mL and 10² CFU/mL for Gram-positive and -negative bacteria, respectively. The detection time is < 3 h using only small volumes of blood components. Thus, compared to conventional methods, real-time PCR using MNBs allows for rapid detection with high sensitivity using only a small volume of blood components.

Multimodal Magneto-Fluorescent Nanosensor for Rapid and Specific Detection of Blood-Borne Pathogens

Detection of bacterial contaminants in blood and platelet concentrates (PCs) continues to be challenging in clinical settings despite available current testing methods. At the same time, it is important to detect the low bacterial contaminants present at the time of transfusion. Herein, we report the design and synthesis of a dual-modal magneto-fluorescent nanosensor (MFnS) by integrating magnetic relaxation and fluorescence modalities for the wide-range detection of blood-borne pathogens. In this study, functional MFnS are designed to specifically detect Staphylococcus epidermidis and Escherichia coli, two of the predominant bacterial contaminants of PCs. Specific interaction between the target pathogen and functional MFnS resulted in the change of water proton's magnetic relaxation time (T2 MR), indicative of sensitive detection of the target bacteria from low to high colony forming unit (CFU). In addition, the acquired MR signal of MFnS further facilitated the quantitative assessment of the slow and fast growth kinetics of target pathogens. Moreover, the presence of fluorescence modality in MFnS allowed for the detection of multi-contaminants. The bacterial detection was also performed in complex media including whole blood and platelet concentrates, which further demonstrated for it's robust detection sensitivity. Overall, our study indicated that the designer MFnS will have potential for the wide-range detection of blood-borne pathogens, and features desirable qualities including timeliness, sensitivity and, specificity.

Combining culture and microbead-based immunoassay for the early and generic detection of bacteria in platelet concentrates

BACKGROUND

Despite current preventive strategies, bacterial contamination of platelets is the highest residual infectious risk in transfusion. Bacteria can grow from an initial concentration of 0.03-0.3 colony-forming units (CFUs)/mL up to 10⁸ to 10⁹ CFUs/mL over the product shelf life. The aim of this study was to develop a cost-effective approach for an early, rapid, sensitive, and generic detection of bacteria in platelet concentrates.

STUDY DESIGN AND METHODS

A large panel of bacteria involved in transfusion reactions, including clinical isolates and reference strains, was established. Sampling was performed 24 hours after platelet spiking. After an optimized culture step for increasing bacterial growth, a microbead-based immunoassay allowed the generic detection of bacteria. Antibody production and immunoassay development took place exclusively with bacteria spiked in fresh platelet concentrates to improve the specificity of the test.

RESULTS

Antibodies for the generic detection of either gram-negative or gram-positive bacteria were selected for the microbead-based immunoassay. Our approach, combining the improved culture step with the immunoassay, allowed sensitive detection of 1 to 10 CFUs/mL for gram-negative and 1 to 10² CFUs/mL for gram-positive species.

CONCLUSION

In this study, a new approach combining bacterial culture with immunoassay was developed for the generic and sensitive detection of bacteria in platelet concentrates. This efficient and easily automatable approach allows tested platelets to be used on Day 2 after collection and could represent an alternative strategy for reducing the risk of transfusion-transmitted bacterial infections. This strategy could be adapted for the detection of bacteria in other cellular products.

Rapid identification of microorganisms from platelet concentrates by matrix-assisted laser desorption ionization time-of-flight mass spectrometry after short-term incubation on liquid medium

BACKGROUND

Platelets (PLTs) are especially affected by the risk of bacterial contamination. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) is an accurate method for the routine identification of bacterial isolates in microbiology laboratories. We directly applied the MALDI-TOF method to bacterial detection in PLTs. In this study, we evaluated the sensitivity, specificity, and speed of a direct MALDI-TOF approach compared to the conventional method BACTEC.

STUDY DESIGN AND METHODS

Eight bacteria associated with PLT contamination, cited by the ISBT on transfusion-transmitted infectious diseases, were spiked into PLTs for a final concentration of approximately 100 CFU/bag (n = 5 for each strain). The PLTs were then agitated for 24 hours. One milliliter of PLTs was incubated in a shaker incubator for 8 hours at 37°C with 1 mL of trypticase soy broth (TSB). The spectra were analyzed using the MALDI Biotyper software. As a control, 8 mL of PLTs incubated into BACTEC bottles and a positive bottle were subcultured to ensure identification of bacterial growth.

RESULTS

Regardless of the strain of PLTs tested, MALDI-TOF analysis made detection and early identification possible at 8 hours. Analysis by BACTEC of PLTs infected with Escherichia coli, Bacillus cereus, and Providencia stuartii made early identification possible. For the remaining bacteria, the detection time by BACTEC was significantly longer than 8 hours.

CONCLUSION

We demonstrated the possibility of detecting bacteria in PLTs using a standardized culture step in TSB with MALDI-TOF, regardless of the strain, with the same specificity and analytical sensitivity and with a time to results of 12 hours. This direct method presented rapid and reliable results.

Bacterial screening of platelet concentrates on day 2 and 3 with flow cytometry: the optimal sampling time point?

BACKGROUND

There is growing concern on the residual risk of bacterial contamination of platelet concentrates in Germany, despite the reduction of the shelf-life of these concentrates and the introduction of bacterial screening. In this study, the applicability of the BactiFlow flow cytometric assay for bacterial screening of platelet concentrates on day 2 or 3 of their shelf-life was assessed in two German blood services. The results were used to evaluate currently implemented or newly discussed screening strategies.

MATERIALS AND METHODS

Two thousand and ten apheresis platelet concentrates were tested on day 2 or day 3 after donation using BactiFlow flow cytometry. Reactive samples were confirmed by the BacT/Alert culture system.

RESULTS

Twenty-four of the 2,100 platelet concentrates tested were reactive in the first test by BactiFlow. Of these 24 platelet concentrates, 12 were false-positive and the other 12 were initially reactive. None of the microbiological cultures of the initially reactive samples was positive. Parallel examination of 1,026 platelet concentrates by culture revealed three positive platelet concentrates with bacteria detected only in the anaerobic culture bottle and identified as Staphylococcus species. Two platelet concentrates were confirmed positive for Staphylcoccus epidermidis by culture. Retrospective analysis of the growth kinetics of the bacteria indicated that the bacterial titres were most likely below the diagnostic sensitivity of the BactiFlow assay (<300 CFU/mL) and probably had no transfusion relevance.

CONCLUSIONS

The BactiFlow assay is very convenient for bacterial screening of platelet concentrates independently of the testing day and the screening strategy. Although the optimal screening strategy could not be defined, this study provides further data to help achieve this goal.

Three different bacterial detection systems for platelet concentrates under inter-laboratory conditions

BACKGROUND

A variety of screening methods are currently used worldwide in order to decrease the risk of transfusion-transmitted sepsis and improve the safety of PCs.

METHODS/MATERIALS

PCs inoculated with five different transfusion-relevant species of bacteria at concentrations of 1, 10, and 100 colony-forming units (CFU)ml(-1) were stored at 22°C for 7 days. Flow cytometry (FACS), BacT/Alert automated culturing, and a quantitative real-time PCR (Q-PCR) were then used to detect the presence of bacteria in samples prepared from these PCs.

RESULTS

At the initial spiking concentrations of 1, 10, and 100 CFU ml(-1), Q-PCR detected all five bacterial species tested. Screening with the BacT/Alert culture-based system allowed bacterial detection (inoculated on day 0) within a mean time of 15.13 h for all three spiking concentrations. Using FACS, positive signals were obtained for all three concentrations of Escherichia coli and Bacillus cereus on day 1 and for initial spiking concentrations of Pseudomonas aeruginosa and Staphylococcus aureus of 1 CFU ml(-1) on day 2. For Staphylococcus epidermidis, detection of an initial inoculum of 1 CFU ml(-1) was possible only beginning on day 6.

CONCLUSION

This study shows that under standard laboratory conditions the sensitivity of FACS in the detection of bacterial contamination of PCs was lower than that of either the BacT/Alert automated culturing method or Q-PCR.

Oxygen measurements in platelet fluids - a new non-invasive method to detect bacterial contaminations in platelets

BACKGROUND

The residual risk for bacterial contamination in blood components especially in platelets is one to two orders of magnitude higher than for transfusion relevant viral infections. The majority of all bacterial transmitted fatalities occurred at the end of platelet shelf life. Therefore, the maximum shelf life of platelet concentrates (PC) was reduced to 4 days after blood donation in Germany in 2008.

METHODS

A new continuous non-invasive bacterial detection method was developed by O(2) measurements in the platelet fluids and tested with 10 transfusion relevant bacteria species.

RESULTS

The bacterial concentration at the time point of a positive signal of PreSense O(2) ranged between 10(2) and 10(5) CFU mL(-1) . Harmful transfusion-transmitted bacterial infection would have probably been prevented by this novel technology. Only strict anaerobic bacteria strains like Clostridium perfringens were not detected within the study period of 72 h.

CONCLUSIONS

The described non-invasive bacterial detection method represents a new approach to prevent transmission of bacterial infection in platelets. The method is characterised by the advantage that all investigations can be performed until right up to the time of transfusion, and therefore, reduce the risk for sample errors to a minimum.

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.

Implementation of Bacterial Detection Methods into Blood Donor Screening - Overview of Different Technologies

SUMMARY: BACKGROUND: Through the implementation of modern technology, such as nucleic acid testing, over the last two decades, blood safety has improved considerably in that the risk of viral infection is less than 1 in a million blood transfusions. By contrast, the residual risk of transfusion-associated bacterial infection is stable at approximately 1 in 2,000 to 1 in 3,000 in platelets. To improve blood safety with regard to bacterial infections, many countries have implemented bacterial screening methods as part of their blood donor screening programmes. METHODS: BACTERIAL DETECTION METHODS ARE CLUSTERED INTO THREE GROUPS: i) culture methods in combination with the 'negative-to-date' concept, ii) rapid detection systems with a late sample collection, and iii) bedside screening tests. RESULTS: The culture methods are convincing because of their very high analytical sensitivity. Nevertheless, false-negative culture results and subsequent fatalities were reported in several countries. Rapid bacterial systems are characterised as having short testing time but reduced sensitivity. Sample errors are prevented by late sample collection. Finally, bedside tests reduce the risk for sample errors to a minimum, but testing outside of blood donation services may have risks for general testing failures. CONCLUSION: Bacterial screening of blood products, especially platelets, can be performed using a broad range of technologies. Each system exhibits advantages and disadvantages and offers only a temporary solution until a general pathogen inactivation technology is available for all blood components.

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.

[Techniques of preparation and indications of labile blood products]

Labile blood products are obtained from samples of whole blood or aphaeresis. The techniques of preparation evolve with technological advances, which allow both an increasing automation and an intensification of the sanitary safety of the blood products. Over the last ten years, thanks to the availability of new technologies, several measures have been introduced in order to reduce the risk of transmission of pathogens and prevent the onset of transfusion-related acute lung injury (TRALI): leukoreduction, use of platelet storage solutions, inactivation of plasma and presumably of platelets in a very near future. The control of transfusion risk also depends on proper use of labile blood products. To assist the prescriber in his treatment options and to standardize practices, the French Agency for Sanitary Safety of Health Products has issued recommendations in terms of utilization of blood products that are detailed in this review of major labile blood products available.

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.

[Problems in microbial safety of advanced therapy medicinal products. Squaring the circle]

Today, sterility of parenteral drugs is practically guaranteed. Well-defined procedures in the pharmaceutical industry enable effective protection against contamination by bacteria and fungi. In contrast, problems regarding microbial safety of advanced therapy medicinal products (ATMPs), especially of cell therapeutics, are at best only partially solved. The latter should be understood as a challenge for manufacturers, regulators, and physicians. Many of the manufacturing principles mentioned above are not applicable in production of cell therapeutics. Sterility of source materials cannot be guaranteed and the hitherto known procedures for sterilization are, as a rule, not feasible. Thus, the sterility of the final product cannot be guaranteed. Considering the extremely short shelf life of many cell therapeutics, sometimes only a few hours, the results from established methods for sterility testing are often available too late. Furthermore, the sterility of a test sample does not indicate sterility of the whole product. In most cases, conventional methods for pyrogen testing are not applicable for ATMPs. This paper demonstrates relevant limitations regarding microbial safety and pyrogenicity. Possibilities to overcome these problems are discussed and some novel solutions are proposed.

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.