Influence of harvest bacterial contamination on autologous peripheral blood progenitor cells post-transplant

Successful autologous hematopoietic stem cell transplants using Salmonella positive products collected from asymptomatic donors

BACKGROUND

Bacterial contamination of hematopoietic stem cell (HSC) products is most commonly due to normal skin flora. Salmonella in HSC products is rare, and to our knowledge safe administration of an autologous HSC product containing Salmonella has not been reported.

STUDY DESIGN AND METHODS

We describe two patients undergoing autologous HSC transplant: peripheral blood HSC collection was performed by leukapheresis, and samples were cultured according to standard institutional protocol. Subsequent microorganism identification was performed using MALDI-TOF (Bruker Biotyper). Strain-relatedness was investigated by infrared spectroscopy using the IR Biotyper (Bruker).

RESULTS

The patients were asymptomatic throughout the collection process; however, HSC products collected on two consecutive days from each patient were positive for Salmonella. Isolates from both cultures were further characterized as Salmonella enterica serovar Dublin by the local public health department. Antibiotic susceptibility testing revealed different sensitivity patterns for the two strains. IR Biotyper demonstrated significant discriminatory power among the clinically significant Salmonella enterica subspecies, serogroups B, C1, and D. The patient strains were similar as both belonged to Group D Salmonella enterica serovar Dublin but were not identical. The Salmonella positive autologous HSC products were infused to both patients following administration of empiric antibiotic therapy. Both patients successfully engrafted and did well.

CONCLUSION

Salmonella is rarely seen in cellular therapy products and positivity may be the result of asymptomatic bacteremia at the time of collection. We present two instances of autologous HSC products containing Salmonella that were infused, along with prophylactic antimicrobial therapy without significant adverse clinical effects.

An intermittent outbreak of Burkholderia cepacia contaminating hematopoietic stem cells resulting in infusate-related blood stream infections

Microbial contamination of hematopoietic stem cells (HSC), used for autologous and allogenic transplantations, is rare but could cause serious blood stream infection in transplanted patients. These infections occur immediately, or later following the formation of biofilm on the catheter lumen. The present study describes an intermittent B. cepacia HSC contamination associated with nosocomial bacteremia: from October 2011 to April 2015, 17 B. cepacia strains were isolated in HSC bags (n = 14) and blood cultures (n = 3) in patients hospitalized in the National Bone Marrow Transplant Center. Two epidemiologic investigations in the National Blood Transfusion Center, allowing the isolation of three strains in hygiene samples, and four interventions in this institution were done. To identify the source of this contamination, a molecular investigation was done on 23 B. cepacia strains isolated in our center from 2007 to 2015. PFGE analysis revealed five clusters. The major cluster included 18 strains isolated from HSC bags (n = 14), blood culture (n = 1), and water cans and bath (n = 3). The second cluster (B) including only two and the remaining clusters (C, D, and E) contained single strains isolated before the epidemic period. These findings confirmed that the origin of the outbreak was the contaminated water used in the water bath during the thawing step of HSC bags. Based on this result, new sterile water was used for every defrosting, but HSC bags contamination persisted. In May 2015, the water bath was replaced with a dry bath and no B. cepacia strain was isolated from that date to April 2020.

Effects of cryopreservation on gram-positive bacteria contaminants in umbilical cord blood

OBJECTIVE

To evaluate the effects of cryopreservation in post-thaw umbilical cord blood units for the survivability of Gram-positive bacteria strains.

BACKGROUND

Microbial screening is required for all cord blood units (CBUs). Four gram-positive contaminants were documented to survive cryopreservation poorly and isolation of other contaminants were reported.

METHODS

Forty-eight contaminated CBUs detected with either Staphylococcus epidermidis, Corynebacterium species, Peptostreptococcus or Streptococcus species before cryopreservation were used in this study. CBUs were processed, DMSO-infused and microbial screened before cryopreservation. Post-thaw microbial screening was achieved using 1 and 10 ml inoculants in BACTEC culture bottles. Positive bottles were subjected for microbial identification and results were compared with those from pre-freeze.

RESULTS

A higher rate of microbial contamination was found using the 10 ml inoculant. Screening of 11 CBUs did not detect any contaminants while 30 CBUs screened detected more than one unknown contaminants and majority of contaminants were identified to be gram-negative species.

CONCLUSION

A higher inoculation volume used at post-thaw for microbial screening improves contamination detection but leads to the loss of precious cord blood. Some contaminants did not survive cryopreservation or were not identified due to their low microbial levels. Contrasting contaminants found at post-thaw suggest the improvements made in detection and identification of contaminants over the years.

Impact of microbial contamination of haematopoietic stem cells on post-transplant outcomes: A retrospective study from tertiary care centre in India

BACKGROUND

Haematopoietic stem cells (HSC) may act as a source of infection for the recipient due to manipulation at multiple levels from collection to infusion. Due to the high risk of contamination cultures are usually taken during multiple steps. The clinical significance of microbial contamination of HSC on the post-transplant course and the role of prophylactic antibiotics is relatively unknown.

AIMS AND METHODS

The aim of our study is to investigate the incidence of microbial contamination of haematopoietic stem cell and to assess its impact on the post-transplant febrile neutropenia, engraftment kinetics, hospitalisation and day 100 mortality. Details of all patients admitted in the bone marrow transplantation unit of a tertiary care centre in India between January 2014 and December 2018 were collected from case records.

RESULTS

Of the 1306 stem cell harvests from 503 patients sent for culture, 17 harvests (1.3%) were found to have a culture positive report. Sixteen patients had undergone autologous transplant. Multiple myeloma was most common indication of HSC transplant followed by Non-Hodgkin Lymphoma (NHL). Twelve of 17 HSC cultures were positive at the time of infusion and five were positive at the time of harvest. The five HSC that were culture positive at the time of harvest were culture negative at the time of infusion. Gram-positive organisms were isolated in six cultures and gram-negative in rest. All patients developed febrile neutropenia post-transplantation between day 1 and day 7. The median time of onset of fever was day +5 (1-7), the median duration of fever was 4 days (2-7), the median duration of antibiotic use was 11 days (9-16). Median day for neutrophil engraftment was 11 days (9-16), the median day for platelet engraftment was 14 days (10-25) and median duration of hospitalisation was 15 days (12-78). All patients were alive at day 100 of transplant.

CONCLUSION

This study shows that there appears to be minimal impact of culture positive HSC on transplant related outcomes in terms of engraftment kinetics, duration of hospitalisation and day 100 mortality. Discarding of contaminated HSC may not be required, though on development of febrile neutropenia appropriate antibiotics should be administered based on sensitivity pattern of HSC culture. Larger prospective studies are needed to determine the clinical relevance of such contaminations. Emphasis should be laid on better infection control practices to minimise contamination rates.

Bacteremia During Early Post-allogeneic Hematopoietic Stem Cell Transplantation Period: A Single Center Experience

Bacteremia is a significant complication of allogeneic hematopoietic stem cell transplantation (HSCT). We aimed to study bacteremia occurring during early post-transplant period at Bone Marrow Transplantation Unit of Ain Shams University regarding its risk factors and impact on survival. Patients performing allogeneic HSCT were followed up for occurrence of bacteremia. Survival status was assessed at 180 days post-transplant. Bacteremia occurred in 53.3 % of patients. On univariate analysis, CD34 +ve cell dose (P = 0.004), duration of neutropenia (P = 0.018), time interval between day of stem cell infusion and day of neutrophil engraftment (P = 0.043) and > 1 apheresis days (P = 0.040) were associated with higher rates of bacteremia. On multivariate analysis, CD34 +ve cell dose (P = 0.002) and apheresis day number (P = 0.038) remained significant. There was significant difference between patients who developed bacteremia and those who did not regarding overall survival (OS) (P = 0.042). Patients developing bacteremia caused by Gram negative bacteria (GNB) had lower OS than Gram positive bacteria (GPB) (P < 0.001). In conclusion, stem cell dose and apheresis day number influence bacteremia risk. Also, Gram negative bacteremia has negative impact on allogeneic transplant recipient survival rates.

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.

Microbial screening of unrelated cord blood units in a Chinese cord blood bank

BACKGROUND

Given limited sample volume available for sterility testing, optimal testing methods and algorithms of cord blood (CB) have not been established according to standards.

STUDY DESIGN AND METHODS

The volume of CB unit was reduced to 20 mL in a closed system. Hetastarch and cryopreservation solution was added to the processed CB unit in Class 100 environment. In the routine sterility testing, 20 mL of red blood cells (RBC) sample was cultured in aerobic and anaerobic culture bottles. In verification post-thaw culture of the final product, some of the discarded final product units were also sampled and cultured after thaw. All the culture bottles were incubated in the BacT/ALERT 3D system.

RESULTS

In the routine sterility testing, 139 of 7032 CB units (1·98%) were contaminated with microorganism. In 84 of these 139 units (60·4%) only the anaerobic bottle was positive. Lactobacillus spp. were the most prevalent contaminant. Sixty-two discarded CB stem cell units were recultured after thaw. Of these, 10 of 48 units with a positive culturing of RBC sample were negative in the post-thaw reculture. One of 14 units with negative culturing of RBC sample was contaminated with Bifidobacterium breve in special verification test.

CONCLUSION

Our study demonstrates the predominant organisms implicated in CB microbial contamination were part of the human intestinal and vaginal flora. The larger sample volume and anaerobic culture would significantly increase the detection rate of microbial contaminated CB. We also found that potential transfusion-transmitted bacterial infection risk still existed in final product although microbial screening was performed.

Optimization of microbial screening for cord blood

BACKGROUND

Collection and processing of cord blood (CB) is associated with significant risk of contamination; hence standards mandate microbial screening of the final product. The sensitivity of current methods to evaluate the microbial content of CB is unknown, given the small volume tested and reduced sensitivity of pediatric bottles. Hence, this study was undertaken to evaluate an optimal microbial screening method.

STUDY DESIGN AND METHODS

CB was collected using a closed system then spiked with organisms at 1 or 10 colony-forming units (CFUs)/mL. Samples were screened using culture bottles (BacT/ALERT, bioMérieux; and BACTEC, Becton Dickinson). Several methods were evaluated with different combinations of inoculated bottles (adult vs. pediatric), sample types (plasma discard, red blood cell [RBC] discard, or final product), and sample volumes.

RESULTS

Of 94 cord blood units (CBUs) spiked with organisms before screening, 81% tested positive for contamination overall. Screening of CB in pediatric bottles resulted in equivalent detection rates on the BacT/ALERT and BACTEC systems (33% at 1 CFU/mL and 73% at 10 CFUs/mL, respectively). However, the pediatric bottle screen only detected 15% of obligate anaerobes. A combined fraction method showed superior detection (71%) compared to the plasma fraction (27%) and resulted in optimal anaerobic detection.

CONCLUSIONS

This study demonstrates that the optimal microbial screening method for CB includes testing a combination of discard fractions (plasma and RBCs) in addition to final product using an automated culture system. Inoculating a small sample of final product in a pediatric bottle is suboptimal for microbial detection and may lead to distribution of contaminated CB for transplantation.

Effects of cryopreservation on microbial-contaminated cord blood

BACKGROUND

Cord blood units (CBUs) are associated with significant risk of exposure to microbial contamination during collection and processing; however, the survival of bacteria within a CBU is poorly understood. This study aimed to determine whether contaminating organisms in CBU survive the cryopreservation, frozen storage, and subsequent thawing conditions before infusion.

STUDY DESIGN AND METHODS

A total of 134 CBUs rejected from banking due to known contamination were thawed and rescreened using blood culture bottles (BacT/ALERT, bioMérieux). An additional 61 fresh CBUs were deliberately spiked with a range of microbial organisms and evaluated both before freeze and after thaw.

RESULTS

Microbial contaminants were detected after thaw in 63% of stored contaminated CBUs and 85% of spiked CBUs. Postthaw organism detection in spiked cord blood (CB) was higher in adult culture bottles (80%) than pediatric culture bottles (61%). Twenty percent of spiked organisms, particularly Bacillus subtilis, Escherichia coli, Clostridium sporogenes, and Propionibacterium acnes, were not detected in prefreeze samples but were detectable after thaw.

CONCLUSIONS

This study demonstrates that the majority of contaminating organisms isolated in a prefreeze sample of CB have the ability to survive cryopreservation, frozen storage, and thawing. Further, CBUs reported as microbial free may contain microbial contamination, which could result in transplantation of contaminated CB and be potentially deleterious to a patient.

Factors affecting microbial contamination rate of cord blood collected for transplantation

BACKGROUND

Collection and processing of cord blood (CB) is associated with significant risk of microbial contamination and hence relevant standards mandate microbial screening of the final product. This study aimed to determine the contamination rate and associated risk factors during 14 years of banking at the Sydney Cord Blood Bank.

STUDY DESIGN AND METHODS

CB was collected and processed using a closed system and tested for contamination using blood culture bottles (BacT/ALERT, bioMérieux) incubated for a minimum of 5 days. Four microbial screening methods were used with different combinations of inoculated bottles (adult or pediatric) and associated sample volumes (10 or 1 mL).

RESULTS

Of 13,344 CB units screened, 537 (4.0%) tested positive for contamination, with Bacteroides spp. (20.9%), Staphylococcus spp. (18.6%), and Propionibacterium spp. (13.7%) being the most common isolates. The contamination rate reduced from 10% in 1997 to 1.1% in 2009. Multivariate analysis demonstrated the following variables were independently associated with higher contamination rates: vaginal delivery, collection by obstetric staff, and use of an anaerobic bottle in addition to an aerobic bottle (which facilitated a larger sample inoculation volume than pediatric bottles).

CONCLUSIONS

This study demonstrates that contamination rates of CB collected for transplantation can be substantially reduced by collection after cesarean delivery and utilizing trained CB collection staff. These data also indicate that the common practice of testing using a pediatric (aerobic) bottle with its attendant small volume of the final CB product may be suboptimal for sensitive detection of contaminating anaerobic microbes.

Sterility testing of hematopoietic progenitor cell products: a single-institution series of culture-positive rates and successful infusion of culture-positive products

BACKGROUND

Administration of culture-positive hematopoietic progenitor cells (HPCs) causing adverse events has been a hypothesized yet largely unmeasured risk of the clinical practice of HPC transplantation. To enhance patient safety, the FDA has issued regulations prohibiting the use of culture-positive HPCs. Numerous studies have reported the infusion of culture-positive HPCs; however, the low frequency of adverse events prevents accurate determination of this risk.

STUDY DESIGN AND METHODS

Product culture results and clinical outcomes from January 1998 through March 2006 representing 7233 HPC collections for 2118 transplants at a single institution were reviewed.

RESULTS

A total of 119 units of HPCs (1.6%) intended for 95 patients were culture-positive. Of the 69 patients transplanted with culture-positive HPCs, 5 received products with cultures pending, and 64 received products with the positive culture results known. One of 69 patients had a new positive blood culture 5 days after infusion with the same species as the product. There was not a clinically relevant difference in the rate of infusion-related symptoms reported for patients who received culture-positive products compared to all infusions. The survival of patients who received culture-positive products (n = 69) was not different from all HPC recipients (n = 2046; p = 0.419).

CONCLUSION

No infusion-related risks of culture-positive HPCs to patient safety were identified. Our data suggest that the decision to use culture-positive HPCs must be made in the context of the global risks associated with transplants such as remobilization, replacement product availability, and the nature of the organism.