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

Development of a proof of principle for universal neutralization of antibiotics in cord blood by-products used for sterility testing

BACKGROUND

Bacterial contamination of cord blood (CB) represents a safety risk for transplantation patients. CB sterility testing at Canadian Blood Services' Cord Blood Bank is performed using a 1:1 mix of CB-derived plasma and red blood cells (RBCs). Culture bottles of an automated culture system, which lack antimicrobial neutralization properties, are used for bacterial screening of CB. This process is unsuitable for CB-containing antibiotics, potentially resulting in false-negative results. This study was aimed at developing a protocol for antibiotic neutralization in CB used for sterility testing.

STUDY DESIGN AND METHODS

Phase 1: four neutralizers-penicillinase, ion exchange resins L and A, lecithin + Tween80, and activated charcoal (AC)-were individually tested to neutralize penicillin or gentamicin in cultures of Staphylococcus epidermidis or Klebsiella pneumoniae, respectively, adjusted to 100 colony forming units/mL, in Müller-Hinton broth (MHB). Phase 2: combinations of penicillinase plus resin L or penicillinase plus AC were assayed for the simultaneous neutralization of both antibiotics in MHB. Phase 3: penicillinase plus resin L was used to neutralize both antibiotics in CB sterility testing samples (plasma + RBCs).

RESULTS

Phase 1: penicillin was neutralized by penicillinase and resin A, while gentamicin was neutralized by resin L and AC. Phase 2: the antibiotics were simultaneously neutralized by the two neutralizer combinations tested. Phase 3: neutralization of both antibiotics in CB was achieved with penicillinase and resin L.

CONCLUSION

A protocol for antibiotic neutralization in CB sterility testing samples has been successfully developed at Canadian Blood Services' Cord Blood bank. This in-house assay applies to any culture-based CB bacterial screening method.

Optimization of cord blood unit sterility testing: impact of dilution, analysis delay, and inhibitory substances

BACKGROUND

Different methods are used by cord blood banks to prepare samples for sterility testing. Suboptimal methods can result in the release of contaminated products. In our organization, samples are prepared by diluting the final product in RPMI-1640 medium. In this work, we have compared our method with different approaches to verify whether optimization should be sought.

STUDY DESIGN AND METHODS

Cord blood units (n = 6 units per bacterial strain) characterized to contain inhibitory substances or not were inoculated (10 colony-forming units/mL) with Streptococcus agalactiae, Staphylococcus epidermidis, Klebsiella pneumoniae, Escherichia coli, or Bacteroides fragilis. After plasma and red blood cell removal, stem cell concentrates were diluted in RPMI-1640, thioglycollate, or the unit's plasma. These products, as well as final product, plasma, and red blood cell fractions, were held from 0 to 72 hours at 20 to 24°C before inoculation in culture bottles and detection using the BacT/ALERT 3D system.

RESULTS

Dilution of cell concentrates in RPMI-1640 allowed bacterial detection in 93.3% of noninhibitory cord blood samples after a 24-hour storage period. Thioglycollate medium better promoted bacterial growth in inhibitory cord blood samples that were held for 72 hours before testing (66.7%) compared with RPMI-1640 (45.0%). Less than 33% of all spiked plasma samples were detected by the BacT/ALERT 3D system.

CONCLUSION

Diluting cord blood samples in culture medium containing bacterial growth promoting substances is a suitable option for sterility testing, whereas the use of plasma should be proscribed, because it might lead to false-negative results. Because inhibitory substances affect bacterial growth, inoculation of culture bottles should be done rapidly after sample preparation.

Comprehensive detection and identification of bacterial DNA in the blood of patients with sepsis and healthy volunteers using next-generation sequencing method - the observation of DNAemia

Blood is considered to be a sterile microenvironment, in which bacteria appear only periodically. Previously used methods allowed only for the detection of either viable bacteria with low sensitivity or selected species of bacteria. The Next-Generation Sequencing method (NGS) enables the identification of all bacteria in the sample with their taxonomic classification. We used NGS for the analysis of blood samples from healthy volunteers (n = 23) and patients with sepsis (n = 62) to check whether any bacterial DNA exists in the blood of healthy people and to identify bacterial taxonomic profile in the blood of septic patients. The presence of bacterial DNA was found both in septic and healthy subjects; however, bacterial diversity was significantly different (P = 0.002) between the studied groups. Among healthy volunteers, a significant predominance of anaerobic bacteria (76.2 %), of which most were bacteria of the order Bifidobacteriales (73.0 %), was observed. In sepsis, the majority of detected taxa belonged to aerobic or microaerophilic microorganisms (75.1 %). The most striking difference was seen in the case of Actinobacteria phyla, the abundance of which was decreased in sepsis (P < 0.001) and Proteobacteria phyla which was decreased in the healthy volunteers (P < 0.001). Our research shows that bacterial DNA can be detected in the blood of healthy people and that its taxonomic composition is different from the one seen in septic patients. Detection of bacterial DNA in the blood of healthy people may suggest that bacteria continuously translocate into the blood, but not always cause sepsis; this observation can be called DNAemia.

Molecular characterization of microbial contaminants isolated from Umbilical Cord Blood Units for transplant

Disposal of Umbilical Cord Blood Units due to microbial contamination is a major problem in Cord Blood Banks worldwide as it reduces the number of units available for transplantation. Additionally, economic losses are generated as result of resources and infrastructure used to obtain such units. Umbilical Cord Blood Units that showed initial microbial contamination were subject to strains isolation, identification, and characterization by sequencing the 16S rRNA gene and Enterobacterial Repetitive Intergenic Consensus (ERIC-PCR). Moreover, tests of antimicrobial resistance/sensitivity and phenotypic activities that may play an important role in microbial infection were performed. Microbial contamination was detected in 120 Umbilical Cord Blood Units (2.31%) in the period from 2003 to 2013. The most frequently isolated strains were Enterococcus faecium, followed by Staphylococcus epidermidis, Escherichia coli, Enterococcus faecalis, Staphylococcus haemoliticus, Klebsiella pneumoniae, Enterococcus durans, Lactobacillus helveticus, Enterococcus hiriae and Roseomonas genomospecies 5. The ERIC-PCR assays revealed a wide genetic diversity in some strains although belonging to the same genus and specie, indicating different sources of contamination. Broad-spectrum penicillins, third generation cephalosporins, aminoglycosides, and fluoroquinolones showed lower inhibitory activity on the tested strains. All strains were proteolytic, 67.69% were amylase-positive, 27.6% hemolysis-positive, and 34.71% nuclease-positive. The most common sources of contamination were: vaginal flora, digestive tract, and skin flora, highlighting the need for staff training in good manufacturing practices in collection SCU since all contaminants identified are part of the microbial flora of the donors. Implications and consequences in the therapeutic use of Umbilical Cord Blood Units for transplantation contaminated by multiresistant bacteria in immunocompromised patients are discussed.

Antimicrobial activity in cord blood units: occurrence and levels of antibiotics

BACKGROUND

Antibiotic prophylaxis treatment at delivery is highly recommended for reducing the risk of infection for mothers positive for group B streptococcus. It is therefore expected that some cord blood (CB) products will contain residual antibiotics. This study aimed to determine the incidence and level of β-lactam antibiotics in CB products.

STUDY DESIGN AND METHODS

The antimicrobial activity of 60 CB plasma by-products was evaluated using disk diffusion assays on 10 bacteria species. Plasma samples showing antimicrobial activity were either treated with β-lactamase enzyme to inhibit β-lactam antibiotics or heated to 56°C for 30 minutes to inhibit complement proteins. β-Lactam antibiotic concentrations were determined by comparison with a standard curve obtained with known concentrations of antibiotics.

RESULTS

Antimicrobial activity against mostly Gram-positive microorganisms was observed in 33% of CB units. The β-lactamase enzyme abolished the antimicrobial activity in the majority of these CB products. Up to 5 μg/mL penicillin and 14 μg/mL ampicillin were measured in these products.

CONCLUSION

Approximately one-third of CB products contain significant amounts of plasma with residual antibiotics, which can affect the survival and growth of bacterial contaminants when performing the sterility test and potentially lead to false-negative results. Additional work is required to better understand whether residual antibiotics in CB affect penicillin-allergic patients.