title: Cryopreservation reduces the concentration of detectable bacteria in contaminated peripheral blood progenitor cell products.
abstract: BACKGROUND
  Microbial contamination of PBPC products PBPCPs may cause severe clinical complications. There-fore, we investigated the influence of cryopreservation on the sensitivity to detect bacterial contaminations in PBPCPs.
  
  
  METHODS
  Expired PBPCPs (n = 29) were thawed, and defined concentrations of Staphylococcus epidermidis or Escherichia coli were inoculated into each bag. After 60 minutes of intermixing, a representative aliquot was drawn and cultured on Mueller-Hinton agar for 24 hours. Then, the products were cryopreserved for 24 hours, and the procedure was repeated as mentioned above. The total numbers of CFUs were counted before and after cryopreservation.
  
  
  RESULTS
  A mean concentration of 2529 CFUs per mL of S. epidermidis was determined before cryopreservation versus 2182 CFUs per mL after cryopreservation, demonstrating a decrease of detectable colonies (p < 0.05). For E. coli, the mean numbers were 424 CFUs per mL before cryopreservation and 343 CFUs per mL after cryopreservation, also showing a decrease (p < 0.05).
  
  
  CONCLUSIONS
  The cryopreservation reduces the concentration of detectable bacteria in contaminated PBPCPs. Especially in sterility testing of PBPCPs with low bacterial contamination, this phenomenon could lead to false-negative results with severe clinical consequences.
authors.affiliation: Institute of Medical Microbiology, the Institute of Transfusion Medicine/Transplantation Immunology, and the Department of Biometrics, University Hospital Münster, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Kipp
authors.forename: Elmar
authors.initials: E
authors.lastname: Linnemann
authors.forename: Rudolf-Josef
authors.initials: RJ
authors.lastname: Fischer
authors.forename: Walter
authors.initials: W
authors.lastname: Sibrowski
authors.forename: Uwe
authors.initials: U
authors.lastname: Cassens
mesh_terms: D001419:Bacteria / Q000302:isolation & purification*; D015925:Cryopreservation; D004926:Escherichia coli / Q000302:isolation & purification; D006412:Hematopoietic Stem Cells / Q000382:microbiology*; D006801:Humans; D013212:Staphylococcus epidermidis / Q000302:isolation & purification