title: Rapid detection of contaminant bacteria in platelet concentrate using differential impedance.
abstract: OBJECTIVE
  Current FDA-approved culture-based methods for the bacterial testing of platelet concentrate (PC) can yield false-negative results attributed to Poisson-limited sampling errors incurred near the time of collection that result in undetectable bacterial concentrations. Testing PC at the point of issue (POI) extends the incubation period for any contaminant bacteria increasing the probability of detection. Data are presented from time-course experiments designed to simulate POI testing of bacterially contaminated PCs at different stages of growth using differential impedance sensing.
  
  
  METHODS
  Whole-blood-derived PCs were typically spiked with low numbers of bacteria (approximately 100 CFU/ml) and incubated under standard PC storage conditions. Each infected unit was evaluated every two hours over a 12-h period. All samples were treated with a chemical compound that induces stress in the bacterial cells only. The development of any bacterial stress was monitored by detecting changes in the dielectric properties of the PC using differential impedance.
  
  
  RESULTS
  Differential impedance measurements and corresponding cell counts at the different time-points are presented for six organisms implicated in post-transfusion-septic reactions. All infected PCs were detected once contaminant bacteria reached concentrations ranging between 0·6 × 10(3) and 6 × 10(3)  CFU/ml irrespective of the phase of growth. Results were obtained within 30 min after the start of the assay and without the need for cell lysis or centrifugation.
  
  
  CONCLUSIONS
  Differential impedance sensing can detect bacterial contamination in PC rapidly at concentrations below clinical thresholds known to cause adverse effects.
authors.affiliation: BioSense Technologies, Inc., Woburn, MA, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Zhao
authors.forename: A
authors.initials: A
authors.lastname: Chalmers
authors.forename: R
authors.initials: R
authors.lastname: Rieder
mesh_terms: D001792:Blood Platelets / Q000382:microbiology*; D017097:Electric Impedance; D004926:Escherichia coli / Q000502:physiology; D006801:Humans; D007711:Klebsiella pneumoniae / Q000502:physiology; D057230:Limit of Detection; D008089:Listeria monocytogenes / Q000502:physiology; D017713:Platelet Transfusion / Q000009:adverse effects; D018805:Sepsis / Q000209:etiology / Q000517:prevention & control; D012706:Serratia marcescens / Q000502:physiology; D013211:Staphylococcus aureus / Q000502:physiology; D013212:Staphylococcus epidermidis / Q000502:physiology
keywords: bacterial detection; dielectric permittivity; differential impedance sensing; platelet contamination; stress response