title: Recovery balance: a method for estimating losses in a Bacillus anthracis spore sampling protocol.
abstract: OBJECTIVE
  The aim of this study was to develop a method to calculate the performance, and isolate error contributions occurring in a microbial surface sampling protocol.
  
  
  RESULTS
  The experiments were conducted using a slip/peel tester to provide consistent pressure during the wipe collection. Fluorescence microscopy was used to count spores deposited on the coupon prior to sampling. The mean recovery efficiency (RE) as well as the efficiency of each step in the process was estimated by a recovery balance (RB), similar to a mass balance. Two studies were conducted in this work. In the first one, the recovery of spores from the solution (RE(soln)) was 57.7% (SD = 8.0), while spores left on the glass surface after wiping (RE(b+c)) was 2.8% (SD = 2.4). The RE of spores adhered to the tube wall (RE(tube)) and glass surface (RE(surf)) was 1.2% (SD = 19.6) and 5.8% (SD = 7.1), respectively. From the recovery balance, it was determined that 39.9% (SD = 21.2) of spores were lost to the wipe (RE(wipe)). The applicability of the RB method was demonstrated in a second study by examining the relative impact of parameters affecting spore collection including relative humidity, wipe material, wetting agent and nonporous surfaces.
  
  
  CONCLUSIONS
  The approach used in this study pointed out the need for a closer analysis of the complex interaction between spores and wipe material because a substantial percentage of spores were lost to the wipe.
  
  
  CONCLUSIONS
  The recovery balance, in association with independent controls, provides an account for error contribution and potential variability on each step of the sampling protocol. The approach is not meant to be a replacement for field or laboratory validation of wipe recoveries but promote the development of new collection methodologies and support protocol optimization in laboratory settings.
authors.affiliation: Biosystems and Biomaterials Division, Material Measurements Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8315, USA. sdasilva@nist.gov
authors.forename: S M
authors.initials: SM
authors.lastname: Da Silva
authors.forename: A A
authors.initials: AA
authors.lastname: Urbas
authors.forename: J J
authors.initials: JJ
authors.lastname: Filliben
authors.forename: J B
authors.initials: JB
authors.lastname: Morrow
mesh_terms: D001408:Bacillus anthracis / Q000302:isolation & purification*; D001431:Bacteriological Techniques / Q000379:methods*; D004783:Environmental Microbiology; D008856:Microscopy, Fluorescence; D013048:Specimen Handling / Q000379:methods*; D013171:Spores, Bacterial / Q000302:isolation & purification*