Recovery balance: a method for estimating losses in a Bacillus anthracis spore sampling protocol
Article first published online: 27 DEC 2012
© 2012 No claim to US Government works
Journal of Applied Microbiology
Volume 114, Issue 3, pages 807–818, March 2013
How to Cite
Da Silva, S.M., Urbas, A.A., Filliben, J.J. and Morrow, J.B. (2013), Recovery balance: a method for estimating losses in a Bacillus anthracis spore sampling protocol. Journal of Applied Microbiology, 114: 807–818. doi: 10.1111/jam.12090
- Issue published online: 18 FEB 2013
- Article first published online: 27 DEC 2012
- Accepted manuscript online: 4 DEC 2012 11:43AM EST
- Manuscript Accepted: 20 NOV 2012
- Manuscript Revised: 2 NOV 2012
- Manuscript Received: 21 AUG 2012
- Interagency Agreement. Grant Number: HSHQDC-09-X-00457
- National Institute of Standards and Technology (NIST)
- Bacillus anthracis Sterne;
- fluorescence microscopy;
- spore counting;
- surface sampling
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.
Methods and 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 (REsoln) was 57·7% (SD = 8·0), while spores left on the glass surface after wiping (REb+c) was 2·8% (SD = 2·4). The RE of spores adhered to the tube wall (REtube) and glass surface (REsurf) 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 (REwipe). 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.
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.
Significance and Impact of the Study
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.