Thanks to everyone who has responded so far (and to those who might still respond). I think the best solutions I've seen so far were Howard Shapiro's solution of using anti-vaccinia antibodies (PE conjugated) and (even better, although technically more difficult) putting various pfu concentrations of virus under an electron microscope and counting. Some of you commented that you weren't sure that the pfu/particle ratio wasn't that important. At this point it is unknown what effect it has - but we have routinely seen viable bacteria counts by flow that are 1-2 logs higher than the colony counts after aerosol sprays. At this point it is interesting information, but the relevance is unclear. Howard - you are right, we could count vaccinia directly by flow given the large size of poxviruses. I am attempting to develop the beads as a more generally adaptable technique to the wide variety of viruses we study here - not just vaccinia but also the more exotic filoviruses which are considerably smaller. Currently most researchers use vero plaque assays to determine the pfu of the virus, which is certainly a proven technique but requires considerable time and effort whereas the beads could be done the same afternoon as the spray. Many thanks again to all those who replied! Douglas S. Reed, Ph.D. Microbiologist Department of Aerobiology and Product Evaluation Division of Toxinology and Aerobiology U.S. Army Medical Research Institute of Infectious Disease 1425 Porter St. Ft. Detrick Frederick, MD 21702-5011 301-619-6728 301-619-2541 fax Doug.Reed@det.amedd.army.mil
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