Q-174. Sampling Aerosols of Bacteriophages with Polycarbonate and PTFE Filters

D. Verreault, G. M. Rousseau, S. Moineau, C. Duchaine;
Univ. Laval, Quebec, QC, CANADA.

Many types of filters have been used to sample airborne viruses. Liquid impingers as well as a variety of other samplers are often used but only filters can efficiently trap both large and small particles. The choice of filter should not only depend on the efficiency of capturing airborne viruses but also on the potential output of the subsequent analysis. The latter is influenced by the ability to elute the viruses from the filter and by preserving viral infectivity after sampling. In this study, two types of filters were compared; polytetrafluoroethylene (PTFE) and polycarbonate (PC). Their efficacy was studied using the coliphage phiX174 (single-stranded DNA genome, icosahedral capsid without a tail) and the lactococcal phage P008 (double-stranded DNA genome, icosahedral capsid with a long non contractile tail). Both viruses were nebulized simultaneously in an aerosol chamber and were sampled with three PTFE and three PC filters. Aerosol size and concentration were monitored with an aerodynamic particle sizer and the mean mass diameter was 1.5 µm. After sampling, filters were eluted with water and detergent and the liquid was analyzed by qPCR (number of genomes) and plaques (number of infective phages). This experience was repeated six times. For both viruses, qPCR results were comparable with PC and PTFE filters. Similarly, phage titers for phiX174 showed no difference with both filters. However, a significant difference in the phage titers was noted with P008 as PC filters were 3-fold more efficient than PTFE filters. Finally, comparison between qPCR results and phage titers indicated that the nebulization/filtration/elution led to a 2-fold and a 2-log reduction in the number of infective particles of P008 and phiX174, respectively. Our data indicate that i) PTFE and PC filters can efficiently recover airborne P008 and phiX174 phages, ii) the capacity of preserving viral infectivity varies depending on the filter and the virus sampled, iii) sampling by filtration/elution can lead to significant virus inactivation, iv) detection of airborne viruses will likely require a case by case analysis to determine the best sampling method.