Abstract

RIVM supported four laboratories with the introduction of the enumeration of F-specific RNA-bacteriophages. Six trials were organized to gain sufficient experience and to acquire comparable results between the participating laboratories. The following conclusions were drawn: - To achieve good and consistent results the technique should be applied regularly (preferably weekly). - The condition of host WG49 needs to be standardized by controlling density, growth rate, plasmid-segregation (kanamycine-sensitivity and resistance to nalidixic acid). - The laboratory-test according to Weiss et al. showed that all participants had acquired an acceptable technical level with the enumeration of FRNA-phages. The ideal case of plaque counts following a Poisson distribution was approximated with a pure culture of phage MS2. - Also it was shown that there was a high level of linearity in the range of 5 to 200 pfu per plate. - Differences between laboratories and whithin laboratories from time to time can remain limited to the optimal values for repeatability and reproducibility of 1.4-1.8 by performing the technique frequently, by standardizing the condition of host WG49, by using agar of optimal gelstrength, by using controlled media and by using standard samples of MS2. These values can however be much larger for other types of samples. - It is recommended for optimization to experiment with different agars and different agar-concentrations.