Second collaborative study on analysis of bacteriophages in bathing waters

A second international collaborative study on bacteriophages in bathing waters was organised in March 1998. Fifteen European laboratories (including the organising laboratory) participated in the study. It consisted of two parts: (1) Analysis of naturally polluted standard samples for the enumeration of somatic coliphages (SOMCPH), F-specific phages (including the total number of the F-specific phages, FTOTPH, and the F-specific DNA phages, FDNAPH) as well as phages of Bacteroides fragilis (BFRPH); (2) Application of a concentration technique (based on flocculation) to a mixture of phage reference materials (oX174 for SOMCPH, MS2 for FTOTPH and B40-8 for BFRPH). In agreement with the participating laboratories, some of the data were excluded for further analysis because of technical problems in several laboratories. Analysis of the remaining data for the part of the study dealing with the naturally polluted standard samples resulted in values for the repeatability (r) varying from 1.63 - 2.34, and for the reproducibility (R) from 3.10 - 5.72 for the different groups of bacteriophages. The variation in these results was greater than those in which reference materials (with pure cultures of standard phages) were analysed. This was probably caused by a combination of extra Poisson variation in phage numbers in naturally polluted standard samples and the difficulties of interpreting plates of natural samples. Analysis of the results from the concentration technique showed low recovery of phage oX174 (2.2% - 16.4%), and variable recovery of phages MS2 (12.7 % - 99.4 %) and B40-8 ( 42.5% - 142.9 %)