A SIMPLE MEMBRANE FILTRATION-ELUTION METHOD FOR THE ENUMERATION OF F-RNA, F-DNA AND SOMATIC COLIPHAGES IN 100-ML WATER SAMPLES

A method which combines membrane filtration (MF) with a new swirling e lution (SE) procedure was developed for the enumeration of F-RNA, FDNA and somatic coliphages in 100 ml water samples. Using replicates of a diluted sewage seed, test methods were compared with overlay plate co unts. The method (ME-SE) involves 3 min sample filtration through a me mbrane filter, 6 min swirling of the filter in 2 ml of eluent, followe d by separate assay of the filter (face down on a host lawn) and eluen t (by overlay plating). The MF and eluent plate counts are then combin ed. By altering eluent composition (beef extract + NaCl and/or Tween 8 0), the following maximum recoveries were obtained, using tap water an d 0.45 mu m pore size filters: 72.9% for F-RNA coliphages (on host Sal monella typhimurium WG49), 81.5% for F-DNA coliphages (on E. coli RR), and 100.5% for somatic coliphages (on Escherichia coli 13706/60). Wit h 0.22 mu m filters, the equivalent recovery rates were 75.5, 92.2 and 99.8%, respectively. Using the optimum combination of filter pore siz e and eluent composition, the equivalent recovery rates were 75.2, 77. 1 and 85.1% from river water, and 45.9, 95.7 and 100.2% from sea water . It is concluded that the MF-SE method gives good recovery rates for all three phages from 100 mi samples of tap water and low turbidity fr esh waters, good recoveries of F-DNA and somatic coliphages from sea w ater, but poor recovery of F-RNA coliphages from sea water.