Abstract
The standard method for the enumeration of somatic coliphages in water proposed by the American Public Health Association recommends the use of single layer plaque assays with 5 ml sample and the direct use of frozen and thawed host E. coli cultures. In assays of spiked river water the efficiency of plating (e.o.p.) of the standard method, using frozen/thawed host cultures, was significantly lower than comparable assays using unfrozen host cultures. Frozen/thawed cultures also produced significantly lower efficiency of plating in scaled up versions of the standard method using both 50 and 100 ml sample. The e.o.p. varied from 39.0–46.1% with frozen/thawed cultures and 67.7–74.4% with unfrozen cultures at OD 0.5, relative to overnight cultures. It is therefore recommended that overnight cultures are used in place of frozen/thawed cultures in the APHA standard method and scaled up versions of it.
Published Version
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