The Production of Plaques by Rhizobium Bacteriophage in Poured Plates and Its Value as a Counting Method

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Abstract
The bacteriophage used in this study was obtained by means of a strain- of nodule bacteria isolated from soil. The effect on plaque counts of external conditions such as temp. and length of incubation, the composition of the plating medium, the condition and number of the host bacteria and the number of viable phage were studied. Statistical examination of the results indicated that the modified plaque technique could be standardized so that reliable estimates could be made of 2 or more phage suspensions. Plaques develop by lysis of minute bacterial colonies throughout the agar. These colonies ceased to be susceptible to phage attack after about 24 hrs. of incubation at 25[degree]C, thus limiting the plaque size to the volume filled by phage diffusion within this time. Both the number and size of plaques were affected by the conc. of agar, the composition of the nutrients in the medium, the temp. of incubation and the age of the bacterial suspension used for plating.

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