EXPERIMENTAL FIGURE 5-44 Plaque assay. The plaque assay determines the number of infectious particles in a viral suspension. (a) A lesion, or plaque, develops where a single virion initially infected a single cell. Each plaque constitutes a pure viral clone. (b) Plaques on a lawn of Pseudomonas fluorescens bacteria made by bacteriophage ϕS1.

[Part (b) P. Rossi, 1994, Advances in biological tracer techniques for hydrology and hydrogeology using bacteriophages, Ph. D. thesis, University of Neuchatel, 200 pp. http://doc.rero.ch/record/2576/files/these_RossiP.]