Bacteriophage Ecology Group

Bacteriophage Ecology Group Bacteriophage Ecology Group

Mixed-Indicator Method


Plaquing-based means of phage host-range assessment that involves testing the susceptibility of two strains of lawn bacteria simultaneously.

The mixed indicator method is particularly valuable for distinguishing phage mutants that display a host-range broadening versus a switch in host range. With simply a switch, or no change in host range at all, plaques will form but will be turbid since only one of the two indicator bacteria will be lysed. With host-range broadening, such that both bacterial strains now serve as phage hosts (or at least are both susceptible to phage-induced lysis), then plaques will be clear.

The mixed indicator method is one means by which plaque turbidity can occur. Note that such turbidity can occur also as a consequence of inadvertent lawn contamination with sufficient quantities of a phage-insusceptible bacterial strains or species.


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