n. (Microbiology) an instrument designed to conveniently count or assist counting colonies{ 9 } of microorganisms on a plate containing a gelled growth medium. One variety uses a pencil-like rod with a metal tip, which is connected by an electrical connection to the gelled growth medium; when touched to a colony{ 9 } on the plate, the completion of the electrical circuit causes an increment of 1 unit on the readout of the colony counter. [ PJC ]