The dispensing stylus deposits decreasing amounts of sample as it moves from the center of the plate outwards. A logarithmically decreasing volume of sample is dispensed on the surface of a rotating Petri dish in an Archimedes spiral. The volume is calibrated and is known at every point of the Petri dish. The bacterial concentration is determined by dividing the number of colonies found by the volume dispensed in the same sector of the dish. The Spiral Plater deposits sample is five different deposition modes on both 100 mm and 150 mm plates.
Operation can be automatic, manual or semi automated.
Automatic mode features hands free cleaning and sample intake, while manual modes can be used to intake viscous or particulate samples or samples from nonstandard containers. Or by automated counting. Standard Exponential Mode Causes exponentially decreasing amounts of sample to be deposited for bacterial enumeration by spiral plating method and for single colony isolation. Also used to deposit antimicrobial agents in the Spiral Gradient Endpoint test and to produce a gradient of mutagenic substances in the Spiral Salmonella Assay. Slow Exponential Mode Used when plating organic compounds such as ethanol, or when using wet plates - prevents spirals from being splashed by centrifugal force.