An Automatic System for Enumeration of Colony-Forming Units by the Surface Plate Method

A device for mechanical dilution and application of specimens and counting microbial colonies was developed. The device consists of a transport apparatus which transports petri dishes from one side of the apparatus to the other in such a way that the plate and lid of petri dishes are entirely separated at a particular stage. A diluting and inoculating system performs 10-fold dilutions of specimens from 10-1 to 10-8 dilutions and inoculation of the diluents. The inoculum is applied to the agar surface of preselected petri plates by an application system. Both a diluting and inoculating system and an application system can be connected to the apparatus. In this way a maximum of 25 agar plates can be handled. This new automatic system for enumeration of colony-forming units by the surface plate method is more accurate and reliable than the customary conventional methods.