Abstract: The contrast chamber for spotlighting bacterial colonies with respecto to their culture medium performs the automatic counting, through the use of an automatic processor connected to a reading head (7), of bacterial colonies which develop in the capsules wherein the culture takes place; additionally, it also provides for the automatic introduction of the capsules (5) inside the contrast chamber The contrast chamber is provided with lateral lighting means, using the light reflected by a reflection tube (2) and emitted by a lighting source (1) postioned above the capsule (5) which has been closed by a lid provided with an opaque disc (3). The reading head (7) is positioned under the capsule (5) and is associated to a second light source (8) which moves together with the reading head and which is inclined with respect to the surface of the capsule (5), so that the light beams do not impinge on the reading head (7).