Method of detecting gas-producing microbial colonies

A method, comprising:

• using an imaging device to produce a first image of a thin film culture device, the culture device having a front side having a transparent film cover sheet and a back side having a translucent substrate;
• wherein the first image is produced while providing illumination to the front side of the device;
• wherein the culture device comprises an indicator compound that is converted by a microorganism to a first product that is observable by a first color;
• wherein the culture device comprises a nutrient that can be converted to by a first type of microorganism to a gas;
• using the imaging device to produce a second image of the thin film culture device, wherein the second image is produced while providing illumination to the back side of the device;
• analyzing the first image to identify a microorganism colony at a first location in the culture device;
• analyzing the second image to identify a first gas bubble at a second location in the culture device;
• and
• determining whether the first location is within a predetermined distance from the second location.