The top film of the Petrifilm plate traps gas (seen as bubbles) produced by coliforms, providing “confirmed” counts.In addition, a glucoronidase indicator forms a blue precipitate around any E. coli colonies that may be present.
Note that E. coli O157:H7 is glucoronidase negative and will not produce a blue precipitate.
3M™ Petrifilm™ E. coli count provides results in 24 hours.
Note: Most E. coli (about 97%) produce beta-glucoronidase which produces a blue precipitate associated with the colony. The top film of the Petrifilm plate traps gas produced by the lactose fermenting coliforms and E. coli.
About 95% of E. coli produce gas, indicated by blue to red-blue colonies associated with entrapped gas on the Petrifilm EC plate (within approximately one colony diameter).
AOAC international and U.S. FDA Bacteriological Analytical Manual (BAM) define coliforms as gram-negative rods which produce acid and gas from lactose during fermentation.
Coliform colonies growing on the Petrifilm EC plate produce acid which causes the pH indicator to make the gel colour darker red.
Gas trapped around red coliform colonies on the Petrifilm plate indicates confirmed coliforms.
Quick and easy confirmed test results provide you with better information to make the right decisions. 3M™ Petrifilm™ E. coli/Coliform Count Plates provide the most cost-effective, convenient and reliable confirmation method for testing equipment, raw materials, food products and the manufacturing environment enabling you to monitor critical control points more frequently.
A survey of 274 plants who converted to Petrifilm Plates from traditional agar methods found an average labor savings of 45% and an average increased technician efficiency of 80%. The end result is higher quality product, better process control and an overall reduction in operational costs.