Micro December 2018

Coliform bacteria are a category of rod-shaped, non-spore forming Gram-negative bacteria. 1

These organisms can be motile or non-motile and can ferment lactose with the production of 2

acid and gas. While coliform bacteria are very common and normally harmless, coliform 3

contamination in food or beverage products does pose a health risk. Since coliforms are 4

commonly found in soil and vegetation, when coliform contamination is found, it usually is 5

caused by the environment. Coliform presence in food products raises the question of 6

pathogen contamination occurring through a similar process. Many coliforms, including E. coli , 7

a subgroup of coliform, can be found in the human digestive tract. While some strains of E. coli 8

are harmless, other strains can cause serious illness. Just like coliform, if E. coli contamination is 9

detected, this poses a greater risk for other pathogens to be present (4). 10

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Principle of the Method

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The 3M Petrifilm Rapid E. coli /Coliform Count Plate is a self-contained, sample-ready-

culture-medium system which contains a cold-water-soluble gelling agent and two different 15

indicators; 5-bromo-4-chloro-3-indolyl-D-glucuronide that indicates glucuronidase activity and 16

tetrazolium that facilitates colony enumeration. The 3M Petrifilm Rapid E. coli /Coliform Count 17

Plate is intended for the use for the enumeration of both E. coli and coliforms in various food 18

and beverage products and from environmental surfaces. The typical colony morphology for E. 19

coli is blue to blue-green colonies with or without gas production, regardless of size or color 20

intensity. Other coliform isolates will appear as red colonies with entrapped gas (within 21

approximately one colony diameter). The accurate quantitative range is less than or equal to 22

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