Micro December 2018

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ISO 16649-2:2001

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All matrices were evaluated in a paired study design, and so all samples prepared for the 4

3M Petrifilm Rapid E. coli /Coliform Count Plate analysis in PSS were also used for the ISO 5

16649-2:2001 analysis. A 1.0 mL aliquot from each sample dilution was plated in duplicate onto 6

a Petri dishes. To each plate, 15 mL of TBX was added, swirled clockwise, then 7

counterclockwise, taking care to avoid spillage on the Petri dish lid and allowed to solidify. All 8

plates were inverted, incubated at 44 ± 1°C for 18–24 h and enumerated. If stressed cells were 9

used in the inoculation, TBX plates were incubated for 4 h at 37 ± 1°C followed by an incubation 10

of 18–24 h at 44 ± 1°C. The duplicate plates for each sample dilution were averaged, and then 11

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the average count was reported.

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Counts less than 150 typical colonies and less than 300 typical and nontypical colonies were

considered countable, while counts outside that range were considered estimates. Blue 14

colonies were enumerated as β -glucuronidase-positive E. coli colonies. These colonies did not 15

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require additional confirmation.

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Matrix Study Results

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A statistical analysis was conducted for each contamination level for each matrix evaluated

comparing the 3M Petrifilm Rapid E. coli /Coliform Count Plate to BAM Ch. 4 for total coliform 21

(non- E. coli coliform plus E. coli ) and E. coli , to ISO 4832:2006 for total coliform and to ISO 22

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