ERP Micro December 2019

0.2–2 cfu/ 375g25g 2–10 cfu/ 375g25g 0 cfu / 3 25g 0.2–2 cfu/ 3 25g 2–10 cfu/ 3 25g

20

375g25g

Raw ground beefFresh vegetables Raw ground beefFresh vegetables

5

375g25g

5

3 25g 3 25g 3 25g

MLG 5.09BAM Chapter 4A

E. coli O157:H7

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For minor modifications including a new instrument (PPMX), a subset of validated foods are required to be analyzed. As such, beef trim and frozen finely textured beef will be analyzed by

both the PPMX sample preparation method.

3.2.1 Pre-screen foods for natural contamination with E . coli O157:H7. Perform total

Formatted: Outline numbered + Level: 3 + Numbering Style: 1, 2, 3, … + Start at: 1 + Alignment: Left + Aligned at: 1" + Indent at: 1.5"

aerobic plate count. Report aerobic counts in study.

3.2.2 To prepare artificially contaminated matrix, inoculate primary samples with E . coli O157:H7 so that on the day of initiation of analysis there is a level such that fractionally positive results, 5–15 positives per 20 replicates, are obtained

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(typically 0.2–2 cfu/test portion, but this may vary).

3.2.3 Use a liquid inoculum for fresh raw beef trim , and finely trimmed beef (FTB) and

fresh vegetables .

3.2.4 Add the appropriate amount of inoculum to the food batch such that the low level yields approximately 0.2–2 cfu/25 g and the high level yields approximately 2–10

cfu/25 g. Mix well.

3.2.5 Interpreting method comparison data can sometimes be problematic due to the homogeneity of samples. It is highly recommended that the lab use extreme care in the inoculation and preparation of samples to achieve as close as possible a 3.2.6 Allow microorganisms to stabilize in the food environment for 48–72 h at 4 ° C. Allow FTB to stabilize in the food environment for minimum 2 weeks at -20 ° C. 3.2.7 For beef trim and FTB , distribute the appropriate number of 25 g test portions for each level of each matrix into two filtered stomacher bags for GDS O157 method . To one set of sample bags of the GDS O157 portions, add 350 g of the appropriate uninoculated material. The other set of sample bags will remain as 25 g samples. To each of the MLG reference method test portions, add 300 g of homogeneous distribution of microorganisms within the food batch.

the appropriate uninoculated material. Mix all test portions well.

For green onions , distribute the appropriate number of 25 g test portions

3.2.73.2.8

Formatted: Outline numbered + Level: 3 + Numbering Style: 1, 2, 3, … + Start at: 1 + Alignment: Left + Aligned at: 1" + Indent at: 1.5"

for each level of each matrix into two filtered stomacher bags.

3.2.83.2.9

Perform candidate method, reference method, and MPN analyses

beginning on the same day.

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