AOAC-RI ERP Book MICRO.pdf

CONFIDENTIAL INFORMATION

Page 6 of 17

“confirmation stage” results

were both positive for a particular sample (POD

). The

difference in POD for the two values at each level of inoculation were calculated

(dPOD

) along with its corresponding 95% confidence interval. As noted above, if

the 95% confidence interval of a dPOD

value does not contain zero, then the

difference between the POD

of the candidate method and the POD

of the

reference method at that level of inoculation is statistically significant at the 5%

level.

3.0 RESULTS

The objective of this study was to

validate the 3M™

Molecular Detection Assay

(MDA) for the detection of

E. coli

O157:H7 in three different food matrices. The

inoculum concentration of

E. coli

O157:H7 in each food matrix was determined

from Most Probable Number analysis, along with the 95% confidence intervals, as

shown in Table 1.

All data obtained for the candidate met

hod testing of spinach, ‘screening stage’

and ‘confirmation stage’ (200 g spinach analyzed by the 3M

MDA) is provided in

Table 2. All data obtained for the reference method testing of spinach (200 g

spinach analyzed by the FDA Bam Ch. 4A) is provided in Table 3. The number of

true positives (samples with a positive ‘screening stage’ and a positive

‘confirmation stage’), true negatives (samples with a negative ‘screening stage’

and a negative ‘confirmation stage’), false positive (samples with a positive

‘screening stage’ but a negative ‘confirmation stage’) and false negatives (samples

with a negative ‘screening stage’ but a positive ‘confirmation stage’

) for the

candidate method testing of spinach is provided in Table 4. As described in

Section 2.7, the results presented here were statistically analyzed according to the

POD methods of the 2012 version of the AOAC International Methods Committee

Guidelines for Validation of Microbiological Methods for Food and Environmental

Surfaces document (1). The POD

, POD

, dPOD

, POD

, and dPOD

values calculated at each level of inoculation for the candidate method and the

reference method testing of spinach, and their corresponding 95% confidence

intervals, are provided below in Table 5.

All data ob

tained for the candidate method testing of sprouts, ‘screening stage’

and ‘confirmation stage’ (25 g sprouts analyzed by the 3M

MDA) is provided in

Table 6. All data obtained for the reference method testing of sprouts (25 g sprouts

analyzed by the FDA Bam Ch. 4A) is provided in Table 7. The number of true

positives (samples with a positive ‘screening stage’ and a positive ‘confirmation

stage’), true negatives (samples with a negative ‘screening stage’ and a negative

‘confirmation stage’), false positive (samples with a positive ‘screening stage’ but

a negative ‘confirmation stage’) and false negatives (samples with a negative

‘screening stage’ but a positive ‘confirmation stage’

) for the candidate method

testing of sprouts is provided in Table 8. As described in Section 2.7, the results