AOAC-RI ERP Book MICRO.pdf

February 20, 2013

presumptive positives compared to the confirmed positive contains zero. Therefore, there was no

significant difference in the results at the 5% level. The number of samples that were confirmed

positive from the 3M Petrifilm SALX System was compared to the number confirmed as positive by the

reference method using probability of detection (POD) and difference in probability (dPODc). The 95%

confidence interval for the dPOD for the 3M Petriflm SALX System confirmed positives compared to

the reference method confirmed positive contains zero. Therefore, there was no significant difference

in the results at the 5% level.

Stainless Steel

All uninoculated control samples of swabs of stainless steel were confirmed negative for

Salmonella

The samples were inoculated with an estimated 841 cells/coupon of

Salmonella enterica

spp. Kahla

(ATCC 17980)based on the plating of the inoculum. The 3M Petrifilm SALX System detected 6

presumptive colonies, all of which confirmed positive after incubation with the 3M Petrifilm SALX

Confirmation Disk. All 6 of the 3M Petrifilm SALX System confirmed samples confirmed positive with

the MLG 4.05 method. There were 7 sponge samples from stainless steel that were determined to be

positive by the FDA BAM Chapter 10 method. When comparing the number of samples determined to

be positive by the 3M method to that of the reference method, there was no statistical difference in

the results obtained (χ

<3.8, p<0.05). The number of samples that were presumptive positive from the

3M Petrifilm SALX System was compared to the number confirmed as positive using probability of

detection (POD) and difference in probability (dPODcp). The 95% confidence interval for the dPOD for

the 3M Petrifilm SALX System presumptive positives compared to the confirmed positive contains

zero. Therefore, there was no significant difference in the results at the 5% level. The number of

samples that were confirmed positive from the 3M Petrifilm SALX System was compared to the

number confirmed as positive by the reference method using probability of detection (POD) and

difference in probability (dPODc). The 95% confidence interval for the dPOD for the candidate method

confirmed positives compared to the reference method confirmed positive contains zero. Therefore,

there was no significant difference in the results at the 5% level.

Conclusions

The 3M Petrifilm Salmonella Express System was evaluated following the AOAC

Performance Tested

Methods

requirements: inclusivity/exclusivity, ruggedness, stability/lot to lot consistency and method

comparison. Nine matrices were tested by both the 3M Petrifilm SALX System and either the

USDA/FSIS-MLG or the FDA-BAM for the detection of

Salmonella

species in food. Overall the assay

was equivalent to the reference methods based on the Chi square test for significant difference and

the Probability of Detection (POD). There were no unexpected results in all of the other PTM

requirements.

The 3M Petrifilm Salmonella Express System is sufficiently rugged to withstand small variations in the

experimental parameters of enrichment incubation time and temperature, plate incubation time and

temperature, disk incubation time and temperature and various plate hydration options. Each

parameter was testing using both the high and low microbial load methods as described in the

Instructions for Use.

The method was considered easy to perform and the package insert was found to be straight forward

and easy to follow. The 3M Petrifilm SALX

System offers a significant savings in time when compared

to the traditional reference methods as confirmed positive results can be obtained in as little as 44

hours for low microbial load matrices and 52 hours for high microbial load matrices. For foods with low

microbial load, the 3M Petrifilm SALX method eliminated the need for transfer of enriched test

portions to secondary enrichments. Overall, the 3MPetriflm Salmonella Express System was found to