Micro December 2018

aliquot is plated onto the plate. The plates can be incubated at multiple temperatures (30 ± 1 o C, 1 32 ± 1 o C, 35 ± 1 o C, 37 ± 1 o C or 42 ± 1 o C) with enumeration occurring in as little as 18 hours 2 The 3M Petrifilm Rapid E. coli /Coliform Count Plate was validated according to AOAC 3 Validation Guidelines [2] following the AOAC Official Methods of Analysis (OMA) process. 4 The objective of these studies was to demonstrate that the candidate method accurately 5 enumerated E. coli and coliform in a broad range of foods and select environmental surfaces as 6 claimed by the manufacturer and that no difference in repeatability was observed between the 7 candidate method and the reference methods. For the pre-collaborative studies, thirty-three (33) 8 matrices were evaluated. The following matrices were evaluated with Butterfield’s Phosphate 9 Buffered Diluent (BPBD) only: Pasteurized whole milk, butter, non-fat dry milk, raw ground 10 pork, lamb chop, raw ground chicken, chicken carcass rinsate, shell eggs, liquid egg whites, 11 powdered egg whites, sprouts, cranberries, infant formula with probiotics, infant formula without 12 probiotics, infant rice cereal without probiotics, dry dog kibble, dry cat food, flour and chocolate 13 chip cookie dough. The following matrices were evaluated with BPBD and peptone salt solution 14 (PSS): raw ground beef (73% lean), raw frozen chicken wings, raw milk, whole liquid egg, tuna 15 sushi, smoked salmon, bunched spinach, pasteurized carrot juice, ready-made sandwiches, raw 16 vegetable salad with dressing, chicken feed, soybean meal, stainless steel environmental sponges 17 and sealed concrete environmental sponges. Additional pre-collaborative parameters (inclusivity 18 and exclusivity testing) satisfied the requirements for OMA approval. 19 The purpose of this collaborative study was to compare the 3M Petrifilm Rapid E. 20 coli /Coliform Count Plate to the FDA BAM Chapter 4: Enumeration of Escherichia coli and the 21 Coliform Bacteria [3] , ISO 4382: 2006 Microbiology of food and animal feeding stuffs – 22 Horizontal method for the enumeration of coliforms – Colony-count technique [4] and ISO 23 16649-2:2001 Microbiology of food and animal feeding stuffs – Horizontal method for the 24 enumeration of β-glucuronidase-positive Escherichia coli – Part 2: Colony count technique.at 44 25 °C using 5-bromo-4-chloro-3-indolyl β-D-glucuronide [5] reference methods for the 26 enumeration of coliform and E. coli in dry pet food. 31 32 One matrix, dry dog kibble, was evaluated in this study. The matrix was obtained from a local 33 retailer and screened for the presence of naturally occurring E. coli and coliforms by the FDA 34 BAM and ISO reference methods. No natural contamination was observed so four separate levels 35 of contamination were targeted for the evaluation: uninoculated, 0 colony forming unit (CFU)/g; 36 low, 10-100 CFU/g; medium, 100-1,000 CFU/g; high 1,000-10,000 CFU/g. To obtain the 37 required contamination levels, bulk lots of the matrix were artificially contaminated with a 38 lyophilized culture of Escherichia coli [Q Laboratories (QL) isolate 11007-8 (origin – beef 39 hide)] and Klebsiella pneumonia [Q Laboratories (QL) isolate 11007-7 (origin – raw 40 hamburger)]at each target contamination level. Two replicate samples from each of the four 41 contamination levels were analyzed by both the candidate and reference methods in a paired 42 study design. 43 A detailed collaborative study packet outlining all necessary information related to the study 44 including media preparation, test portion preparation and documentation of results was sent to 45 each collaborating laboratory prior to the initiation of the study. 27 28 29 30 Collaborative Study Study Design

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Preparation of the Inocula and Test Portions

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