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Published Articles from USDA ARS National Program 108: Food Safety
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Title: Non-stochastic sampling error in quantal analyses for Campylobacter species on poultry products
Authors: Irwin PL, Reed SA, Brewster JD, Nguyen LT, He Y
Journal: Anal Bioanal Chem
Accepted date: 2012 Dec
Interpretive summary: The contamination of foods with pathogenic bacteria (e.g., Campylobacter jejuni or C. coli) can lead to food poisoning epidemics. In order to determine the concentration of Campylobacter bacteria in foods it is necessary to be able to quantify as few as a couple of bacteria per sampled volume or mass because the level of these organisms in foods is presumed to be very low. For this purpose we developed a most probable number (MPN) assay using a DNA identification technique, the polymerase chain reaction, to determine if the target organism grew or not (+ or result). Using this method we found that the cell concentration step was introducing unnecessary error but such error was lessened as the concentration of bacteria dropped below 300 cells per 500g. Thus, such errors should be of little consequence in real samples which have naturally low levels of contamination. Using our method on real samples we were able to quantify 14 to 1226 MPN per 500g of naturally contaminated chicken (skinless chicken pieces) and 18 to 244 MPN per 500g chicken wings, breasts, legs, and thighs (skin on) whereupon about 50% of the 29 total samples tested negative. Four of these samples did have substantially lower Campylobacter levels: 1.24 to 6.11 MPN per 500g. This rsearch provides tools for more accurate quantification of pathogenic bacteria in food.
Publication date: 2013 Mar
Volume: 405
Issue: 7
Pages: 2353-69