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United States Department of Agriculture

Agricultural Research Service

Title: Enumeration of Salmonella with the Polymerase Chain Reaction Bax System and Simulation Modeling

Author
item Oscar, Thomas

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2003
Publication Date: August 10, 2003
Citation: OSCAR, T.P. ENUMERATION OF SALMONELLA WITH THE POLYMERASE CHAIN REACTION BAX SYSTEM AND SIMULATION MODELING. MEETING ABSTRACT. 2003. pp. 119-120.

Technical Abstract: Concepts of microbial growth kinetics, polymerase chain reaction (PCR) detection of pathogens and simulation modeling were combined to develop a predictive model for initial contamination of chicken with Salmonella. Kinetic data from challenge studies with a single strain of Salmonella Typhimurium and chicken homogenates (25 g:225 ml) were used to build the model. Chicken samples were inoculated with 100 to 106 CFU of S. Typhimurium followed by incubation at 37°C for 24 h. Sub-samples were collected during incubation and tested for S. Typhimurium using the PCR BAX system with a sensitivity of 104 CFU/ml. A detection time score (DTS) based on the widths of the PCR gel bands for the sub-samples was obtained for each inoculum level. Standard curves relating PCR DTS to inoculum level were developed using a two-phase linear model. Uncertainty of the best-fit values for standard curve parameters was modeled using probability distributions and Monte Carlo simulation. A simulation model was designed to predict the distribution of Salmonella contamination among any size sample of chicken that was a multiple of 25, the grams of chicken used to build the model. Type of sterile chicken meat did not affect the shape of the standard curve, whereas microbial competition did. Presence of competing microorganisms suppressed growth and thus, PCR DTS at low but not at high inoculum levels. Simulation results indicated that distribution of Salmonella contamination increases in a non-linear manner, as a function of sample size and thus, linear extrapolation of enumeration results is not appropriate.

Last Modified: 7/28/2014
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