Tyler P Stephens

Dr. Tyler P Stephens


Research Focus & Metrics

Academic Career Length

4Years (2023-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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16 January 2023 in Foods
Verified
Journal Article
Open access
PDF file
SASavannah F Applegate
Savannah F Applegate
AEApril K. Englishbey
April K. Englishbey
TSTyler P Stephens
Tyler P Stephens
MSMarcos Sanchez
Marcos Sanchez
The United States Department of Agriculture Food Safety and Inspection Service (USDA FSIS) does not maintain a zero-tolerance policy for Salmonella in poultry and poultry products, despite being a known food safety hazard throughout the poultry industry. In 2016, USDA FSIS established performance standards for a 52-week moving window with the maximum acceptable percent positive for comminuted turkey (325 g sample) at 13.5% (7 of 52 samples). Based upon FSIS verification sampling results from one 52-week moving window, the Salmonella prevalence for each poultry establishment in category 1 (below limit), 2 (meeting limit), or 3 (exceeding limit) are published for public viewing. Moreover, many poultry producers continue to have post-intervention samples test positive. Therefore, the use of quantification would be more valuable to determine the efficacy of process control interventions, corrective actions, and final product Log CFU/g of Salmonella to make rapid, within shift, food safety decisions. Therefore, the objectives of these studies are to develop, verify, and validate a rapid and reliable quantification method utilizing RT-PCR to enumerate Salmonella in the poultry industry from flock to final product and to utilize the method in an application study. BAX® System SalQuant® is an application of the BAX® System Real-Time PCR Assay for Salmonella to enumerate low levels of Salmonella with shortened enrichment times. Curve development encompassed inoculating poultry matrix samples at four levels with an ATCC strain of Salmonella, with three biological replicates per inoculation level, and five technical replicates being run on the BAX® System for various timepoints, gathering the data, and creating a linear-fit equation. A linear-fit equation was provided for each timepoint. The ideal timepoint, based on the statistical parameters surrounding the equation (R2 > 0.80, Log RMSE < 0.60, and enumerable range 0.00 to 4.00 Log CFU/mL (g)) that most accurately estimate Salmonella compared to most probable number (MPN), was chosen to be utilized for further studies.

22 December 2023 in Foods
Verified
Journal Article
Open access
PDF file
ABAaron R. Bodie
Aaron R. Bodie
Dana K DittoeDana K Dittoe
Dana K Dittoe
SASavannah F Applegate
Savannah F Applegate
TSTyler P Stephens
Tyler P Stephens
SRSteven Ricke
Steven Ricke
Poultry is the primary reservoir of Campylobacter, a leading cause of gastroenteritis in the United States. Currently, the selective plating methodology using selective agars, Campy Cefex and Modified Charcoal Cefoperazone Deoxycholate agar, is preferentially used for the quantification of Campylobacter spp. among poultry products. Due to the specific nature of Campylobacter, this methodology is not sensitive, which can lead to skewed detection and quantification results. Therefore, Campylobacter detection and quantification methods are urgently needed. The objective was to develop a shortened enrichment-based quantification method for Campylobacter (CampyQuant™) in post-chill poultry rinsates using the BAX® System Real-Time PCR assay for Campylobacter. The specificity and sensitivity for the detection of C. jejuni, C. coli, and C. lari in pure culture were determined. The BAX® System Real-Time PCR assay consistently detected and identified each species 100% of the time with an enumeration range of 4.00 to 9.00 Log10 CFU/mL. Enrichment time parameters for low-level concentrations (0.00, 1.00, and 2.00 Log10 CFU/mL) of Campylobacter using the BAX® System Real-Time PCR assay were elucidated. It was determined that an enrichment time of 20 h was needed to detect at least 1.00 Log10 CFU/mL of Campylobacter spp. Using the BAX® System Real-Time PCR assay for Campylobacter. As a result, time of detection, detection limits, and enrichment parameters were used to develop the CampyQuant™ linear standard curve using the detected samples from the BAX® System Real-Time PCR assay to quantify the levels in post-chill poultry rinsates. A linear fit equation was generated for each Campylobacter species using the cycle threshold from the BAX® System Real-Time PCR assay to estimate a pre-enrichment of 1.00 to 4.00 Log10 CFU/mL of rinsates detected. The statistical analyses of each equation yielded an R2 of 0.93, 0.76, and 0.94 with a Log10 RMSE of 0.64, 1.09, and 0.81 from C. jejuni, C. coli, and C. lari, respectively. The study suggests that the BAX® System Real-Time PCR assay for Campylobacter is a more rapid, accurate, and efficient alternative method for Campylobacter enumeration.

8 February 2025 in Pathogens
Verified
Journal Article
Open access
PDF file
EOElena George Olson
Elena George Olson
ABAaron R. Bodie
Aaron R. Bodie
HTHaley A. Tarcin
Haley A. Tarcin
PRPeter Marius M Rubinelli
Peter Marius M Rubinelli
SASavannah F Applegate
Savannah F Applegate
SRSteven Ricke
Steven Ricke
The accurate quantification of Campylobacter jejuni in poultry samples is critical for ensuring food safety and compliance with regulatory standards. This study evaluated the performance of three enrichment media—Mueller–Hinton Broth (MHB), Bolton’s Blood-Free Broth 2x (BFBB2x), and Buffered Peptone Water (BPW)—in supporting C. jejuni detection and quantification using the BAX® Q7-RT PCR system and traditional plate count methods. Results demonstrated high reliability across all media types, with BFBB2x and MHB showing the strongest correlations (R2 = 0.99) for the BAX® system. BFBB2x exhibited the lowest RMSE (0.13), while MHB balanced precision (RMSE = 0.4) with sensitivity. For plate counts, MHB and BPW achieved the highest correlations (R2 = 0.99) and precision (RMSE = 0.26), with MHB demonstrating the lowest detection limit (2.56 log10 CFU/mL) compared to BFBB2x (2.93 log10 CFU/mL) and BPW (3.31 log10 CFU/mL). The findings underscore MHB’s robustness as an enrichment medium, offering consistent performance across both molecular and culture-based methods. The current study supports MHB as the more effective medium for the reliable and precise quantification of C. jejuni in poultry-associated matrices, highlighting its utility in minimizing contamination risks and enhancing food safety. Future research should explore its applicability in diverse poultry products and production environments.