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Detection challenges of Escherichia coli O157 in raw meat: Diagnostic discordance between VIDAS, qPCR, and
1Kocaeli Food Control Laboratory Directorate, Microbiology Department, Kocaeli, Türkiye.
Abstract:
This study evaluated the occurrence of Escherichia coli O157 and the diagnostic concordance among immunological, molecular, and culture-based methods in raw meat and mixed minced meat products marketed in Kocaeli, Türkiye. A total of 150 samples, including ground beef, kebab, lahmacun (a traditional Turkish flatbread topped with seasoned minced meat), meatball mixtures, and raw poultry, were collected between January and August 2025. Following selective enrichment in modified tryptone soy broth supplemented with novobiocin (mTSB+n) at 37°C for 18-24 h, samples were analyzed using the VIDAS® UP E. coli O157 immunoassay, real-time PCR (qPCR) targeting rfbE, stx1, stx2, and eae genes, and immunomagnetic separation-assisted culture. O157-associated genetic markers were detected by qPCR in 12 samples (8.0%), whereas VIDAS identified seven positives (4.7%), and culture confirmation was achieved in five samples (3.3%) following targeted IMS application. All VIDAS-positive samples were also qPCR-positive; however, several qPCR-positive samples were not detected by VIDAS or confirmed by culture, indicating method-dependent differences in detection outcomes. Importantly, qPCR revealed O157 profiles characterized by the presence of eae in the absence of detectable stx genes at the enrichment level; however, these profiles could not be recovered by culture. These findings demonstrate method-related variation in detection outcomes between screening, molecular, and culture-based approaches and underline the limitations of relying solely on stx-based molecular detection in food safety surveillance. Rather than a prevalence-focused survey, this study evaluates diagnostic performance in complex processed meat matrices, highlighting the need for integrated, multi-layered strategies for accurate interpretation of E. coli O157 occurrence.
Insights
Different methods for detecting Escherichia coli O157 in meat yield varying results. Integrating multiple diagnostic approaches is crucial for accurate food safety assessments of E. coli O157.
Area of Science:
- Food Microbiology
- Diagnostic Science
- Public Health
Background:
- Escherichia coli O157 is a significant foodborne pathogen.
- Accurate detection methods are vital for ensuring meat product safety.
- Variability in diagnostic performance can impact food safety surveillance.
Purpose of the Study:
- To evaluate the occurrence of Escherichia coli O157 in raw and mixed minced meat products.
- To assess the diagnostic concordance between immunological, molecular, and culture-based methods for E. coli O157 detection.
- To investigate method-dependent differences in detecting E. coli O157 in complex food matrices.
Main Methods:
- Analysis of 150 meat samples (ground beef, kebab, lahmacun, meatballs, poultry) using selective enrichment.
- Detection via VIDAS® UP E. coli O157 immunoassay, real-time PCR (qPCR) targeting specific genes (rfbE, stx1, stx2, eae), and immunomagnetic separation (IMS)-assisted culture.
- Comparison of diagnostic outcomes across the employed methods.
Main Results:
- qPCR detected O157 markers in 8.0% of samples, VIDAS in 4.7%, and culture in 3.3%.
- All VIDAS-positive samples were qPCR-positive, but not vice versa, indicating differences in sensitivity.
- qPCR identified E. coli O157 profiles with eae but without stx genes, which were not recoverable by culture.
Conclusions:
- Significant method-related variations exist in detecting E. coli O157 in meat products.
- Relying solely on stx gene detection in molecular methods may underestimate E. coli O157 occurrence.
- Integrated, multi-layered diagnostic strategies are necessary for reliable E. coli O157 food safety surveillance.
