The spread of foodborne pathogens like Salmonella remains a significant global health challenge. These microorganisms cause millions of infections annually, and more than half of the world’s food intoxications are linked to them. Accordingly, timely detection is essential to halt the spread of these bacteria and reduce infection cases. To this end, a new study tested a PCR method that can detect Salmonella in food products in less than 7 hours. Current standard diagnostic methods require 5 or more days, which significantly slows down the recall of contaminated products from the market and directly increases the risk of an epidemic outbreak.
Why Does Salmonella Pose a Serious Threat?
Salmonella predominantly resides in the intestinal tract of animals and reaches humans through the consumption of contaminated food products—meat, eggs, vegetables, milk, and seafood.
Salmonellosis is recognized as the second most common zoonotic disease (an infectious disease transferable from animal to animal, or to human and vice-versa) in the European Union. According to official data from 2023, 77,486 cases were reported, corresponding to an infection rate of 18 per 100,000 inhabitants. The most commonly detected serovars clinically are S. Enteritidis, S. Typhimurium, and monophasic S. Typhimurium.
The infection manifests with the following clinical signs: nausea, abdominal pain, vomiting, and diarrhea. Although the majority of patients fully recover, children under 5 years old, the elderly, and immunocompromised individuals face a high risk of life-threatening complications. Poor hygiene conditions throughout the food chain—from farm to final consumer—contribute to bacterial contamination.
EU regulations (Reg. EC 2073/2005) strictly require zero tolerance for Salmonella in high-risk food products(e.g., minced meat, dairy products, ready-to-eat vegetables, and mollusks). However, the currently operational standard diagnostic methodology (ISO 6579-1:2017) requires a multi-day procedure that includes pre-enrichment, selective growth, plating, and final confirmation.
The Rapid PCR Method
Researchers tested the new method on leafy greens, minced meat, buffalo mozzarella, and mussels. Both low (1–10 CFU/25g) and high (10–100 CFU/25g) contamination levels of S. Typhimurium were used for testing.
Bacterial DNA Extraction: Two inexpensive and fast methods were compared: simple boiling of the sample and the use of the specialized Chelex-100 reagent. Both methods ensure the rapid isolation of bacterial DNA.
Bacterial Proliferation (Enrichment Phase): The researchers checked which culture medium (BPW – Buffered Peptone Water) better accelerated Salmonella growth. They compared a standard medium and a special capsule-enhanced medium.
Temperature Effect: The standard incubation temperature () and a slightly higher, selective temperature () that promotes Salmonella growth were evaluated.
Pre-preparation of the Medium: Researchers significantly accelerated the process by pre-heating the BPW medium overnight at .
Final Test (qPCR): The iQ-Check kit was used for DNA detection, with an analysis duration of only 70 minutes.
To ensure the study’s reliability, all food samples were checked before the experiment began and confirmed to be free of Salmonella.
In the next stage, food samples were combined with the BPW medium to create a favorable environment for bacterial growth. This mixture was incubated, and researchers periodically took samples at intervals from 0 to 20 hours.
A complex statistical analysis (ANOVA, t-tests, and regression analysis) was used to evaluate the obtained data. The analysis was based on Ct (Cycle Threshold) values, which show how many cycles the PCR needed to detect SalmonellaDNA. The lower the Ct value, the higher the amount of bacteria in the sample.
Key Results: Detection in Less Than 7 Hours
The study found that Salmonella DNA extraction by boiling or with Chelex-100 yields results in 4–5 hours. Furthermore, the Ct value (the cycle of DNA detection) decreased proportionally with the growth of Salmonella.
The optimal condition was the standard BPW medium at . Detection time varied across different food products (minced meat, mozzarella, greens) from 4 hours (greens, high level) to 8 hours (mussel, low level).
The final optimized protocol (BPW pre-heated at + Chelex + qPCR) ensured Salmonella detection in minced meat, mozzarella, and mussels at all levels within 4 hours.
The total workflow requires less than 7 hours.
PCR enables the prevention of epidemic outbreaks and the possibility of urgently recalling contaminated products on the same day. The method’s advantages are conditioned by the high degree of automation in laboratories and its cost-effectiveness compared to traditional methods.
Source: Frontiers in Microbiology
