Introduction
At Envirocare Laboratory, innovation drives everything we do. As part of our commitment to delivering precise, reliable, and timely microbiological services, we are proud to announce a major advancement: the transition of our Shigella testing from traditional culture-based methods to a quantitative PCR (qPCR) platform.
What is Shigella and Why Does Testing Matter?
Shigella is a highly contagious bacterium responsible for shigellosis, a severe intestinal illness. Even very low doses (as few as 10–100 organisms) can cause infection, with symptoms including diarrhoea, fever, and abdominal cramps.
Outbreaks are often linked to contaminated ready-to-eat (RTE) meals, fresh produce, beverages, or water sources. This makes Shigella detection critical for:
- Food safety and consumer protection
- Public health outbreak prevention
- Compliance with South African and international food safety regulations
Why Choose qPCR for Shigella Detection?
Traditional culture-based methods are reliable but time-consuming (several days) and can be prone to variability in interpretation. By adopting qPCR molecular diagnostics, Envirocare Laboratory now offers:
✅ Faster turnaround times – rapid results to support quicker decision-making
✅ Lower Limit of Detection (LOD) – identification of contamination at very low levels
✅ Higher accuracy – reduced variability and interpretation errors
✅ Fewer false positives – ensuring results you can trust
This molecular-based approach enhances both sensitivity and specificity, giving food producers and exporters greater confidence in compliance testing.
Validation of Our Shigella qPCR Assay: Key Performance Indicators
To ensure accuracy, reproducibility, and sensitivity, Envirocare validated its qPCR assay for Shigella detection according to ISO17025 standards. Here is some insights delivered by three key graphs to illustrate assay performance:
- Amplification Curve (Multiplexing)
- Blue curves: amplification of the Shigella genetic marker, confirming presence of the pathogen.
- Red curves: internal amplification control (IAC), included in every reaction to verify that the PCR process is functioning correctly and free from inhibition.
This dual-channel system ensures true positives are detected while guarding against false negatives due to sample inhibition or reaction failure.
- Melt Curve Analysis
Melt curve analysis evaluates the specificity of amplification products by gradually heating PCR products and detecting their melting temperature (Tm).
- Single, sharp melt peak indicates that only the intended Shigella target was amplified.
- Absence of additional peaks confirms there is no non-specific amplification, such as primer dimers or off-target products.
This ensures that positive results truly reflect Shigella DNA, enhancing both assay specificity and reliability.
- Standard Curve Performance
The standard curve evaluates assay sensitivity, efficiency, and dynamic range using serial dilutions of Shigella DNA:
- Linearity (R² ≥ 0.99) demonstrates consistent detection across a wide range of DNA concentrations.
- Slope between –3.1 and –3.6 reflects an optimal PCR efficiency of 90–110%.
- Low Cq values at high concentrations and proportional increases at lower concentrations confirm that the assay is both sensitive and quantitative.
This means the qPCR assay can accurately detect both high and very low levels of Shigella contamination, which is essential for testing RTE foods where even trace contamination poses risks.
Regulatory Framework
In South Africa, microbiological food testing, including Shigella, is guided by:
- Regulations Governing Microbiological Standards for Foodstuffs and Related Matters (R.962, amended R.607 of 2018) – covering hygiene and microbiological safety of ready-to-eat products.
- International Standards (ISO 21567:2004 & ISO/TS 13136:2012) – methodologies for Shigella detection, increasingly recommending molecular-based approaches like PCR.
Envirocare Laboratory’s adoption of qPCR ensures alignment with local and international regulatory expectations, giving clients confidence in both domestic compliance and global export readiness.
What Envirocare Laboratory Can Do for You
At Envirocare, we support clients across the food, beverage, and agricultural sectors with:
- Advanced pathogen detection, including Shigella, Salmonella, Listeria, and E. coli
- Microbiological compliance testing for ready-to-eat products, meat, water, and fresh produce
- Accredited testing services for high quality services
- Rapid reporting to help companies avoid costly recalls, protect consumers, and meet regulatory compliance
By combining scientific innovation with client-focused service, we help you safeguard your products and maintain consumer trust.
References
- WHO. Shigella – Key Facts. World Health Organization, 2023.
- ISO 21567:2004. Microbiology of food and animal feeding stuffs – Horizontal method for the detection of Shigella spp.
- ISO/TS 13136:2012. Microbiology of food and animal feed – Real-time PCR-based method for the detection of food-borne pathogens.
- South African Government Gazette. Regulations Governing General Hygiene Requirements for Food Premises, the Transport of Food and Related Matters, R.962 of 2012 (as amended by R.607 of 2018)
Contact Envirocare Laboratory
info@envirocarelab.co.za
Tel: +27 18 294 4283
