Microbial Detection in Food Safety: Plate Count Method vs. Flow Cytometry
News 18 8 月, 2025
Food safety relies heavily on microbial detection, which plays a critical role in assessing contamination levels, identifying hazards, and ensuring compliance with testing requirements. Selecting the right detection method depends on the type of microorganism, the food matrix, and the goals of the analysis.
Among various approaches—including traditional culture methods, immunological assays, molecular biology, and metabolic techniques—two common methods are the plate count method and flow cytometry.
1. Plate Count Method
The plate count method is one of the most widely used microbiological detection techniques. Common culture media include:
- Nutrient agar: for bacterial cultivation. Requires sterilization at 125°C for 15 minutes.
- Gause’s Medium No. 1: for actinomycete cultivation. Prepared with starch slurry, heated, and sterilized.
- Martin Agar: for fungal isolation. Supplemented with streptomycin solution before use to inhibit bacterial growth.
While widely adopted, the plate count method has limitations: it is time-consuming, cannot differentiate between live and dead cells, and fails to detect microorganisms in a viable but non-culturable (VBNC) state. This limitation has led researchers to explore more advanced methods such as flow cytometry.
2. Flow Cytometry in Microbial Detection
Flow cytometry has become a powerful tool for microbial research and food safety testing. Because microorganisms are small and difficult to distinguish by light scattering alone, flow cytometry relies on fluorescent dyes to identify target cells.
How Flow Cytometry Works
Flow cytometers typically consist of three key systems:
- Fluidics system (for cell transport),
- Optical system (lasers and detectors),
- Data acquisition and analysis system.
Fluorescent dyes commonly used include:
- Nucleic acid-binding dyes such as PI and 7-AAD,
- Protein-labeling dyes such as FITC, PE, and Cy5.
Multi-laser systems (e.g., 405nm, 488nm, 633nm) allow multi-channel fluorescence analysis, improving detection sensitivity while reducing autofluorescence interference.
Example: 7-AAD Detection Method
7-AAD (7-aminoactinomycin D) is a nucleic acid-binding dye that indicates cell death and apoptosis:
- Strong signal → dead cells
- Weak signal → apoptotic cells
- No signal → viable cells
Key steps include preparing a DMSO stock solution, staining cells at a working concentration of 0.5–5 µM, incubating for 15–60 minutes, and analyzing under flow cytometry at Ex/Em = 545/650 nm.
Conclusion
The plate count method remains a reliable, traditional approach for microbial enumeration in food safety testing. However, flow cytometry provides higher sensitivity, faster results, and the ability to detect VBNC cells, making it a valuable complement in modern food microbiology. By combining both methods, laboratories can achieve more comprehensive microbial analysis and ensure stronger safeguards for food safety.