Practical validation of sensitivity of microbial rapid detection instrument

This question has practical value. The core of the sensitivity verification of themicrobial rapid detection instrumentis to use gradient concentration standard bacterial solution testing, combined with parallel experiments and comparative verification, to quantify the lowest detection limit (LOD) and reliability of the instrument.

Verify core objectives

Clearly define the minimum concentration of microorganisms (such as CFU/mL) that the instrument can stably identify in actual detection scenarios, ensuring that the results meet industry standards (such as the GB4789 series for food and the GB/T5750 series for water quality) or process requirements, and avoiding the risk of missed detections.

Practical verification steps

1. Preparation of standard bacterial solution

-Select target microorganisms (such as Escherichia coli ATCC25922 and Staphylococcus aureus ATCC29213), culture them pure, and dilute them with sterile physiological saline gradient to prepare a series of bacterial solutions with a concentration range of 10 ⁰ -10 ⁴ CFU/mL.

-Set 3 parallel samples for each concentration, while retaining blank control (sterile physiological saline) to avoid contamination interference.

2. Sample pretreatment and testing

-Process the sample according to the instructions of the instrument. For example, take 1mL of liquid sample and inject it directly into the detection module, and take a sample of solid sample (such as food) after homogenization and dilution.

-The same batch of bacterial solution is tested in parallel with both instrument detection and traditional plate counting method (national standard method), and the positive detection results of the instrument (such as fluorescence signal value and color reaction) are recorded along with the actual number of bacterial colonies counted on the plate.

3. Data statistics and determination of minimum detection limit

-Calculate the positive detection rate (number of positive samples/total number of parallel samples) for each concentration gradient, and use the lowest bacterial solution concentration with a detection rate ≥ 95% as the instrument's practical sensitivity (LOD).

-Compare the consistency between the instrument detection results and the tablet counting results, calculate the relative error (≤ 15% is qualified), and eliminate the interference of instrument false positives/false negatives.

4. Sensitivity verification under interference conditions

-Simulate the actual sample matrix (such as milk, drinking water, soil extract), add the same gradient standard bacterial solution, and repeat the above detection steps.

-Verify whether matrix components (such as proteins and impurities) affect instrument sensitivity to ensure stable detection of target microorganisms in complex samples.

Key precautions

-The dilution process of bacterial solution requires strict aseptic operation to avoid cross contamination. After dilution, it should be tested as soon as possible (generally ≤ 30 minutes) to prevent microbial proliferation or death.

-The instrument needs to be preheated to a stable state in advance and calibrated according to requirements (such as fluorescence intensity calibration and optical path calibration) to ensure consistent detection conditions.

-At least 3 independent experiments should be repeated for each concentration gradient to avoid single data errors. After the experiment, the detection module should be cleaned with sterile water to prevent residual contamination.

Result judgment criteria

-The instrument LOD should be ≤ the minimum limit specified by industry standards (such as the limit of pathogenic bacteria in food is usually 10CFU/g), and the detection rate under matrix interference should not significantly decrease (≥ 90%).

-Compared with traditional methods, a positive agreement rate of ≥ 95% and a negative agreement rate of ≥ 98% are required to confirm that the instrument sensitivity meets practical needs.