SN/T 4656.5-2016 in English

Interpretation of Standard Technology

Key Operation Points

Sample Preparation: Accurately weigh 25g of sample and add it to 225mL of diluent. Homogenize for 1-2 minutes. For surface testing, use a 15mm x 90mm standard contact slide to collect bacterial samples.

Media Preparation: Tryptone Soy Agar (TSA) should be sterilized at 121°C for 15 minutes. The pH should be maintained within the range of 7.2±0.2.

Calculation Methods

Colony counts should be performed using the double dilution method. When the number of colonies on a plate is between 20 and 200 CFU, calculate according to the formula T=2kn∑×Ad. Where:

• The k value is determined by the sampling method (k=2 for surface sampling, k=1 for other sampling)
• d is the reciprocal of the dilution
• Report results with two significant figures

Implementation Recommendations

1. Laboratories should regularly use GB/T 8170 to perform data rounding verification

2. It is recommended to set up three replicates for each batch of testing, and the coefficient of variation should be ≤15%

3. The testing environment must meet the cleanliness requirements of ISO 14698-1