In order to determine the total number of colonies, the sample to be tested is usually made into several different dilutions of 65,438+00 times, and then 65,438+0 ml is taken from each dilution and mixed with nutrient agar medium in a sterile Petri dish. After being cultured at a certain temperature for a certain period of time (generally 48 hours), the number of colonies formed in each dish is recorded, and the total number of bacterial colonies contained in each gram (or milliliter) of the original sample is calculated according to the dilution multiple.

The basic operation generally includes: sample dilution-pouring into the plate-culturing for 48 hours-counting report.

The determination methods of the total number of colonies at home and abroad are basically the same, and there is no obvious difference from sample treatment, dilution, plate inversion to counting report except for some specific requirements. For example, some countries have made specific provisions on the flow rate of liquid in straws, the oscillation amplitude, time and times of diluent and the storage time.

See:

GB4789.2-94 "Determination of the Total Number of Colonies in Microbiological Inspection of Food Hygiene in People's Republic of China (PRC)"

SN0 168-92 "Total number of export food colonies in People's Republic of China (PRC) * * * export commodity inspection industry standard"