The contamination is divided into self-contamination of the culture medium and secondary contamination caused by improper unpacking operations. Therefore, laboratory personnel need to make a careful distinction before using the petri dish, and then use it after inspection and confirmation.
Cause Analysis:
1. The medium itself carries bacteria (mainly mold and colonies are usually inside or on the medium).
The manufacturer's production control is not strict, and the microbial load is too large before sterilization;
The gamma ray sterilization dose is low (the mold is more resistant);
Secondary pollution caused by damaged packaging.
2. The problem of bacterial contamination caused by improper use (the probability of bacterial mold is equal, mostly on the surface of the medium or the edge of the agar and plate).
Small packages use the remaining temporary storage (refrigerator or Class A area);
The special case of unpacking the three-layer packaging at one time at the transfer window in the common area;
When unpacking, the movement range is too large, and the dishes are scattered;
In b/c two items, there will be special contamination phenomena, bacteria growing on the edge of the plate, or a special case of growing along the gap between the plate and the medium. (This is usually related to packaging vacuum and airflow sucking)
Treatment measures:
Carefully observe before unpacking, the stained plate is easy to be found before use;
New batches, and low temperature storage are the potential risks of false negative mold results;
Provide necessary training to operators to enhance awareness of aseptic operation.
