Analysis of bacterial contamination in petri dishes
Contaminated bacteria are divided into self-contaminated culture medium and secondary contamination caused by improper unpacking operation. Therefore, laboratory personnel need to make a careful distinction before using the petri dish, and use it after inspection and confirmation.
Cause Analysis:
1. The medium itself carries bacteria (mostly molds and colonies are usually inside or on the surface of the medium).
The manufacturer's production control is not strict, and the microbial load is too large before sterilization;
The sterilization dose of gamma radiation is low (the mold is more tolerant);
Secondary pollution caused by damaged packaging.
2. Bacterial contamination caused by improper use (the probability of bacteria and mold is equal, mostly on the surface of the culture medium or on the edge of the agar and the plate).
Use the remaining temporary storage for small packages (refrigerator or A-level area);
Unpacking A special case of unpacking three-layer packaging at one time in the pass window in the general area;
The movement range is too large when unpacking, and the plates are scattered;
In the two items b/c, there will be special infections, which are special cases where bacteria grow on the edge of the plate, or grow along the gap between the plate and the culture medium. (This is usually related to packaging vacuum and airflow suction)
Treatment measures:
Observe carefully before unpacking, the stained plate is easy to be found before use;
New batches and low-temperature storage will increase the potential risk of false negative results for mold;
Provide necessary training to operators to enhance the awareness of aseptic operation.
