Don’t Leave Petri Dishes Open Post-Incubation in GMP Microbiology Labs
Remember: Always keep incubated petri dishes sealed — exposure post-incubation risks contamination, miscounts, and data integrity failures.
Why This Matters in GMP
Petri dishes are used for environmental monitoring, water testing, and product bioburden evaluations. Once incubation is complete, the microbial colonies present must be accurately counted and documented. Leaving dishes open post-incubation allows external contamination to settle on the agar surface, resulting in inflated colony counts or masking of true results. It also introduces biosafety hazards and violates microbiological containment protocols.
For example, if settle plates from a Grade B area are left uncovered on the bench after 72-hour incubation, airborne spores may deposit on the surface, creating false positives. This could mislead trend analysis, trigger unnecessary investigations, or lead to misinterpretation of environmental conditions.
Regulatory and Compliance Implications
21 CFR Part 211.113 requires procedures to prevent microbial contamination of drug products. EU GMP Chapter 6 and WHO GMP emphasize proper handling and documentation of microbiological testing materials. Mishandling petri dishes is viewed as a breach in laboratory procedure and microbial control practices.
Auditors check for adherence to microbiological handling protocols, incubation logs, and
Implementation Best Practices
Establish SOPs that require petri dishes to be sealed with parafilm or closed lids immediately after incubation. Store sealed plates in secondary containers until counting and disposal. Count colonies in biosafety cabinets or designated counting areas with limited air movement.
Document all colony count data promptly and assign CFU values before plates are discarded. Train staff on agar plate handling, contamination risks, and incident logging if exposure occurs. Include petri dish handling in lab audits and contamination control reviews.
Regulatory References
– 21 CFR Part 211.113 – Microbial contamination control
– EU GMP Chapter 6 – Microbiological quality control
– WHO TRS 961, Annex 6 – Environmental monitoring and test material handling
– USP – Microbiological Control of Cleanrooms