1. Purpose

To describe the procedure for monitoring microbiological contamination in controlled areas using the settle plate (passive air sampling) method.

2. Scope

This SOP is applicable to all classified areas (Grade A/B/C/D) in manufacturing and microbiology laboratories where viable airborne microbial monitoring is required.

3. Responsibility

• Microbiologist/Analyst: Place, retrieve, and incubate settle plates, record results.

• QC Supervisor: Review results and ensure compliance with limits.

• QA: Approve records and ensure corrective actions in case of deviations.

4. Materials & Equipment

• Sterile Petri dishes containing Soybean Casein Digest Agar (SCDA)

• Timer/clock

• Permanent marker for labeling

• Incubators (20–25°C and 30–35°C)

• Cleanroom garments/PPE

5. Procedure

5.1 Preparation

1. Prepare sterile SCDA plates (55–90 mm size).

2. Label plates with location, date, time, and analyst initials.

3. Transport plates in sterile, closed containers to the testing area.

5.2 Sampling Procedure

1. Place settle plates at predetermined monitoring points (as per environmental monitoring plan).

2. Keep plates exposed for 4 hours (±10 minutes) in each location.

3. Ensure plates are not disturbed during exposure.

4. After exposure, close the lid and transfer plates back to the microbiology lab in sterile carriers.

5.3 Incubation

1. Incubate plates at 30–35°C for 48–72 hours (bacterial growth).

2. Incubate additional set at 20–25°C for 5–7 days (fungal growth).

3. Observe and count colonies.

5.4 Calculation & Reporting

• Report results as CFU/plate/4 hours.

• Compare against cleanroom classification limits (per EU GMP Annex 1 / ISO 14644 / WHO).

6. Acceptance Criteria (per EU GMP Annex 1, example values)

• Grade A: <1 CFU/plate

• Grade B: 5 CFU/plate

• Grade C: 50 CFU/plate

• Grade D: 100 CFU/plate

(Facility-specific limits should be used based on validation and regulatory requirements.)

7. Precautions

• Avoid talking, sneezing, or unnecessary movement near exposed plates.

• Handle plates aseptically during placement and retrieval.

• Do not reuse plates.

• Ensure environmental monitoring is performed during actual operations.

8. Documentation

• Record location, date, exposure time, incubation details, and colony count in Environmental Monitoring Logbook.

• Record any excursions and notify QA immediately.

9. References

• EU GMP Annex 1

• USP <1116> “Microbiological Control and Monitoring of Aseptic Processing Environments”

• ISO 14644 Cleanroom Standards