SOP for Container Closure Integrity Testing by Microbial Ingress

In short: This example SOP describes a microbial ingress (immersion) challenge test for the container closure integrity (CCI) of sealed vials. Filled vials are immersed in a suspension of a challenge organism, exposed to a vacuum cycle, and then incubated to see whether microorganisms entered. Adapt it to your own quality system and validate it for your container closure system.

Why container closure integrity matters

A sterile product stays sterile only if its container closure system keeps microorganisms out for the whole shelf life. EU GMP Annex 1 (2022) expects the integrity of sealed containers to be demonstrated: glass ampoules, blow-fill-seal units and small containers (100 ml or less) closed by fusion should be 100% integrity tested with validated methods (reduced sampling may be acceptable for fusion-sealed containers over 100 ml where scientifically justified), while containers sealed by other means should be sampled and tested with validated methods on a scientifically justified plan (Annex 1, 8.22–8.23). It also states that visual inspection is not an acceptable integrity test method (8.22), and that vacuum-sealed containers are tested for maintenance of vacuum after an appropriate pre-determined period, before certification/release and during shelf life (8.24).

Microbial ingress is one of several CCI methods. It is a probabilistic method: a “no growth” result shows that no organism entered in that particular test, but it can miss very small leaks, so it is generally used for method development, validation and investigation, often alongside deterministic physical methods such as vacuum decay or helium leak testing. Describe the method’s detection limit in your validation report.

Example SOP

This is an illustrative template. Document numbers, limits and formats marked “XXX” and all values are example in-house criteria; replace them with values supported by your own validation.

1. Purpose

To describe the procedure for testing container closure integrity (CCI) by microbial ingress.

2. Scope

This procedure applies to the Microbiology Department at the site.

3. Responsibility

The Officer/Executive in the Microbiology Department performs the test and records the results as written.

4. Accountability

The Head of Microbiology is accountable for the procedure being followed.

5. Procedure

5.1 General instructions

1. Handle cultures only inside a biosafety cabinet.
2. Wear a mask and sterile gloves while handling cultures.
3. Use a fresh sterile pipette for every transfer.
4. In case of a culture spill, disinfect the area immediately with 70% IPA.
5. After the activity, mop the area with 70% IPA.

5.2 Preparing the challenge culture suspension

1. Take the E. coli working culture slant (weekly working culture) out of the refrigerator 30 minutes before testing, let it reach room conditions, and move it into the biosafety cabinet in the culture handling room.
2. Spread the culture over the whole surface of two pre-incubated 90 mm SCDA plates.
3. Incubate at 30–35 °C for not more than 72 hours.
4. Prepare a suspension giving about 10⁴–10⁵ CFU/ml (example in-house criterion).
5. Wash the growth from the plates into 100 ml of sterile diluent and vortex to mix uniformly.
6. Label this dilution 10^-1. Transfer 10 ml into 90 ml diluent (10^-2) and continue serial dilutions to 10^-6, in duplicate.
7. Plate 1.0 ml of each dilution on two sterile plates and incubate at 30–35 °C for not more than 72 hours.
8. Keep each dilution at 2–8 °C until the plate counts are available.
9. Record results in the current version of the specified format (Format No. XXX).

5.3 Test procedure

1. Visually inspect all vials for sealing defects. (Visual inspection is a screening step only; it is not itself an integrity test.)
2. Send the samples to the Microbiology laboratory. For a media fill, take 50 vials as specified in the media fill protocol (example in-house criterion).
3. Transfer the vials into the culture handling room through the dynamic pass box.
4. Enter the testing area as per SOP No. XXX “Entry and Exit Procedure for Testing Area” and operate the biosafety cabinet as per SOP No. XXX.
5. Pour approximately 2 litres of the E. coli suspension (10⁴–10⁵ CFU/ml) into the leak test apparatus.
6. Positive control: puncture the rubber stopper of one vial with a needle, immerse it with the test vials, disinfect the punctured vial afterwards, and incubate it with the others.
7. Immerse the test vials in the suspension and operate the apparatus as per SOP No. XXX. Apply the vacuum and hold it for the defined time (example in-house criterion: 5 minutes; vacuum level to be defined from your validation, see the note below).
8. Remove the vials, disinfect the outside of each vial with the approved disinfectant and dry them in the biosafety cabinet.
9. Transfer the vials to the incubation room through the dynamic pass box (SOP No. XXX) and incubate at 20–25 °C for not less than 7 days followed by 30–35 °C for not less than 7 days (example in-house criterion).
10. Inspect for turbidity or growth and record in the current sterility test / media fill format (Format No. XXX). Any positive vial is investigated; the positive control should show growth for the test to be valid.

Abbreviations

CCI: container closure integrity. CFU: colony forming unit. SCDA: soyabean casein digest agar. IPA: isopropyl alcohol.

Frequently asked questions

Is a microbial ingress test enough to prove container closure integrity? Not on its own. It is probabilistic, so a pass can occur even when a very small defect exists. Many sites use it to validate the container closure system and pair it with deterministic physical methods for routine testing.

Can visual inspection replace an integrity test? No. Annex 1 (2022) states that visual inspection is not an acceptable integrity test method.

How long must the test records be kept? Records must be kept at least 1 year after the expiry date of the respective product batch (EU GMP Part I Chapter 4 §4.11, or 5 years after QP certification if longer; 21 CFR 211.180(a)), longer if local law or the marketing authorisation requires.

See also: SOP for media fill validation and What is the meaning of sterility test.

References

1. European Commission, EudraLex Volume 4, Annex 1: Manufacture of Sterile Medicinal Products (2022 revision), paragraphs 8.22–8.24.
2. United States Pharmacopeia, General Chapter <1207> Package Integrity Evaluation – Sterile Products (current edition; subscription required, not reviewed in full).
3. EudraLex Volume 4, Part I, Chapter 4: Documentation, §4.11; 21 CFR 211.180(a).