Minimizing the Risk of Contamination and False Results in Bioburden Testing

Reliable microbial test results are pivotal for quality control laboratories. False positives resulting from secondary contamination make root-cause investigations necessary that lose time and cost resources, while false negative results can delay the recognition of a contamination event and thus compound the loss of productivity or, worse, lead to compromised pharmaceuticals being released to market. Bioburden testing, which ascertains that microbial contamination levels remain below set limits along the manufacturing chain, from process water to raw materials and in-process samples, can be somewhat prone to false results if performed in the traditional setup of a manifold, an external vacuum pump, filtration funnels and separate membrane filters. However, integrated and cleverly designed bioburden testing solutions help to minimize the risk.

Several smaller risks that can add up

The main contamination risk of using a traditional setup stems from the operator’s need to perform several manual steps: taking a membrane filter from a dispenser with a sterile forceps, placing it correctly onto the manifold filtration head, removing it after filtration and laying it onto the agar surface of a Petri dish the right way up for subsequent incubation without leaving folds or bubbles that would falsify the result, all the while avoiding secondary contamination. Performing all these steps aseptically according to regulations requires advanced skills and experience. There are bioburden testing solutions that avoid manual handling of the membrane with a forceps, but it is important to be sure that the alternative transfer procedure does not risk the membrane being damaged or torn if, for example, a screwing-on or twisting movement is required.

Certain properties of the testing equipment can add to the contamination risks, for example filtration units without a lid to protect the sample during filtration or the absence in the filtration head of a check valve that prevents cross-contamination of the membrane from backflow. Hardware and accessories that are difficult to decontaminate or Petri dishes that cannot be locked for safe transportation are further potential contamination concerns. Other characteristics of a bioburden testing setup can make enumeration less reliable. Filtering the correct sample volume can be challenging if the level indicators on the funnel are difficult to see from all sides or if the funnel’s design allows unfiltered sample to remain inside after filtration. A possible issue with the traditional workflow is that if the membrane filter is not perfectly placed on the filtration head, sample can by-pass it. None of these setup-related criteria will probably increase the occurrence of false results drastically, but the risks do add up. An operator has to get a sequence of many little things right, every time. Less potential for mistakes can give peace of mind and reduce the need for operator training.

Reduced contamination risk, better consistency

To minimize the secondary contamination risk, the filtration units for the Milliflex Oasis® bioburden testing system were designed to follow an innovative touch-free membrane concept. The membrane filter is fully integrated into the filtration unit and uniquely sealed along the unit’s base to ensure that only the liquid sample and the agar surface ever come into contact with it. Immediately after filtration, when the lid is closed, the pressure within the funnel increases, causing the membrane to bulge outward slightly, taking on a convex shape. This unique mechanism has two advantages: it demonstrates the integrity of the membrane and ensures that the initial contact point of the membrane with the agar’s surface is the middle, paving the way for full and even contact toward all sides and avoiding folds or bubbles under the membrane.

To find out how much difference a bioburden testing setup can make, we performed a study that compared the contamination rates when using a conventional filtration manifold system and, in parallel, the Milliflex Oasis® system. For each testing setup, two skilled and experienced operators in different laboratories independently performed bioburden testing of 50 samples of 100 mL Type 2 sterile water. This was done in non-controlled laboratory environments to simulate a worst-case scenario. Plate contamination rates of 14% (operator 1) and 8% (operator 2) were observed with the conventional manifold filtration system, while neither operator recorded any contamination after using the Milliflex Oasis® system. In addition to the significant differences in secondary contamination rates between the systems used, these data also indicate that with the conventional setup, test results can vary considerably depending on the operator and/or the testing environment, differences that a risk-minimizing system can vastly reduce or even eliminate (contact us for the full application note).

Faster and easier access to reliable data

Beyond its lower risks of secondary contamination, false negatives and inconsistencies between operators, an advanced bioburden testing solution should be able to automatically and digitally capture instrument data and consumables’ information from barcode labels, with no need for any manual record-keeping. This can speed up trending analyses and facilitate the availability of test records at audits while ensuring data integrity and traceability of the entire bioburden testing workflow to support regulatory compliance.

Author Details

Adrien Venchiarutti, Product & Portfolio Manager – filtration devices, Bioburden for pharmaceutical application, MilliporeSigma

Martin Miceli, Regional Commercial Applications Lead Expert, LATAM, MilliporeSigma

Publication Details

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