Bioburden control

Addressing microbial contamination

Bioburden control is of concern for both biomanufacturers and their suppliers. The risk of microbial contamination is inherent in most production scenarios for biologicals. Conditions in the upstream process, with controlled temperature and a nutrient-rich medium, support not only growth of the target cells but also of other biological organisms.

Downstream operations also have their share of challenges. Open containers might be used to transfer product or handle buffers. Raw materials and processing aids that have contact with the product, like chromatography resins and buffer components, are introduced. Transfer of equipment between rooms exposes the process to contamination. Unit operations like chromatography frequently involve a large amount of manual handling, for example during resin slurry preparation and column packing. Success is highly dependent on the skill and experience of personnel; and wherever humans intervene, there is a potential source of bioburden.

Improvements in raw material quality, equipment design, chromatography resin properties, and ways of working minimize the risk of microbial contamination incidents.

Adequate equipment design

The choice of equipment highly impacts contamination risk. Single-use chromatography features systems with disposable flow paths and prepacked chromatography columns that can be discarded after use, reducing risk of cross-contamination between batches or campaigns.

Optimized sanitization methods and resin properties

Establishing efficient sanitization methods for use both proactively and in case of a microbial contamination incident is essential. A Bacillus subtilis spore challenge test shows that 1.0 M NaOH is not sufficient for reduction of spores to below acceptable levels, not even after an extended contact time of 24 h. With peracetic acid (PAA), however, a > 6.2 log reduction of B. subtilis spores was observed already after a 15 min treatment with 30 mM PAA or after a 30 min treatment with 20 mM PAA. Robust chromatography resins that tolerate harsh cleaning and sanitization conditions are a prerequisite for efficient cleaning and sanitization to enhance bioburden control in downstream processes.

Appropriate ways of working

Entrance of bacteria can be prevented by working aseptically. Process automation and integration of unit operation into closed systems omit the need for open handling of process material.

High raw material quality

Raw materials constitute potential sources of microbial contamination. Disposable bags and tubing assemblies and prepacked chromatography columns delivered ready for use and pre-made buffers delivered in closed single-use containers reduce the contamination risks.