April 19, 2017

Bioburden sources you might have missed

By David Westman, Global Product Marketing Manager BioProcess Chromatography Resins at Cytiva

A problem with traditional mAb manufacturing is that there are so many potential entry points for microbial contamination. There are, however, ways to shut the door on contamination.

A complex issue

Monoclonal antibody (mAb) manufacturing is complex. This leads to many potential entry points for microbial contamination. What can you do to minimize the risk to patients—and your reputation?

“Procedures designed to prevent microbial contamination of drug product purported to be sterile are not established, written and followed …” (1). Words like these would send a shiver down the spine of even the most hardened biopharmaceutical production managers. To them, this statement is immediately recognizable as one issued in a warning letter from a regulatory agency like the US Food and Drug Administration (FDA), the European Medical Agency (EMA) or the China Food and Drug Administration (CFDA).

Not following agreed procedures is in direct conflict with current good manufacturing practice (cGMP) regulations, which aim to prevent instances of contamination amongst other things. Companies that receive such a warning would officially be considered deviant from the approved practice and would need to get to the source of the microbial contamination as a matter of urgency.

How do you shut the door on contamination?

The problem with traditional mAb manufacturing is that there are so many potential entry points for microbial contamination. This makes bioburden prevention and control in the production facility extremely important. It also underlines the risk that human error will be the cause of a contamination incident. Historically, many process steps have been performed using open vessels with exposed inlets and outlets and, because we are human, we are prone to making errors.

The risk is most acute in the upstream process, which should not be a surprise. Look at the production process for mAbs. What better place for a bacterial contamination to grow than in a well-aerated, nutrient-loaded cell culture medium? But that is not the only potential source of the problem.

Downstream operations also have their share of risk. Take column packing for example. It has always been a notoriously messy business, with open containers, occasional super-slippery spills of resin and awkward maneuvering of heavy equipment. Success here has also been highly dependent on experienced personnel. And wherever humans intervene, there is a potential source of error. Even the transfer of equipment between rooms by people exposes the process to contamination. Whenever the flow of product from bioreactor to vial can meet contaminated surfaces, gases or liquids, there is a risk. Here is a list of potential bioburden entry points:

1. Addition of nutrients, gases, solutions

2. All interfaces between units in the manufacturing flow

3. Introduction of probes and monitors

4. Changing filters

5. Handling chromatography resins and equipment

6. Movement of equipment into the production environment

7. Maintenance, cleaning, and sanitization activities

8. Buffer preparation

9. All personnel movement into the production environment

10. All airflows into the production environment

Standard operating procedures (SOPs) and appropriate monitoring should be in place to control the activities associated with all these routes.

To make matters worse, the first critical capture step in mAb processing combines the highest concentration of cell culture nutrients with a protein A resin that does not respond well to harsh cleaning. This certainly increases the risk of bioburden.

Open minds use closed systems

The use of single-use systems has in many ways simplified things and can solve most contamination issues at smaller scales. Cell culture can be performed in bags, and upstream and downstream operations can be done in the same ‘ballroom’-style facility. Both options provide low bioburden risks and greater flexibility. Such an approach can also be adapted as products, scales of production, and unit operations change over time.

Automation and preconfigured methods have had a major positive impact. Today, there are automated solutions addressing many parts of the workflow. These make the whole process much less ‘hands-on’, more reproducible, and, for the most part, a closed operation.


The future will be designed

Continuous bioprocessing is an area that potentially allows the use of closed systems. A move in this direction is encouraged by the biopharmaceutical industry for reasons of process economy, and by regulatory agencies for reasons of product quality (2).

However, true continuous bioprocessing remains challenging and unattractive for companies where time-to-market and multi-product flexibility are more important keys to success than the cost of goods. Continuous bioprocessing presents both an opportunity and a problem. The opportunity is that as systems become more closed and more automated, they reduce the risk of bioburden. The problem is that continuous operations are online for days, weeks, or months instead of hours. The time for bioburden to flourish increases—so the operation must consider raising the bar even higher to prevent contamination. This is a hurdle that might prove too large to overcome for existing processes and facilities.

From the standpoint of bioburden control the good news is that simplifications such as connecting downstream unit operations "straight-through" would certainly be a plus. Also, an apparently simple task such as hands-free buffer preparation in flexible quantities can benefit manufacturers, regardless of market niche and business model. Creating buffers in-line at point of use is available here and now, and clearly mitigates microbial contamination risks due to manual operations (3).

Controlling bioburden — a multifaceted challenge

What we see evolving in biologics manufacturing strongly relates to bioburden control:

  • Closed systems are becoming available for previously risky, open activities.
  • Single-use systems are becoming established for smaller scale operations, where flexibility is a requirement and when rapid changeovers are important.
  • Hands-on operations are being automated—complicated facilities with numerous air and people flow challenges can be simplified.

In future articles, we will look at how suppliers and biopharmaceutical companies can cooperate to reduce the risk of bioburden. If you want to read more, be sure to sign up.

Want to learn more about recent technology developments that can reduce the downstream bioburden challenge? View the on-demand webinar Setting new standards for sanitization of chromatography resins.


1. FDA warning letters: https://www.accessdata.fda.gov/scripts/warningletters/wlFilterBySubject.cfm. Accessed 29 March 2017.

2. Farid, S. et al. Continuous bioprocessing: the real thing this time? MAbs 6, 1357–1361 (2014).