Sterility Testing

Tribute to Dr. Scott Sutton; Review of Bioburden Contamination Control

Scott Sutton, PhD, was a well-respected and influential thought leader in the microbiology industry. He was a consultant and trainer in CGMP, investigations, environmental monitoring, and contamination control for pharmaceutical companies for over 30 years. He gave many presentations on these topics, and received multiple awards for his publications in microbiology journals and industry trade publications. For the past 22 years, Dr. Sutton served on the United States Pharmacopeia committee on Microbiology, serving as Vice-Chair from 2000 through 2010.

Dr. Sutton passed away on October 19, 2015. Shortly before his passing, Dr. Sutton published an article regarding the process of controlling bioburden contamination in a manufacturing facility. In memory of this great contributor to the microbiological and pharmaceutical industries, we have highlighted a few key points from this recent article. To read the full article by Dr. Sutton, please click here.

Bioburden contamination is an aspect of product manufacturing that must be considered for all medical devices and pharmaceuticals. Processes to attempt to control the contamination through validations and monitoring in each phase of production should be in place to ensure the bioburden contamination remain at an appropriate level. Maintaining control of the bioburden is far too complex for a single individual or even department to accomplish by themselves, so training and adherence to these processes is vital in ensuring any bioburden contamination stays at a manageable level.

Building Design & Control: Bioburden control in a facility should optimally begin with the design and construction of the building. Areas in a facility that are able to be tightly controlled should be surrounded by areas that are not as easily controlled. An important part of this design is the placement of air filters to ensure the pressure differential between areas allows the aseptic air to be pushed out. An argument can be made that the placement of filters in a terminal location allows for better air cleanliness, however, the ease of monitoring and maintenance should also be considered when placing filters. Facilities should also be designed to prevent personnel and materials from using the same paths to minimize cross-contamination. This type of building design works best when airlocks and pass-through chambers are put in place, as they help maintain bioburden barriers.

Water Systems: The water system of a facility also contributes to the control of bioburden contamination in a building. The properties of water make it an easy avenue for microbial contamination. Because water is often used as a raw material and a utility, frequent maintenance and monitoring are necessary to contain the bioburden resulting from the use of water. The last design element Dr. Sutton discusses is the location of the product when it will be at its most vulnerable point in the manufacturing process. Protection of the environment around the product at this point by an isolator or other environmental controls aids in maintaining control of the bioburden.

Equipment: Once the design of the facility is in place, the next factor to analyze is the equipment being used. In addition to the tasks the equipment is required to perform, the ability to clean and sanitize the equipment should also be considered. Choosing equipment and placing it in locations that allow for easy cleaning and sanitation aids in the exclusion of microorganisms from coming in contact with the product. Fill lines and equipment should also be organized in a way that will not allow for mix-ups or cross contamination between filled products and raw materials. One way to minimize contamination is to eliminate the human factor, and utilize equipment to fill the product.

Cleaning Processes: The sporicides and sanitizers that are used in bioburden control processes need to be tested to show their efficacy against the microorganisms in a facility; generally, this is a four-step process. The first step is a suspension test. This test analyzes the effectiveness of a sanitizer against indicator organisms as well as other organisms found in a facility. This test aids in selecting the best sanitizer for your product and also determines the most resistant microorganism. The second step is a coupon study, performed on materials present in the facility. This study evaluates the effectiveness of the chosen sanitizer against the organisms found in the suspension test. The third step is a “mock” sanitation study to provide real-world analysis of the effectiveness of the sanitizer. The last step of testing the sanitizer is ongoing environmental monitoring. This is usually done by the annual trending of the environmental monitoring to show the bioburden is being adequately controlled.

Personnel: The main source of bioburden contamination during manufacturing process comes from the personnel involved. It is estimated that an individual at complete rest sheds about 10,000 particles per cubic meter. Any movement or activity increases this number exponentially. Because of this, it is important to be careful in selecting gown material and also gowning methods. Simulated trainings, proficiency testing, and monitoring of the operators and their involvement in the manufacturing process are vital to make sure human contamination of the product is limited. Use automation in manufacturing to avoid the chance of mix-ups causing cross-contamination and limit the need for human intervention. To assist in monitoring the bioburden in these processes, bioburden testing should be performed on all material coming into a facility, and checked against existing bioburden acceptance criteria prior to use.

Process Monitoring: Monitoring activities and processes to control bioburden are indirect, so it is important to partner with a reputable testing facility that is knowledgeable on current industry standards in creating and carrying out these procedures. USP has recently released a chapter to help break down laboratory operations into a series of systems, that when paired with other USP chapters are useful in determining the best practices for a facility.

Thank you, Dr. Scott Sutton, for your contribution to the microbiology community.


Need Additional Guidance? Nelson Labs employs many scientists who actively participate in the creation and modification of industry standards who can help interpret the standards and apply them to specific products and facilities.


What You’ll Learn by Attending the MD&M West Nelson Laboratories Classroom on Radiation Sterilization Validation Overview

Martell Winters, Senior ScientistRadiation-sterilization

Martell Winters will present an overview on radiation sterilization at the 2014 MD&M West Conference. Martell is a Senior Scientist at Nelson Laboratories in Salt Lake City, Utah. His presentation will include:

  • Bioburden Testing: How it is performed and what constitutes a good bioburden count
  • Sterility Testing: How it is performed and how to avoid sterility test failures
  • Sterility Suitability Testing (also called B/F): How it is performed and how it relates to sterility testing
  • Radiation Validation: Review of applicable methods and standards
  • Case Studies: Review bioburden and sterility test data to understand approaches to a successful radiation sterilization validation

Take Away:

  • Attendees will learn how to evaluate bioburden data for establishing and monitoring radiation sterilization processes
  • Attendees will be educated as to how method suitability testing can help them receive the best sterility test results the first time around
  • Attendees will gain an understanding of what typically causes sterility test failures and how to avoid them


Martell will present for approximately one hour at the Nelson Labs classroom in 208AB on February 12, 2014 at 1:00 PM.

Register at

Nelson Laboratories website:

Increase Efficiency by Combining Bioburden and Tests of Sterility

By Sean Shepherd, Sr. Study Director, Bioburden, BS, SM/RM(NRCM)Bioburden-testing

When it comes to radiation sterilization validation, there is a perception that the bioburden and sterility testing need to be conducted under separate submissions, with results from both then used to compile a statement report by the medical device manufacturer. Nelson Laboratories suggests it is more cost effective and a better use of time to have both tests prepared as a single report at the same time and same location.

As a result, Nelson Laboratories provides a coordination service of the initial bioburden and sterilization validations along with a full validation report. The initial validation is then used as a reference for on-going quarterly dose audits.

The main advantage is that one report covers all areas of the ISO – AAMI 11137-2 standard requirements. Using this combo approach is a much more thorough and economical way to meet the standard.

The bioburden determination provides information on microbial levels of your device before it is sterilized. The test of sterility provides validation of a selected sterilization dose to achieve a 10-6 sterility assurance level for a medical device.

Nelson Laboratories has staff and resources completely devoted to providing the combined service. The package combines four tests into one report and also includes gram stain of the most prominent bioburden organisms, which is important in establishing a baseline if you don’t already have years worth of data.

Using this coordinated service, medical device manufacturers receive all of the results under one report. The report provides bioburden levels and a report of the test of sterility per the guidance outlined in the AAMI/ISO 11137-2 standard. This service is provided for both initial dose substantiation and quarterly dose audit testing. Nelson Laboratories also provides the final report compilation for the manufacturer who generally would have to do it themselves.