Somethin’ Buggin’ Ya? Get the Basics of Bioburden Testing

Ensuring product safety is a top priority of pharmaceutical and medical device industries. One crucial aspect of this process is bioburden testing, which involves assessing for microbial contamination throughout the entire manufacturing process, from raw materials to the final packaging. In this blog, we will go over the basics of bioburden testing, including the regulations involved, common methods and reliable testing solutions. 
  

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What is bioburden testing?

Bioburden testing is the quality control process used to detect and quantify microorganisms like bacteria, fungi, and mold. Microbial contamination poses a major safety risk for medicinal products, particularly those that are administered to patients by injection or other invasive routes. Bioburden testing is also a required pre-sterilization step for ensuring effective sterilization practices for sterile medical devices, such as stents and transplants.

There are several sources of contamination in a manufacturing facility. One source is raw materials. Active ingredients, excipients, and other components used in pharmaceutical formulations can carry microbial contaminants. Another big source is the facility water system, which makes up the greatest number of testing samples. Bioburden testing helps to prevent the risk of infection, maintain patient safety, and comply with regulatory requirements.

Regulatory requirements

Regulatory bodies, such as the United States Pharmacopeia (USP) and the European Pharmacopoeia (EP), have established guidelines for bioburden testing. Pharmaceutical and medical device manufacturers closely follow these regulations to maintain compliance and show that their products meet safety and quality standards.  

In addition to USP and EP guidelines, the International Organization for Standardization (ISO) has their own guidelines for bioburden testing in the pharmaceutical industry. For example, ISO 11737 outlines various aspects of bioburden testing for medical devices, including sample preparation, enumeration (counting) methods, and data interpretation for microbiological protocols. 

What is tested for contamination?  

Microbial Limits Testing is performed on non-sterile final products as well as the sourced raw materials to check if there are any “high risk” contaminants. Anything that comes into contact with the product is also tested: the packaging (before and after sterilization), all equipment used (mixing vessels, filling machines, filtration systems), cleanrooms, and water systems. 

Environmental monitoring is another integral part of maintaining a cleanroom, but it cannot be directly correlated to bioburden testing. However, it can be used to pinpoint where potential challenges may come up in the cleanroom and facility water. For example, having return air right behind a point-of-use port on a water system increases the risk of contamination. To perform environmental monitoring, samples from air, surfaces, and personnel within manufacturing areas are collected and tested to evaluate the microbial load and identify potential sources of contamination.
 

Bioburden testing methods 

A typical microbial testing workflow has two steps: a sample preparation step, and a colony growth and enumeration step. It’s critical that the sampling process and testing equipment themselves are not a source of contamination, which can lead to false-positive results. Sample preparation varies depending on the sample type and may include a filtration step. Next, the sample is transferred to a growth medium, where colonies can grow during an incubation period. Colonies are then counted and reported as colony-forming units (CFUs) per unit volume. 

There are two common methods used for bioburden testing:

• In the membrane filtration method, the sample is first filtered through a porous membrane to capture microorganisms larger than the pore size. The membrane is then transferred to a culture medium for growth. This method is ideal for filterable samples, such as water, liquid raw materials, and soluble products.
• The direct plate method is ideal for samples that can’t be filtered since it does not have a filtration step. A small volume of sample is added directly to a sterile Petri dish and topped with a molten agar medium (pour plate method), which helps to evenly distribute the sample as the agar solidifies. For testing low-bioburden samples, such as finished products, the sample is added directly to solid culture medium (spread plate method), without prior filtration or dilution. 

Reliable solutions for bioburden testing

Sartorius offers a comprehensive portfolio of solutions for microbiological quality control to help pharmaceutical and medical device manufacturing companies ensure both safety and compliance. For workflows using the membrane filtration method, you can use the unique Microsart^® @filter and @media system to safely transfer the membrane to the agar plate, without forceps. 

Read our brochure to learn more about the forceps-free Microsart^® system, rapid microbial testing kits, microbial air monitoring, and more.