Bioburden Testing

Bioburden testing, is a quality control measurement standard used to assess microbial contamination present on various surfaces, equipment, or products. A common methodology for measuring this is USP <61> ^[1]. This testing is used in industries where maintaining sterile environments and products is important. Bioburden enumeration is key in understanding the levels of microorganisms in each product during the manufacturing process by virtue of screening for aerobic bacteria and fungi, and thus reflecting the quality of the final product. This method does not apply to products or samples that are deemed to be sterile ^[2].

History of Bioburden Testing

Before the establishment of formal standards like USP <61>, microbial contamination often went unnoticed or was inadequately controlled. As the pharmaceutical industry grew and diversified, so did the need for more comprehensive quality control measures. The emergence of antibiotic-resistant strains of bacteria, coupled with increased scrutiny from regulatory authorities heightened the urgency of addressing microbial contamination in pharmaceutical products. In response to these challenges, USP <61> was developed by the United States Pharmacopoeia as a set of standardized guidelines and procedures for bioburden testing ^[1]. These guidelines aimed to provide a systematic approach to assess the microbial load in pharmaceutical raw materials, finished products, and medical devices by counting the microbial load of bacterial colonies in colony-forming units per milliliter (CFU/mL) (see image 1 for visual).

Image 1: A positive control sample of a bioburden test is measured in Colony-forming-units (CFU) per milliliter (mL) of tested solvent.

Importance of Bioburden Testing for Quality Assurance

Microorganisms can find their way into production processes or onto surfaces through a multitude of avenues. The presence of these microorganisms can compromise the safety, efficacy, and quality of products and equipment ^[3]. Bioburden testing plays a pivotal role in ensuring that the microbial load within laboratory products.

USP <61> involves the collection of samples from specific products of interest. These samples are then cultured on nutrient-rich media and incubated under controlled conditions. The growth of microorganisms is closely monitored and quantified. A successful bioburden test will display that the microbial colony count is below the minimal accepted CFU quantity, allowing for appropriate corrective actions when necessary.