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Sterility testing of Pharmaceutical Products

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USP 71 – Sterility Testing

Sterility testing is a significant process in industries that deal with the production of sterile goods such as drugs, medical devices and radioactive drugs. The United States Pharmacopeia (USP) Chapter <71> specifies the methods and acceptance criteria for sterility testing, which are designed to ensure that pharmaceutical products are free from viable microorganisms before they are used in patient environments. Manufacturers need to abide by these guidelines to ensure that quality of their products is high and has met the GMP requirements.

Sterility is defined as absence of viable bacteria, viruses, yeasts and fungi from a particular sample. Maintaining sterility is an important factor in ensuring product quality and minimizing risks to a patient’s well-being. Sterile products are products that have been tested for any sign of microbial content and are demonstrated to be free from microbes for use in medical and pharma products.

USP <71> Test Method

At MIS two primary methods for sterility testing are followed: Membrane Filtration and Direct Transfer Sterility Testing. –

Membrane Filtration Method

The membrane filtration method is a standard test method that is used for assessing filterable pharmaceutical products. This method is applicable to products that contain preservatives, bacteriostatic agents and fungistatic agents to inhibit the growth of microorganisms. In this method, the test samples are passed through a 0.45µm membrane filter under aseptic conditions. On completion of the filtration, the membrane filter is inoculated into a culture media* which supports the growth of the microorganisms and is incubated for 14 days. Growth of microbes in the media is analyzed.

*Growth media: Fluid Thioglycollate Medium (FTM) and Soybean Casein Digest Medium (SCDM) are used in this test. These media are used because they facilitate the growth of anaerobic bacteria, aerobic bacteria, and other microbes like fungi and yeast.

Direct Transfer Sterility Testing

Direct Transfer Sterility Testing is recommended for the sterility testing of medical products. The test method involves the transfer of sample products independently into two types of culture media, FTM and SCDM, which facilitates the growth of microorganisms. The cultures are incubated for a period of 14 days with intermittent observations. Growth of microbes in the media is analyzed.

Applications of Sterility Testing

Sterility testing is an important quality control measure which is used in various industries such as medical and pharma industries to ensure that the products used in these sectors are free from viable contaminating microorganisms. This testing is essential for safeguarding public health and maintaining the integrity and safety of products. Key applications of sterility testing include those for:

Pharmaceutical Products


It must be ensured that parenteral medications including intravenous, intramuscular and subcutaneous injections are sterile.

Ophthalmic Solutions

Ophthalmic preparations such as eye drops are required to be sterile to avoid eye infections.


Biological products like vaccines, blood products and other biologics demand stringent sterility testing for their effectiveness.

Medical Devices

Medical devices that are likely to come in direct or indirect contact with sterile body areas are required to undergo sterility testing.

Surgical Instruments

Surgical instruments employed in operations should be free from microbes in order to prevent postoperative infections.

Catheters and Implants

Products such as catheters, pacemakers and artificial joints need to be sterile before being placed inside the body to avoid any infection.

Tissue and Cell Products

Products derived from human or animal tissues and cells such as:

Tissue Grafts

Tissues for bone, skin and organ transplantation have to be sterile to prevent transfer of infections in the body.

Cell Therapies

Products involving live cells, such as stem cell therapies, must be sterile to ensure patient safety.

Nutraceuticals and Parenteral Nutrition

Sterility testing is also important for products meant for nutrition and dietary supplements used for human consumption.

Total Parenteral Nutrition (TPN)

Intravenous feed solutions given to patients should be free from bacterial contamination as patients on intravenous feeding are prone to infections.


Certain high-risk dietary supplements particularly those that are infused intravenously may also need sterility tests prior to use in order to avoid contamination with unwanted microorganisms.

Cosmetics and Personal Care Products

Products for Broken Skin

Cosmetics which are used on damaged skin like wound care products must be sterile to prevent bacterial infection.

Eye Area Products

Products like mascara, eyeliner and other items that come in contact with the eyes have to be sterile to avoid infections.

Biotechnology Products

Biotech products particularly those involving genetic engineering and cell culture require sterility testing.

Recombinant Proteins

Proteins synthesized using genetic engineering which are utilized in treating different diseases should be free from contaminants.

Gene Therapies

Products used in gene therapy techniques must be devoid of any existing impurities that may harm patients receiving these therapies.

Compounded Sterile Preparations

Hospitals and Clinics

CSPs prepared in hospital and clinic pharmacies must be sterile to ensure patient safety during treatment.

USP Chapter 71 – Sterility Testing at Microbe Investigations (MIS)

MIS performs USP <71> sterility testing of pharmaceutical products using both direct transfer and membrane filtration methods. Additionally, in our testing lab, we have the full capacity of doing USP 51 Preservative Challenge test. With extensive experience in research and analysis, our specialists are at the forefront of quality assurance. 

To submit your sample or get a quote on USP 71 tests, contact our experts here.


USP 71, also known as sterility testing, is performed to confirm that sterile products are free of any viable microbial contaminants.

USP <71> test is used for product sterility testing for pharmaceutical, biopharmaceutical, and medical device industries. Products to be tested using USP 71 test includes, pharmaceutical formulations, medical devices, and radiopharmaceuticals.

USP Chapter 71 test takes 1-2 weeks to complete.

We test for USP 71 using the following microbial strains: Pseudomonas aeruginosa (ATCC 15442), Escherichia coli (ATCC 8739), Staphylococcus aureus (ATCC 6538P), Enterococcus hirae (ATCC 10541), Klebsiella pneumoniae (ATCC 4352), MRSA (ATCC 33591), Salmonella enterica ( ATCC 10708), Candida Albicans (MTCC 3017). Additional strains can be added on request.

Microbiological sterility testing can be defined as the testing of pharmaceutical products or medical devices and other materials for the absence of viable microbial contaminants. It is a very important quality control check to ensure the safety of the end product.

Sterility testing is a crucial procedure that helps determine whether or not the product of interest is fit for human use. This is important in order to minimize the presence of disease-causing organisms and enhance the quality and effectiveness of the products.

Membrane filtration method and direct inoculation are the two most common methods used in sterility testing. Membrane filtration involves passing the product through a membrane which is then inoculated in culture media to see if there is any growth of microorganisms. In the direct inoculation method, the product is directly added into the culture media and later incubated to evaluate the growth of microorganisms.

Sterility testing typically takes at least 14 days to complete.

An incubation period of fourteen days is desirable to allow time for the growth of slow-growing microorganisms that may be present in the product. This extended period will help to improve the reliability of the test results.

The direct inoculation method is one of the test methods used in sterility testing. In this method, the required volume of the product itself is directly placed in the culture medium. The inoculated media is next incubated and examined for the presence or absence of microbial growth. This method is normally applicable if products cannot be filtered.

Some of the common media that are used in sterility testing include Fluid Thioglycollate Medium for anaerobic bacteria and Soybean-Casein Digest Medium (Tryptic Soy Broth) for aerobic bacteria and fungi.

The sterility of the culture media is determined by incubating a portion of the culture media for 14 days at a specified temperature. The absence of bacterial growth indicates that the culture media is sterile.

Membrane filter method involves passing the product through a 0.45-micron membrane filter which captures the microorganisms. This filter is then incubated in a culture medium to detect the presence of microorganisms. This method is preferred for products that can be filtered such as aqueous solutions and some oily preparations.

Sterility testing is an important quality control measure that must be adopted by all pharmaceutical manufacturers in order to ensure the safety of drugs and medical devices. It helps in verifying the effectiveness of sterilization processes and eliminating viable microorganisms.

A 0.45-micron filter is used for sterility testing because it can effectively retain bacteria and fungi while allowing the flow of the liquid product. It is a standard pore size that filters out bacteria without compromising the integrity and quality of the product.

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