Bioburden Test for Medical Device

Bioburden is the population of viable  microorganisms in or on a product. Bioburden test determine the number of these microorganisms present, reported as colony forming units (cfu).  A knowledge of bioburden can be used in a number of situation as a part of ;

         i) Validation and revalidation of sterilization processes

        ii) Routine monitoring for control of manufacturing processes

       iii) Monitoring of raw materials, components or packaging

       iv) Assessment of the efficiency of cleaning processes

        v) An overall environmental monitoring programs

ISO 11737-1 specify requirement and provided guidance for the enumeration and microbial characterization of the population of viable microorganism on medical devices. The ISO 11737-2 document describe detail procedure in conducting bioburden test on medical devices from selection of product samples and appropriate method for bioburden determination to microbial characterization of bioburden.  It also describe the validation of the bioburden method emphasizing on the extraction efficiency (correction factor determination) either by repetitive extraction or inoculation procedures.

1. Selection of product for bioburden test

     Samples of product to be tested should be representative of production batches.  The number of samples required to give a reliable bioburden estimate (BE) will depend on the purpose of the bioburden enumeration.  Generally, for routine bioburden test for QC monitoring requires between 3-10 samples selected at random. For sterilization validation, gamma sterilization require 10 samples from 3 different batches for a total of 30 samples, while for EO sterilization, 10 samples are tested.  For large samples, sample in portion (SIP)  may be use where representative parts of the device are taken in portions and the SIP ratio is calculated and use in the final calculation of average BE.

2. Removal of viable microorganisms.

     Various techniques of dislodging the viable microorganisms from the samples can be used including stomaching, ultrasonication, mechanical shaking, vortex mixing, flushing and even blending if possible. The choices of extracting fluids is also recommended from sterile water to sterilized solution of  surfactants such as polysorbates.

There should be a balance between extracting the microorganisms aggressively without killing the  viable microbes. The efficiency of extracting the microbes from the medical device may be determined as part of the validation protocol in bioburden test. Repetitive recovery or repetitive extraction should be conducted to obtain the correction factor which will be used to compensate for the extraction efficiency. Alternatively if the bioburden count is known or expected to be less than 10 cfu/device, inoculation method should be followed to estimate the extraction efficiency and thus the correction factor. Detail discussion on correction factor determination may be view here.

3. Culturing of extracted microorganisms.

     Once the microorganisms have been extracted into solution, there are a few techniques of culturing the microbes which can be used.  The most common technique is membrane filtration where the solution of microbes is filtered through a sterile filter paper and the filter paper is transferred onto a suitable agar plate and incubate. Another technique is pour plate method where a small portion (1 mL) of the extract is mixed with molten agar medium and incubate under suitable conditions.  The choice of growth media and incubation conditions will depend on the type of microorganisms to be enumerated. For aerobic bioburden, both bacteria and fungi (yeast & molds) colonies are enumerated while for anaerobic bioburden, anaerobic bacteria colony counts are determined. The media and incubation condition and period are summarized below.

4. Enumeration

     Once the incubation period is completed, the number of colony forming unit is counted either manually or with assistance by appropriate software. Accuracy in counting the cfu is improved with the use of colony counters and microscopes.  Counting small or spreading colonies improved through experience. Using two or more personnel to do the counting improve the accuracy tremendously. 

5.  Reporting Bioburden count and average BE.

     The final bioburden counts is determine by multiplying the observed cfu with correction factor (extraction efficiency) and SIP ratio if SIP sample was done.  Bioburden may be reported as total bioburden, aerobic bioburden, fungi (yeast & molds) and anaerobic bioburden. If more than one sample per product is tested, an average bioburden estimate (Average BE) may be reported.

Bioburden Testing for Medical Devices at Sanichem Resources.

Sanichem offer a few variation of bioburden test methods to suit customers' requirement. This follow the accredited in-house method MB-BIOBURDEN-1 which is based on ISO 11737-1:2006 which will be updated to 2018 version soon. 


Bioburden and Related Tests.

1.  MB 110 - Determination of bioburden by membrane filtration (aerobic bacteria + yeast & molds) - 3 parameters

2.  MB 111 - Determination of bioburden by pour plate method (aerobic bacteria + yeast & mold) - 3 parameters

3.  MB 113 - Total aerobic and anaerobic bioburden by membrane filtration method - 5 parameters

4.  MB 114 - Total anaerobic bioburden (RCA plate)

5.  MB 115 - Total aerobic and anaerobic bioburden by pour plate method.

6.  MB 116 - Population determination of biological indicators (Etigem method)

7.  MB 117 - Population determination of biological indicators (3M method)

8.  MB 118 - Correction Factor determination for bioburden - repetitive extraction

9.  MB 119 - Correction Factor determination for bioburden - inoculation method


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