By April Wanstrom, IDs Department Scientist, BS, RM/SM (NRCM) CQA (ASQ)
Medical device manufacturers generally perform bioburden testing on samples and environmental monitoring on manufacturing facilities. The result of both tests is a count of the number of microorganisms present. It is important to identify the microorganisms represented by the count. Microbial identification testing tells you what types of microorganisms are present.
Genetic and Vitek are two different test methods used to identify microorganisms. Microbial identification allows manufacturers to know what types of microorganisms are present and investigate sources for the microorganisms and resistance to sterilization methods.
The genetic test uses a portion of the DNA that codes for the 16S ribosome to identify bacteria. A different segment of the ribosomal DNA is used to identify yeast and filamentous fungi. This DNA changes little because ribosomes build proteins within the cell and changes can be deadly to the microorganism. Once DNA sequencing is complete library resources can be searched to identify the unknown microorganism.
The cost of materials used in genetic testing is typically three times higher than materials for Vitek testing. This results in a higher charge for a genetic test to the manufacturer.
Vitek is an identification system that can identify bacteria and yeast. This test uses biochemical reactions and nutrient usage of the microorganism to make the identification. The test requires that a sufficient amount of growth be obtained during a set growth period of 18 – 70 hours. Depending on culture conditions the reactions of the microorganism may change.
Vitek cards containing 64 wells with nutrients and biochemical test are used for testing. A solution of the microorganism is made to inoculate the card. As the microorganism reacts within the card a pattern of positive and negative reactions develop. This pattern is compared to a library providing a name for the bacteria or yeast.
If an unknown microorganism doesn’t match any of the library entries by at least 85 percent, the Vitek software determines it to be a no match to the library microorganisms. When this occurs, additional testing should be considered.
Choosing a test method
When deciding on an appropriate method for identification consider: what types of microorganisms need to be identified, the microorganisms in the library of the test system, the cost, and in which direction regulatory bodies or the industry are leaning. The FDA has shown interest in genetic testing for positive sterility tests. The FDA has also shown preference for a polyphasic approach to microbial identification. A polyphasic approach involves considering multiple characteristics of the microorganism (colony morphology, Gram stain, growth temperature, etc.) and an identification method to obtain a name.
For medical device manufacturers who need to identify microorganisms, Vitek is a cost effective solution. Most pharmaceutical manufacturers face more regulation, so it is generally best to choose genetic testing. When a test of sterility shows growth, it is best to choose genetic testing as the identification method.
For more information on which test would be best for you, contact Nelson Labs.