Microbiology: Sterility Tests
The sterility test is a technique that microbiologists use to determine whether or not an object, such as medical equipment or food packaging, has been contaminated by any microorganisms. It can be used on the surface of the item or to take samples from inside it.
A sterility test produce two types of results: negative and positive. A negative result means that there are no harmful bacteria present, while a positive result indicates the presence of one or more species that could cause harm if left untreated.
Methods of Sterility Testing
Sterilization is a process that eliminates or kills all forms of life, including harmful microorganisms. Methods of sterilization are classified into two categories: physical and chemical.
Physical methods do not use any chemicals or heat, while chemical sterilization involves applying gas to kill all forms of life on an object. Sterility testing is often performed after the completion of either type of method for two reasons:
- To ensure that there are no remaining microorganisms present after the sterilization process
- To determine whether or not microorganisms were able to enter into an object that was previously sterilized after its initial creation
Sterility Test
There are several types of sterility test. These are:
1. The filter paper method
A sterilized metal wire acts as a support for the sterile filter paper. The object that has been prepared is placed on top of this. Any microorganisms present will be drawn up by capillarity into the filter paper. Any harmful bacteria within it can then grow in an incubator or culture medium.
2. The swab method
A sterile cotton swab is rubbed over the surface of an object to collect any microorganisms present. It is incubated in a culture medium for up to two weeks so that bacteria within it can grow and multiply. The culture will allow microbiologists to identify how much contamination there was and which species of bacteria were present.
3. The aerobic plate count (APC) method
This sterility test determines any harmful microorganisms on an object, but it does not identify what type they are. A culture medium with agar and nutrients is prepared for this purpose. The object in question will be placed into the medium. The bacterium will then be allowed to grow and multiply in an incubator for up to 48 hours, at which point it can be examined under a microscope.