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Microbial limit testing is the quantitative and qualitative assessment of microbes or testing for microbial contamination in a sample. This test is done for:- Estimation of total viable count of fungi and bacteria, i.e. quantitative estimation. Identification of each microbe of importance by culture on selective media, i.e. qualitative estimation.
In quantitative estimation, two tests are performed, one for the total count of fungi and the other for the total count of bacteria. To determine the total population size of fungi and bacteria in a given sample. There are total four methods for microbial limit test: A) Pore plate method B) Filtration method C) Serial dilution method D) Spread plate method
Each of these methods has its own susceptibility to errors, but here we will talk about how to avoid errors in general Top 10 tips for microbial limit testing in pharmaceuticals include:
1. Media: For cultivation of test organisms, select media that support rapid growth of the organism. Recommended media are soybean casein digest broth/agar and Sabouraud’s dextrose agar/broth.
2. Media Growth Promotion Capacity: The media we are using for the growth of organisms must be chosen wisely. The media should promote inoculation of the specific organism of interest. Products should be tested for antimicrobial efficacy.
3. Time consumption: Traditional microbial limit testing methods require culture plates to be tested by a trained microbiologist at intervals of time. Hence, by using the Growth Direct system, we were able to reduce the time required for testing by about 50%. This system records the growth of culture dishes every four hours. And it can detect any pollution. This system analyzes hundreds of culture dishes at once, saving time for the microbiologist.
4. Limited accuracy: Colonies must grow to millions of cells before they can be seen with the naked eye, so counting errors can be made by a trained and experienced person. So the expert has to be very careful and try to avoid mistakes.
5. Transfer Error: Some sensitive tests require serial incubation where samples are distributed from one incubator to another at different temperatures over a period of time. Then it is better to use the Growth Direct system, which automates the process and reduces human error.
6. Data Entry: After the technician calculates, he must avoid data entry errors. While technicians can make mistakes when working with hundreds of samples, this data entry error should be avoided because it will alter the results of a well-performed test.
7. Temperature: Temperature range should be considered depending on experimental requirements. It depends on the microorganism and the culture medium.
8. Atmosphere: Appropriate atmospheric conditions must be considered aerobic, anaerobic, aerobic/facultative anaerobic, capnophilic and obligate anaerobic.
9. pH: Any microorganism needs a suitable range of pH for growth. Any deviation from pH will inhibit microbial growth even if other conditions are favorable. An appropriate pH is required for enzyme function and metabolic activity of microbes.
10. Sterile conditions: While performing MLT, it is essential to maintain sterile/aseptic conditions. Any contamination must not invade the test, otherwise it will affect the results.
