The Most Probable Number (MPN) test is a statistical estimation technique used in microbiology. It's primarily employed to determine the concentration of viable microorganisms in a sample.
The MPN method is especially useful for analyzing samples that are turbid or contain particulate matter. It provides an estimate of the number of bacteria based on the probability theory.
The test involves multiple tubes being inoculated at different dilutions to estimate bacterial concentration. Positive results are typically indicated by gas production in lactose broths
The MPN test is commonly used for detecting coliform bacteria in water samples. It serves as an indicator of the sanitary quality of foods and water.
The presence of coliforms suggests possible contamination with fecal matter. The MPN test involves three sequential tests: presumptive, confirmed, and completed tests.
Eosin Methylene Blue (EMB) agar is often used, where coliforms produce colonies with a metallic sheen. The MPN method is an alternative to the membrane filtration method for water testing.
It's particularly beneficial for samples that cannot be filtered easily, like those containing mud or sludge. The test is labor-intensive and requires multiple test tubes and incubation steps.
Results from the MPN test are expressed as a range, indicating the statistical nature of the method. While it's a valuable tool, the MPN test has a relatively large margin of error compared to direct counting methods.
The MPN method is not suitable for all types of microbial analyses due to its inherent variability. Despite its limitations, the MPN remains a standard method in many water quality laboratories worldwide.
Regular monitoring using the MPN test helps ensure the safety of drinking water and reduces the risk of waterborne diseases. In summary, the MPN test is a crucial tool in environmental microbiology, ensuring the microbial safety of water and food products.