In: Biology
Which test of the Multiple Tube fermentation Technique determines the MPN of a sample?
1. Confirmed
2. Plate count method
3. Completed
4. Presumptive
Most Probable Number (MPN) could also be a way used to estimate
the concentration of viable microorganisms during a sample by means
of replicate liquid broth growth in ten-fold dilutions. It is
commonly utilized in estimating microbial populations in soils,
waters, agricultural products and is particularly useful with
samples that contain particulate material that interferes with
plate count enumeration methods. MPN is most ordinarily applied for
quality testing of water i.e) to make sure whether the water is
safe or not in terms of bacteria present in it. A group of bacteria
commonly referred as feacal coliforms act as an indicator for
faecal contamination of water.
PRINCIPLE
Water to be tested is diluted serially and inoculated in lactose
broth, coliforms if present in water utilize the lactose present
within the medium to provide acid and gas. The presence of acid is
indicated by color change of the medium and therefore the presence
of gas is detected as gas bubbles collected within the inverted
durham tube present in the medium. The number of total coliforms is
set by counting the quantity of tubes giving positive reaction (i.e
both color change and gas production) and comparing the pattern of
positive results Most Probable Number Method (MPN).
MPN test is performed in 3 steps
• Presumptive test • Confirmatory test • Completed test