Difference Between MPN and CFU

Is there a difference? CFU refers to “colony forming units”, whereas MPN refers to “most probable number”. The difference is that CFU/100ml is the actual count from the surface of a plate, and MPN/100ml is a statistical probability of the number of organisms (American Public Health 2012).

1. How is MPN calculated?
2. How many CFU are considered countable?
3. What is the difference between a colony a CFU and a bacterial cell?
4. What is MPN Coliform bacteria?
5. What are the test used for MPN?
6. What does MPN 100 mL stand for?
7. What is considered the most accurate countable range for colonies on a plate?
8. What is the most widely used method of counting bacteria?
9. What is an acceptable aerobic plate count?
10. Why do we use CFU?
11. How many bacterial cells does it take to make a colony?
12. What does CFU stand for?

How is MPN calculated?

The MPN Table (Table 4) is based on 3 dilutions of decreasing decimal increments. Example: Five tubes of undiluted sample, 5 tubes of 10X dilution, and 5 tubes of 100X dilution are inoculated initially. Positive results are obtained from 5 of the undiluted samples, 5 of the 10X dilutions, and 3 of the 100X dilutions.

How many CFU are considered countable?

ASTM provides countable ranges of 20-80 CFU/membrane, 20-200 for spread plates and 30-300 for pour plates (7). The FDA Bacterial Analytical Manual (BAM) recommends 25-250 CFU/plate as a countable range (8).

What is the difference between a colony a CFU and a bacterial cell?

In microbiology, colony-forming unit (CFU) is a measure of viable bacterial or fungal numbers. Unlike in direct microscopic counts where all cells, dead and living, are counted, CFU measures viable cells. ... These colonies are clearly different between each other, both microscopical and macroscopical.

What is MPN Coliform bacteria?

MPN is most commonly applied for quality testing of water i.e to ensure whether the water is safe or not in terms of bacteria present in it. A group of bacteria commonly referred to as fecal coliforms act as an indicator of fecal contamination of water.

What are the test used for MPN?

The most probable number (MPN) is a statistical method used to estimate the viable numbers of bacteria in a sample by inoculating broth in 10-fold dilutions and is based on the principle of extinction dilution. It is often used in estimating bacterial cells in water and food.

What does MPN 100 mL stand for?

CFU refers to “colony forming units”, whereas MPN refers to “most probable number”. The difference is that CFU/100ml is the actual count from the surface of a plate, and MPN/100ml is a statistical probability of the number of organisms (American Public Health 2012).

What is considered the most accurate countable range for colonies on a plate?

Most textbooks and lab manuals typically recommend using plates that yield somewhere between 30 and 300 colonies (or some similar range). Too few colonies, and the count may not be accurate; too many colonies, and it is difficult as well as time-consuming to distinguish the individual colonies on a plate.

What is the most widely used method of counting bacteria?

The two most widely used methods for determining bacterial numbers are the standard, or viable, plate count method and spectrophotometric (turbidimetric) analysis. Although the two methods are somewhat similar in the results they yield, there are distinct differences.

What is an acceptable aerobic plate count?

Dilution factors may exaggerate low counts (less than 25), and crowded plates (greater than 250) may be difficult to count or may inhibit the growth of some bacteria, resulting in a low count. Report counts less than 25 or more than 250 colonies as estimated aerobic plate counts (EAPC).

Why do we use CFU?

A colony-forming unit (CFU, cfu, Cfu) is a unit used in microbiology to estimate the number of viable bacteria or fungal cells in a sample. ... Counting with colony-forming units requires culturing the microbes and counts only viable cells, in contrast with microscopic examination which counts all cells, living or dead.

How many bacterial cells does it take to make a colony?

The division time for E. coli and similar microorganisms ranges from 20 minutes to 1 hour. Thus a single E. coli cell, which divides approximately every 30 minutes, can grow into a colony containing 10⁷ – 10⁸ cells in 12 hours (2²⁴ = 1.7 × 10⁷).

What does CFU stand for?

A colony forming unit, or CFU, is a unit commonly used to estimate the concentration of microorganisms in a test sample. The number of visible colonies (CFU) present on an agar plate can be multiplied by the dilution factor to provide a CFU/ml result.