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Units Used in Microbiology Results Interpretation

Microbiology is a branch of science dealing with the study of microorganisms in the matter. In the food industry, there are various tests conducted to establish the quality and safety of food products. The results use various units. As such, it is important for industry participants, especially producers and marketers to have an understanding of different measurement units to be used in microbiology results interpretation.

Below we have put together a simple guide on commonly used measurement units when it comes to microbiology results interpretation.

Meaning of CFU in Microbiology
Some of the most significant tests when it comes to food safety and quality entail measuring the bacteria load in various samples under given incubation conditions. Different types of bacteria developing in a sample are identified and measured in Colony Forming Units. This simply means the different groups of bacteria identified as developing in the sample. To make more sense of the tests, the CFU microbiology result is expressed per unit of the measure concerning the sample. The common expressions used here include CFU/g or CFU/ml. Grams (g), or millilitre (ml) is used depending on whether the sample is a solid or liquid respectively.

Parts per Million (PPM)
Another common unit of measurement used in microbiology results interpretation is PPM (Parts per Million). The unit is derived from the metric system, in which units are measured in 10s, 100s, and 1000s. When dealing with solids, we know that 1 kg= 1,000g. Therefore a gram is 1/1000 of a kilogram. Since 1g = 1,000mg; a milligram is 1/1,000 of a gram. We can, therefore, derive that a milligram is 1/1,000,000 of a kilogram. This shows that a milligram is a part per million (PPM) of a kilogram, giving us the unit mg/kg.

It is worth noting that at one standard atmosphere and 4 degrees centigrade, a liter of pure water weighs 1kg. As such, 1 ppm, mg/kg = mg/L in these conditions.

Parts per Billion (PPB)
This unit is used to express an even smaller concentration than PPM. Parts per Billion (PPB), are used to mean one part in a billion when it comes to microbiology results interpretation. If 1mg = 1,000 µg; ppb is 1/1000, 000,000 µg/L. It is important to ensure that you do not confuse ppm in terms of mg/L and ppb expressed as µg/L (microgram per Litre). 

The above units are usually used in microbiology results interpretation on food quality and safety tests. In most cases, the test is used to establish contamination levels in food products including water. The right units must be used every time to ensure that the correct interpretation is made as simple mistakes could be costly and even fatal. 
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Author avatar obgtmljsno 1 month ago

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