Microbial Load Tests

Microbial Load Tests

The microbial count test, also called the biological load test or microbial load test, is performed to monitor the raw material, process samples, and microbiological content in the pharmaceutical, biological, cosmetic, nutritional products and medical device industries. . The FDA expects companies to monitor the burden of biological load on products used for humans and animals. The biological load test can be carried out in several ways, depending on the nature of the material being tested.

 A list of extraction methods presented below. The extraction method is the procedure for removing microorganisms from the product being tested.

 ⦁ Immersion

 ⦁ Washing / Rinsing

 ⦁ Surface Sampling

 ⦁ dilution

 A list of the numbering methods presented below. The numbering method is the procedure used to determine the number of viable microorganisms extracted from the product being tested.

 ⦁ Membrane Filtration

 ⦁ Direct coating

 ⦁ Most Likely Number (MPN)

 The microbial load test should be verified to ensure that the method is effective, accurate and reproducible in determining the microbial load of material in a test product. The most appropriate methodology should be identified as part of method development. Verification will be performed by the method showing the best recovery of the organisms without any inhibition. Validation is performed per USP / EP for Pharmaceutical or Biotechnology products and AAMI for medical devices. Cosmetics are tested per FDA BAM guide.

 MQA may also develop specific bio-incineration procedures for samples that are difficult to test.


 Once the sample has been prepared, several methods are available to determine the total number of cells in the food. Many of these methods also allow counting of important bacterial groups such as coliforms. A few people may allow you to count the number of germs of a particular genus, such as Salmonella. 1. Standard Plate Count (SPC) The most commonly used method for determining the number of colony forming units (CFUs) in a food. Use a smear or spill plate containing a homogenized food sample (psychrotrophs may not survive on spill plates). Incubation is 35 ± 48 hour aerobics at 2 o C. Number of APC-aerobic plates - cells aerated on the agar surface and incubated aerobically.


  1. Easy to perform
  2. AOAC (Official Association of Analytical Chemists) approved for many foods


  1. Results are not available for at least 16-18 hours (usually longer).
  2. Counts in a food are affected by several factors, including:
  3. Sampling method and MO distribution in foodstuff
  4. The nature of food flora (mostly takes mesophilic aerobes and aerobes)
  5. Nature of food
  6. The internal parameters of the growth medium reflect the perceived MO.
  7. Incubation time and temperature (external parameters)
  8. Microbial antagonism among food species
  9. Spiral Plate Counter - An automatic version of the SPC is a spiral plate (a dispensing arm that acts only as a needle on a recoil), a device that distributes a continuously decreasing volume of liquid on a single rotary agar plate. The agar is then incubated and counted. 10 on a single plate can deliver effectively up to the 5 concentration range, but the numbering requires a special counting grid.

 Advantages over SPC:

  1. Easy to perform (little training required)
  2. Less material used (agar plates, dilution cavities, pipettes)
  3. 3-4 X can run more samples per hour
  4. Spiral coating is an AOAC method which is well understood with SPC values.


  1. Food particles can clog the dispensing arm - more suitable for liquids such as milk
  2. Dry Petrifilm

 Iki Two plastic films held together on one side and covered with a sandwich

 ⦁ components of culture media, tetrazolium dye (decreasing dye) and water