membranfiltrationsprov

Membrane filtration test, or membranfiltrationsprov, is a microbiological technique used to detect and quantify microorganisms in liquid samples by filtering a known volume through a sterile membrane that traps cells. The membrane is then placed on an appropriate culture medium and incubated under conditions selective for the target organisms. After incubation, colonies on the membrane are counted and expressed as colony-forming units per unit volume (CFU/mL or CFU/100 mL).

Procedure and principles

A sample is passed through a membrane with a pore size typically around 0.45 micrometers under sterile conditions. The membrane is then transferred to a selective or differential agar plate or into a suitable broth for growth. Following incubation, visible colonies indicate viable organisms present in the original sample. This method enables enumeration of low concentrations by allowing filtration of larger volumes than some plate methods.

Applications

Membrane filtration is widely used in water quality testing (drinking water, treated wastewater, and recreational waters) to enumerate total coliforms and Escherichia coli, among other target microbes. It is also employed in food and beverage safety, and in pharmaceutical or environmental monitoring where rapid, quantitative microbial assessments are needed.

Advantages and limitations

Advantages include high sensitivity, the ability to process relatively large sample volumes, and direct enumeration of viable cells. Limitations involve potential filter clogging by particulates, the need for sterile technique, and the requirement that organisms grow on the chosen media. Some organisms may be stressed by filtration or may not form colonies on the selected medium, affecting results.

Standardization

Membrane filtration methods are described in national and international standards and guidelines, including ISO and national environmental agencies, with specific media and incubation conditions tailored to the target organisms.