ISO 8199:2018 pdf free

ISO 8199:2018 pdf free.Water quality – General requirements and guidance for microbiological examinations by culture
Clean and dirty water should be separated and processed using separate equipment in separate areas to reduce cross-contamination risk where possible. Alternatively, process batches of clean waters before dirty water.
Before examination, mix the sample thoroughly by agitation to achieve uniform distribution of microorganisms and other particles. This can be achieved by inversion of the sample or by a to-and-fro motion. Depending on the nature of the water and the microbial content anticipated, make any necessary dilutions at this stage.
For plate counts, ten-fold dilutions are usually used. For membrane filtration (with a smaller surface area), smaller dilution steps are recommended. For many most probable number ( MPN) techniques,dilutions are an inherent part of the procedure. Refer to 9.2.3 for guidance on dilutions in MPN techniques. See ISO 6887-1[2] for general guidance on the preparation of serial dilutions.
For ten-fold dilutions, aseptically measure nine volumes of the diluent and one volume of the water sample into sterile dilution bottles or tubes. Alternatively, volumes of diluent pre-sterilized in screw-capped bottles are used and volumes verified after autoclaving. One or more ten-fold dilutions are made by transferring one volume of water sample to nine volumes of diluent. Mix the solution thoroughly with a fresh pipette or by mechanical means and transfer one volume of this dilution to another nine volumes of diluent. Repeat these steps as many times as required. Prepare sufficient volumes of each dilution for all the tests to be carried out on each water sample.
For dilutions of other magnitudes, the volume of diluent to volume of sample is adjusted accordingly.For example, four-fold dilutions can be made as described above for ten-fold dilutions, only in this case one volume of water sample is mixed with three volumes of diluent. Another approach is to use a ten-fold dilution series, but filter both 10 ml and 30 ml volumes.
If the concentration of the target organism is expected to be high, hundred-fold dilution steps may be used by mixing one volume of water sample with 99 volumes of diluent, but such large intervals between measurements can adversely affect the reliability of the test results.ISO 8199 pdf download.