Regarding the MF technique, the coliform group is defined as facultative anaerobic, gram-negative, non-spore-forming, rod-shaped bacteria that develop colonies with distinctive characteristics on specific media. Rarely, on m-Endo medium, typical bright colonies may be produced by non-coliform organisms, and atypical colonies (colonies with pink, crimson, or non-luminous nuclei) may be coliform bacteria; therefore, confirmation of all typical and atypical colonies is recommended.
The MF technique can be used to test drinking, surface, ground, swimming pool and sea waters. Only unless the sample is diluted, as a high turbidity level can quickly clog the membrane filter before sufficient sample is collected.
The MF technique is not used to test wastewater treated with primary treatment.
The SM 9222H test apparatus is tested with each lot of positive and negative culture controls prior to use. 20 to 30 mL of dilution or rinse water is filtered through the filter to check for coliform contamination at the beginning and end of each filtration series. If controls show contamination, all data on affected samples
rejected and new samples are requested.
To count colonies on membrane filters, a low-power (10 to 15 ) binocular wide-field dissecting microscope or other optical device with a oriented cool white fluorescent light source is used to provide optimum imaging. Under normal ambient light, all red and blue to purple colonies are counted and recorded as the total coliform result. Only blue to purple colonies are counted and recorded as an E. coli result. Clear or white colonies are acceptable.
Coliform verification: Total coliform and colony verification is not required for drinking water. For waters other than drinking water, verification should be done at the frequency determined by the laboratory. Depending on the need and sample type, laboratories may adopt more stringent QC measures (for example, 10% of positive samples should be confirmed if at least one colony of each typical or atypical colony type is confirmed from a particular membrane filter culture). Their number should be adjusted according to the validation results.
Our organization, among numerous test, measurement, analysis and evaluation studies, with its trained and expert staff and advanced technological equipment, within the framework of national and international standards, offers total coliform and E. coli simultaneous respiti testing services.
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