During recent sampling for E. coli, most of the sample results were significantly larger then the Fecal numbers. What could possible cause this? Method was membrane filtration reporting in CFU.
There can be few factors.
What incubation temperatures were used for each bacteria type (E. coli vs. fecal coliforms)? Ideally 35-37C would be optimal for the E. coli, but 44C for fecal coliforms. If you're incubating fecal coliforms at 35-37C, the growth may not be an accurate indicator and the E. coli counts would be higher.
What kind of water matrix were you testing? Was it an extraction from soil? You can end up having high turbidity or unclean water samples that have heterotrophic counts that inflate E. coli counts or hamper your ability to get an accurate count.
Thank you for this, medium is water and I have to verify via the lab we contract the incubation temperatures, which may end up explaining a lot.
However, fecal coliforms would encompass the entire population of E. coli in addition to other coliforms of fecal origin, so that may not support my idea about temperatures (although the temps mentioned are standard procedure).
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