[Methylotrophic bacteria in the sphere of drinking water. 1. Communication: comparison of the bacterial count of the water derived from different treatment plants].

Raw water, biological filters as well as supply water of 11 different treatment plants were examined with respect to the occurrence of methylotrophic bacteria. Although these organisms could be found in all samples, there were considerable differences in relation to the countable numbers. Methane containing raw waters showed only very low numbers of methylotrophic bacteria, whereas after aeration and passing the biological filters the effluent contained high numbers of these organisms. No correlation could be observed between colony count of the heterotrophic bacteria and the number of methylotrophic bacteria. A rapid method for determination of the methylotrophic bacteria on solid media, using the different colony size depending on incubation with and without a C1-compound, is quite inaccurate and uncertain.