Effects of “K” Medium on the Filterability of Bacteria

Abstract

Kendall employed a culture medium 1 consisting presumably of whole undenatured protein, devoid of all products of digestion which he referred to as peptones. He reported the transformation of ordinary bacteria into primitive forms capable of passing filters presumably impervious to the passage of normal bacteria. 2 Kendall concluded that he was dealing with unusual forms of bacteria, not only on the basis of their filterability, their appearance under the dark-field microscope, and their irregular staining, but also because of his inability to obtain sub-cultures by transplantation of the “filterable” forms to ordinary media, whereas sub-cultures were obtained by similar transplantation to his own, so-called K medium.

We here summarize some of our experiments to acquaint ourselves with this apparently new and important phenomenon.

The appearance of viable and cultivable bacteria in the filtrates of bacterial cultures has been repeatedly recorded. It is generally understood, that the mere passage of cultivable bacteria through filters does not predicate any radical change in their original size. It has been repeatedly shown that under a variety of conditions, normally effective filters may become permeable to bacteria of ordinary and even large size.

Even the first few experiments convinced us that in the case of cultures grown on K medium, the frequency of passage and the numbers of viable units of bacterial protoplasm appearing in the filtrates at each filtration were considerably greater than in the case of cultures grown on ordinary media. Furthermore, the filterability of cultures grown in K medium was the greater the more profuse was the growth attained at the time of nitration. Increased growth could be secured by the addition of carbohydrates or peptone to the K medium and in either case the filterability was increased, thus it is evident that the exclusion of peptones from the medium is certainly not responsible for the increased filterability of Kendall's cultures.