Experiments on the Use of the K Medium

Abstract

One of the most striking of recent contributions on bacterial variability has been that of Kendall, 1 who reported the preparation of a special medium in which ordinary bacteria developed a filterable or “virus-like” stage. A number of the commoner bacteria, when inoculated into this medium, were converted within a short time to a form which passed Berkefeld filters and which could not be cultivated on ordinary media. Not only was the “K” medium effective in promoting such a change, but it was claimed to be effective also in bringing about the opposite process, namely reversion from the filterable form to the usual visible organism.

Since such a method, if effective, would place in our hands a valuable tool for the study of many debated problems on bacterial variability, an investigation of the K medium was undertaken in this laboratory.

Several different lots of this medium were employed. One was prepared from hog intestine according to Kendall's directions. After the alcohol and benzene extractions, the preparation was dried, ground and kept in a stoppered container. At the time of use, the proper quantity of the powder was placed in test tubes or flasks and Tyrode solution added to give a 2% suspension. The pH of the medium was adjusted to 7.4. After autoclave sterilization the medium was somewhat turbid with considerable sediment. In addition to our own preparation, 2 experimental lots prepared by the Difco laboratories were used. The first of these, also prepared strictly according to Kendall's directions, produced a medium quite similar in appearance to our own. The second had been subjected to a more thorough extraction and washing and resulted in a much clearer medium.