Decomposition of Urea by Proteus

Abstract

At the Third International Congress for Microbiology St. John-Brooks and Rhodes 1 suggested a simplification of the taxonomy of the Proteus genus. On the basis of maltose fermentation and indol production 3 species were set up in the genus, indologenes (vulgaris), morganii, and anindologenes (mirabilis). Proteus americanus and Proteus ammoniœ were considered variants of anindologenes. Proteus hydrophilus, Proteus pseudovaleriei, and Proteus icthyosmius were excluded from the genus on the basis of their ability to ferment mannitol.

The decomposition of urea with formation of ammonia is one of the major criteria for the determination of the Proteus group (Bergey). 2 This phenomenon, however has received relatively little attention, particularly when recent additions have been made to this genus. From a review of the literature it appears that the action on urea of Proteus morganii, Proteus hydrophilus, Proteus icthyosmius, and Proteus bombycis is unknown.

Investigators, with few exceptions, have used sterile urine as a culture medium to test urea decomposition by Proteus. Complications arising from the use of such a variable medium are obvious. Moltke 3 and Yacob 4 employed a medium consisting of 2% urea in 0.85% saline. These investigators point out that substances in the inoculum initiate growth and we have found that serial transplants in their medium fail to grow. After several attempts a medium of known composition has been devised, in which small inocula grow and in which serial transplants can be made.

Materials and Methods. The medium finally employed contained 2% urea (Merck), 0.01% yeast extract (Difco), and M/15 primary and secondary phosphate buffers (Sorensen) in distilled water to give a final pH of 6.8. Sterilization was accomplished by filtration through Berkefeld filters (Type N). The test medium was inoculated from 24-hour agar cultures and incubated at 37° C. Nessler's reagent was employed to determine the presence of ammonia by adding a loopful of the culture to a drop of the reagent on porcelain plates.