No abstract

Glutamate catabolism and the factors contributing to metabolic stability of purified suspensions of Rickettsia rickettsi were investigated. By use of 14 C-glutamate, it was shown that CO 2 was produced from all carbons of glutamate and that 14 CO 2 production was reduced by the addition of most of the unlabeled intermediates of the citric acid cycle and pyruvate. Oxalacetate, added in various concentrations, did not stimulate glutamate utilization. When the cells were suspended in bovine plasma albumin (BPA), CO 2 production from glutamate proceeded at a nearly uniform rate for 8 hr at 32 C and for 24 hr at 15 C. When BPA was used, the cells retained their metabolic activity at 0 or 30 C regardless of cell concentration, and were not influenced by the addition of varoius metabolites. Without BPA, metabolic stability was directly related to concentration. Of the stabilizers tested on low concentrations of rickettsiae, reduced glutathione was the most effective, provided that the gas phase contained predominantly N 2 . Under these conditions of low partial pressure of O 2 , glutamate further stabilized metabolic activity and was actively metabolized. The cells were also stabilized by oxidized glutathione in a gas phase of air, but under these conditions glutamate was utilized at a more moderate rate and it impaired metabolic stability.

described a medium on which, with few exceptions, only Staphylococcus aureus strains that clot blood are able to grow, producing large black colonies. The following modification of that medium was used to compare the number of organims grown on it with the number of similar organisms grown on staphylococcus medium number 110 (Chapman: Trans. N. Y. Acad. Sci., 9, 52, 1946). Medium consisting of agar, 25 g; mannitol, 10 g; K2HPO4, 5 g; LiCl, 5 g; yeast extract, 3 g; tryptone, 10 g; and water, 1,000 ml was adjusted to pH 9.2, sterilized by boiling, and cooled to 55 C. One ml of 5 per cent potassium tellurite was then added, and the cultures were incubated for 48 hours at 37 C.Of 232 cultures plated on both media, there was complete agreement in 83 per cent; 5 per cent showed from 1 to 10 colonies on Ludlam's medium but none on no. 110; 6 per cent that did not clot blood showed growths on Ludlam's medium; and one colony on no. 110 belonged to the genus Flavobacterium.Therefore, for the highest recovery of blood-coagulating staphylococci, cultures should be plated on both media. But if only one is to be used, staphylococcus medium no. 110 is preferable because of the several cultures containing a large number of organisms that failed to grow on Ludlam's medium. Also this medium, unlike no. 110, cannot be used for the direct application of confirmatory tests. Most of the instances in which Ludlam's medium alone showed from 1 to 10 colonies are of questionable, significance.