JULIUS E. OFFICER. Inhibition of the growth of agents of the psittacosis group by D-cycloserine and its specific reversal by D-alanine. J. Bacteriol. 85:707-711. 1963.-D-Cycloserine inhibited multiplication of four members of the psittacosis group in chick embryo yolk sac. D-Alanine reversed each inhibition. In infections with the agent of mouse pneumonitis, the most sensitive member of the psittacosis group tested, D-alanine competitively antagonized the growth inhibition produced bv D-cycloserine. Of a number of other potential reversing agents, only DL-alanyl-DLalanine reversed the effect of D-cycloserine on mouse pneumonitis agent. The significance of the susceptibility of the psittacosis group to D-cycloserine is discussed in light of the known mode of action of this antibiotic on bacteria. The growth-inhibiting effect of D-cycloserine (D-4-amino-3-isoxazolidone) on bacteria is competitively reversed by its structural analogue, D-alanine (Bondi, Kornblum, and Forte, 1957; Shockman, 1959; Morrison, 1962; Zygmunt, 1962). This relationship may be explained by the findings of Strominger, Ito, and Threnn (1960) that D-cycloserine inhibits both the alanine racemase and the D-alanyl-D-alanine synthetase of Staphylococcus aureus and that D-alanine competitively reverses the D-cycloserine inhibition of both reactions. Neuhaus and Lynch (1962) recently reported similar observations. Since D-1 A preliminary account of this work was presented at the Annual Meeting of the American Society for Microbiology, Kansas City, Mo.,

Evidence is presented for the presence in meningopneumonitis particles and extracts of an enzyme decarboxylating a, Ediaminopimelic acid to lysine and for the absence of a corresponding enzyme in the uninfected host. Properties of the enzyme are described and compared with those of bacterial diaminopimelic acid decarboxylases. The significance of these observations with respect to the mode of lysine biosynthesis in the psittacosis group and to its phylogenetic origin is pointed out. Bader and MIorgan (1958) observed that lysine is not required for multiplication of the 6BC strain of psittacosis agent in L cells, although this amino acid is a constituent of the agent (Ross and Gogolak, 1957) and is necessary for growth of the L cells themselves (Eagle, 1955). This suggested that members of the psittacosis group may synthesize their own lysine via a, E-diaminopimelic acid (DAP) as do bacteria (Dewey and Work, 1952; Davis, 1952). This hypothesis was tested by examining concentrated suspensions of the agent of meningopneumonitis, a typical member of the psittacosis group and also known to contain lysine (Jenkin, 1960), for diaminopimelic acid decarboxylase (Dewey, Hoare, and Work, 1954), the enzyme catalyzing the final step in the bacterial synthesis of DAP. The search was facilitated by the absence of this enzyme in the chick embryo host.

MOULDER, JAMES W. (University of Chicago, Chicago, Ill.), DOROTHY L. NovoSEL, AND ILSE I. E. TRIBBY. Changes in mouse pneumonitis agent associated with development of resistance to chlortetracycline. J. Bacteriol. 89:17-22. 1965.-A chlortetracycline-resistant mutant of mouse pneumonitis agent, a member of the psittacosis group of microorganisms, differed in several ways from the susceptible stock from which it had been derived by serial chick-embryo passage in the presence of the antibiotic. It was almost completely resistant to chlortetracycline, had a longer growth cycle, produced many more very large particles, was not neutralized by parent antiserum and vice versa, was 10 times as resistant to D-cycloserine, and was highly lethal to mice when inoculated intracerebrally. These changes probably do not occur independently of one another but are the reflection of some genetically controlled change in the surface structure of the mouse pneumonitis particle which enables the resistant mutant to multiply in the presence of chlortetracycline.