CHANGES IN MOUSE PNEUMONITIS AGENT ASSOCIATED WITH DEVELOPMENT OF RESISTANCE TO CHLORTETRACYCLINE.

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.