This document or any portion there~of may not be reproduced without specific authorization from the Commanding Officer, Biological Laboratories, Fort Detrick, Frederick, Maryland; however, ASTIA is authorized to reproduce the document fot U1.S. Government purposes. The information in this report has not been cleared for release to the general public ASTIA AVAILABILITY NOTICE Quý.alified requestors may obtain copies of : this document from ASTIA. Foreign announcement and dissemination of this document by ASTIA is limited.

Loss of the genetic determinant for pesticin I in Pasteurella pestis results in concomitant loss of the plague coagulase and fibrinolytic factor. The median lethal dose for mice of an isolate lacking only these activities is increased by factors of about 10 1 , 10 4 , and 10 7 cells when administered by the intravenous, intraperitoneal, and subcutaneous routes, respectively. Virulence of the aforesaid strain can be enhanced in mice treated with 40 μg of ferrous iron. This response resembles that of Pasteurella pseudotuberculosis , a closely related species that normally lacks pesticin I.

No abstract

Pasteurella pestis within neutrophiles and macrophages removed from the peritoneal cavity of guinea pigs during experimental plague were shown to be viable by direct microscopic observation of the infected phagocytes incubating in suitable bacteriologic media. The time-honored hypothesis that the major determinant of the virulence of the plague bacillus is its ability to resist ingestion by phagocytes must be reevaluated.

No abstract

Mutational loss of pesticin I, a bacteriocin-like substance produced by Pasteurella pestis, is known to result in concomitant loss of a coagulase and fibrinolytic factor. No relationship was detected between pesticinogeny and other tested properties either associated with virulence or peculiar to P. pestis. Pesticin I was distinguished from the coagulase and fibrinolytic activities on the basis of anatomical distribution, behavior during gel filtration, and sensitivity to heat. Coagulase and the fibrinolytic factor were not differentiated by these criteria. Spontaneous suppressor mutations causing reversion to pesticinogeny were not detected, nor were such mutants obtained by treatment with ultraviolet light or 2-aminopurine. Attempts to demonstrate a common activator of pesticin I, coagulase, or the fibrinolytic factor in extracts of pesticinogenic cells were not successful. These results are in accord with the hypothesis that at least two structural genes for the three activities reside on a replicon distinct from the chromosome proper. Fibrinolytic activity was significantly reduced in the presence of 0.003 M e-aminocaproic acid and was nonexistent on fibrin films freed from endogenous plasminogen by treatment with heat. Fibrinolytic activity on heated films could be restored by addition of plasma or serum from six mammalian species. Accordingly, the plague fibrinolytic factor, like staphylokinase or urokinase, promotes the conversion of plasminogen to plasmin.

The Pasteurella species implicated as the etiologic agent of a massive white perch mortality in the Chesapeake Bay and first described by S. F. Snieszko et al. has been characterized further in our laboratory. The general morphology and physiology of this organism is similar to that of the pasteurellae and several known fish pathogens. There are enough dissimilarities, however, to rule out its identification with any established species. The organism is obligately halophilic and grows in a temperature range between 17 and 31 C on ordinary media containing 1% NaCl. It has a relatively narrow range of pH, temperature, and salinity tolerance, and a very short survival time in spent media or brackish water, in contrast to Pasteurella pestis and P. pseudotuberculosis. Serological tests also indicate that this organism is distinct from other species which it resembles. On the basis of classic morphological and physiological criteria, this organism fits best in the genus Pasteurella; the species name piscicida (L. noun piscis, a fish; L.v.L.adj. suffix-cidus, to kill; M.L. noun piscicida, fish killer) is proposed.

No abstract