Biological properties of Rickettsia prowazekii strains isolated from flying squirrels

Four strains of Rickettsia prowazekii, isolated from flying squirrels (Glaucomys volans volans) from Florida and Virginia, were compared with other strains of the typhus biotype, two previously established strains each of R. prowazekii and R. typhi and one strain of R. canada, for similarities in a number of unrelated phenotypic characteristics. R. akari served as a spotted fever biotype control. All strains produced small plaques on chicken embryo cell monolayers that were clearly recognized only after 10 days of incubation at 32 degrees C. All strains were highly susceptible to erythromycin. The Renografin density gradient centrifugation procedure of separating rickettsiae from the infected yolk sacs of surviving chicken embryos was equally satisfactory in all cases and resulted in moderate to large yields of purified rickettsiae. There was relatively small variation in specific hemolytic activity or specific CO(2) formation from glutamate. None of the strains catabolized glucose. There was some strain variation in virulence for the chicken embryo, but none of the above tests separated the three species of the typhus biotype. On the other hand, R. akari was clearly distinguished by its more rapid plaque formation and by higher resistance to erythromycin. It is concluded that by the tests conducted thus far, the biological properties of the flying squirrel strains do not differ substantially from those of other strains of the typhus biotype.