Properties in culture and persistence in cotton rats of the Rickettsia prowazekii vaccine strain E and its mutants.

Cultural properties and the capacity for persistence were studied in spontaneous erythromycin-resistant (E errSM), in induced erythromycin-resistant (E errI) mutants and in a virulent revertant (E Vir) of the vaccine strain E, as compared with parent vaccine strain E and standard virulent strain Breinl of Rickettsia prowazekii. Cultural properties of the strains were found to differ in passages in chick embryos (CE) and cultures of FL cells. Multiplication indices in CE of mutant E errI were significantly lower than those of other strains (E, E errSM, E Vir, Breinl). The multiplication rate in FL cells was found to be high in strains E errSM, Breinl, E Vir, being much lower in strains E errI and E. The capacity of the virulent revertant E Vir to persist in cotton rat (CR) was higher as compared with that of standard strain Breinl and significantly higher than that of the parent strain E. Low level carrier state of rickettsia was registered in CR infected with the mutant E errI.