Quantitative study on the reproduction of virulent and vaccine Rickettsia prow azeki strains in cells of different origin.

Vaccine and virulent strains of Rickettsia prowazeki differ by the degree of reproduction in McCoy, B, and chick embryo cells but replicate to similar levels in FL cells. As distinct from the virulent Breinl strain, the vaccine E strain rickettsiae permanently lost their capacity for long-term reproduction in McCoy cell cultures but retained their capacity to adsorb on to and penetrate into these cells. Consequently, the reproduction of rickettsiae is limited at later stages of intracellular infection. The E strain of R. prowazeki has been defined as a conditional lethal, host-dependent (hr) mutant.