Which rickettesiae are able to grow in cell free media?
Ans. is 'a' i.e., R. Quintana . Rickettisiae are obligate intracelluar organisms. So they cannot grow in cell free medium. But, there is one exception to this rule, R. Quintana which is not an intracellular parasite, so can grow in cell free media.
R. Quintana
R. Rickettsii
R. Typhi
R. Tsutsugamushi