Rickettsia mooseri / Rickettsia typhi - Morphology, Culture, Neill-Mooser/Tunica reaction
Introduction to Rickettsia mooseri / Rickettsia typhi
It is the causative agent of endemic or murine typhus. It is transmitted via rat flea bite, infected saliva or feces aerosolized and inhaled, or ingestion of food contaminated with rat urine or flea feces.
There has been no evidence of no man-to-man transmission.
Morphology of Rickettsia mooseri / Rickettsia typhi
Morphologically, Rickettsia mooseri / Rickettsia typhi is a gram-negative bacillus. They are obligate, intracellular, fastidious micro-organisms with a size of 0.3 x 1-2 μm and are pleomorphic.
They multiply by binary fission within the cytoplasm of eukaryotic cells. The target cell is the Reticuloendothelial system and the release of mature rickettsiae results in the lysis of host cells. The bacterium has a very small genome composed of 1-1.5 million bp.
Rickettsiae are primary pathogens of arthropods (lice, fleas, ticks, mites) and are present in the intestinal tract- transmitted by arthropod vectors. They are non-capsulated and non-motile; a loose slime layer is present. It has LPS and peptidoglycan layer and LPS shows weak endotoxic activity.
They are poorly Gram-stained but stained well with Giemsa and Castaneda staining.
Culture of Rickettsia mooseri / Rickettsia typhi
Rickettsia fails to grow in cell-free media but can be cultured in the cell line, chick embryo, and animal inoculation. Cell lines such as HeLa, Hep 2, are used to maintain culture for primary isolation. Culture in yolk sack done for vaccine preparation. Animal inoculation is done in guinea pigs and mice.
The optimum temperature for the culture of Rickettsia mooseri / Rickettsia typhi is around 32-35°C.
Neill-Mooser reaction / Tunica reaction
Differentiates Rickettsia prowazeki and Rickettsia typhi
Male guinea pigs inoculate intraperitoneally with blood from typhus case
fever + scrotal inflammation (positive for Rickettsia typhi and negative for Rickettsia prowazeki)