The Causitive Agent of Rocky Mountain Spotted Fever Essay -- Biology M

The Causitive Agent of Rocky Mountain Spotted Fever The Bacteria Rickettsia rickettsii is the small, aerobic gram-negative bacterium that is the cause Rocky Mountain spotted fever in humans (and other vertebrates). They are obligate, intracellular bacteria that range in size form 0.2x0.5  µm to 0.3x2.0 µm. Rickettsia belong to the phylum alpha-protobacteria, which are capable of growing in low levels of nutrients, and have a long generation time relative to other gram negative bacteria such as Escherichia coli. In humans rickettsiae preferentially reside in the nucleus or cytoplasm of cells lining small to medium size blood vessels. Rickettsia enter host cell by inducing phagocytosis, then immediately escape the phagosome to grow and reproduce within the cytoplasm (or nucleus)of the host cell. The host cell will normally lyse eventually, causing the release of new organisms. The host cell is also harmed by the toxic effect of the cell wall. (CDC) Van Kirk et al have done studies showing that actin-based motility (ABM) is a mechanism for intercellular spread. R. rickettsii is the only Rickettsia species that utilizes ABM. Findings suggest that ABM is a major factor in causing infection; after a host cell becomes infected the polymerization of the actin of the host cell forms a filamentous actin comet tail. The actin tail aids the pathogen in moving through the cytosol and into membrane protrusions of the host cell, where it can be engulfed by neighboring cells and can initiate a new infectious cycle. The Vector Rocky Mountain spotted fever (RMSF) is classified as a zoonosis (diseases of animals that can be transmitted to humans), and requires a vector for transmission. The vectors (and reservoirs) for RMSF are tic... ...G. Marshall, Anita M Kelsey, MD. â€Å"What’s Your Diagnosis?† Consultant August 1996:1729-1735 Niebylski, Mark L., Mort G. Peacock, and Tom G. Schwan. â€Å"Lethal Effect of Rickettsia rickettsii on Its Tick Vector (Dermacentor andersoni)† Applied and Environmental Microbiology Feb 1999: p 773-338. Rahman, M. Sayeedur, Jason A. Simser, Kein R. Macaluso, and Abdu F. Azad. â€Å"Molecular and Funcional Analysis of the lepB Gene, Encoding a Type I Signal Peptidase from Rickettsia rickettsii and Rickettsia typhi.† Journal of Bacteriology August 2003 (2003 American Society for Microbiology):4578-4584. Van kirk, Levi S., Stanley F. Hayes, and Robert A. Heinzen. â€Å"Ultrastructure of Rickettsia rickettsii Actin Tails and Localization of Cytoskeletal Proteins.† Infection and Immunity (August 2000). Abstract. 16 September 2004. .