Surface proteome analysis and characterization of surface cell antigen (Sca) or autotransporter family of Rickettsia typhi.

Surface proteins of the obligate intracellular bacterium Rickettsia typhi, the agent of murine or endemic typhus fever, comprise an important interface for host-pathogen interactions including adherence, invasion and survival in the host cytoplasm. In this report, we present analyses of the surface exposed proteins of R. typhi based on a suite of predictive algorithms complemented by experimental surface-labeling with thiol-cleavable sulfo-NHS-SS-biotin and identification of labeled peptides by LC MS/MS. Further, we focus on proteins belonging to the surface cell antigen (Sca) autotransporter (AT) family which are known to be involved in rickettsial infection of mammalian cells. Each species of Rickettsia has a different complement of sca genes in various states; R. typhi, has genes sca1 thru sca5. In silico analyses indicate divergence of the Sca paralogs across the four Rickettsia groups and concur with previous evidence of positive selection. Transcripts for each sca were detected during infection of L929 cells and four of the five Sca proteins were detected in the surface proteome analysis. We observed that each R. typhi Sca protein is expressed during in vitro infections and selected Sca proteins were expressed during in vivo infections. Using biotin-affinity pull down assays, negative staining electron microscopy, and flow cytometry, we demonstrate that the Sca proteins in R. typhi are localized to the surface of the bacteria. All Scas were detected during infection of L929 cells by immunogold electron microscopy. Immunofluorescence assays demonstrate that Scas 1-3 and 5 are expressed in the spleens of infected Sprague-Dawley rats and Scas 3, 4 and 5 are expressed in cat fleas (Ctenocephalides felis). Sca proteins may be crucial in the recognition and invasion of different host cell types. In short, continuous expression of all Scas may ensure that rickettsiae are primed i) to infect mammalian cells should the flea bite a host, ii) to remain infectious when extracellular and iii) to infect the flea midgut when ingested with a blood meal. Each Sca protein may be important for survival of R. typhi and the lack of host restricted expression may indicate a strategy of preparedness for infection of a new host.

Structural features of lipopolysaccharide from Rickettsia typhi: the causative agent of endemic typhus.

Rickettsia typhi causes endemic typhus, a relatively mild, acute febrile illness characterized by headache and macular rash. It is maintained in rodents and transmitted to humans by flea Xenopsylla cheopis. R. typhi contains a lipopolysaccharide thought to display a noticeable antigenic activity. We examined its structural features and it appears that the O-specific chain of the R. typhi LPS is composed mainly of the alternating Glc and QuiNAc residues linked by 1-->4 bonds.

Clinical and laboratory features of murine typhus in south Texas, 1980 through 1987.

OBJECTIVE: --The clinical and laboratory features of patients with murine typhus have not been extensively reviewed since 1946. We have updated these findings in patients from south Texas who were examined by modern clinical and laboratory methods from 1980 through 1987. DESIGN: --Patients were identified by serological methods in this case series, and clinical, epidemiologic, laboratory, and therapeutic data were compiled and analyzed. SETTING: --The majority of patients (77 of 80) were identified in a primary care community hospital setting; the remainder (3 of 80) were ambulatory hospital outpatients. PATIENTS: --From 1980 through 1987, a total of 345 patients were diagnosed with murine typhus; 90 of these patients were seen at four hospitals in south Texas; of these, 80 had clinical and laboratory data available for review. MAIN OUTCOME MEASURES: --The frequency of common clinical manifestations (eg, headache, fever, and rash) and laboratory findings (eg, leukocyte and platelet counts and serum chemistry abnormalities) of patients with infectious diseases was tabulated. Clinical severity was semiquantitatively assessed and was correlated with clinical, laboratory, and therapeutic results. RESULTS: --Most cases (69%) occurred from April through August. Rash occurred in 54%; the triad of fever, headache, and rash was observed in only 12.5% of patients when first examined by a physician; respiratory and gastrointestinal symptoms were also frequent. Multiple organ involvement was documented by frequent abnormal laboratory findings of the hematologic, respiratory, hepatic, and renal systems. Disease severity was related to older patient age, the presence of renal dysfunction, leukocytosis, and hypoalbuminemia, and previous therapy with sulfa antibiotics. CONCLUSIONS: --Infection by Rickettsia typhi causes a systemic illness with clinical and laboratory abnormalities not previously recognized or described. Early clinical diagnosis and treatment are needed to avoid undue morbidity and mortality.