Shell-vial culture and real-time PCR applied to Rickettsia typhi and Rickettsia felis detection.

Murine typhus is a zoonosis transmitted by fleas, whose etiological agent is Rickettsia typhi. Rickettsia felis infection can produces similar symptoms. Both are intracellular microorganisms. Therefore, their diagnosis is difficult and their infections can be misdiagnosed. Early diagnosis prevents severity and inappropriate treatment regimens. Serology can't be applied during the early stages of infection because it requires seroconversion. Shell-vial (SV) culture assay is a powerful tool to detect Rickettsia. The aim of the study was to optimize SV using a real-time PCR as monitoring method. Moreover, the study analyzes which antibiotics are useful to isolate these microorganisms from fleas avoiding contamination by other bacteria. For the first purpose, SVs were inoculated with each microorganism. They were incubated at different temperatures and monitored by real-time PCR and classical methods (Gimenez staining and indirect immunofluorescence assay). R. typhi grew at all temperatures. R. felis grew at 28 and 32 °C. Real-time PCR was more sensitive than classical methods and it detected microorganisms much earlier. Besides, the assay sensitivity was improved by increasing the number of SV. For the second purpose, microorganisms and fleas were incubated and monitored in different concentrations of antibiotics. Gentamicin, sufamethoxazole, trimethoprim were useful for R. typhi isolation. Gentamicin, streptomycin, penicillin, and amphotericin B were useful for R. felis isolation. Finally, the optimized conditions were used to isolate R. felis from fleas collected at a veterinary clinic. R. felis was isolated at 28 and 32 °C. However, successful establishment of cultures were not possible probably due to sub-optimal conditions of samples.

Growth of typhus group and spotted fever group rickettsiae in insect cells.

To analyze the host dependency of rickettsial growth, NIAS-AeAl-2 insect cells (AeAl2) derived from mosquito were first used in this study. It was demonstrated that typhus group rickettsiae (TGR) grew well in AeAl2 cells, but spotted fever group rickettsiae (SFGR) failed. To elucidate the inhibitory process of the growth of SFGR in AeAl2 cells, the adherence and invasion were first analyzed. SFGR possessed abilities to adhere to and invade AeAl2 cells as well as TGR in contrast to their inability of the growth in the cells. Morphologically, generation of microvilli could not be observed on AeAl2 cells inoculated with either group of rickettsiae. On the contrary, Vero cells inoculated with rickettsiae generated a great number of microvilli that adhered to rickettsiae and engulfed them into the cells. The roles of rickettsial major outer membrane protein A and B (rOmpA and rOmpB) were later investigated using E. coli expressing either rOmpA or rOmpB on their surface. Bacteria expressing either one of the major outer membrane proteins of rickettsiae as well as bacteria not expressing these proteins showed adherence to and invasion of AeAl2 cells. Thus, it is yet to be elucidated whether these major outer membrane proteins have any roles in these steps.

Molecular and functional analysis of the lepB gene, encoding a type I signal peptidase from Rickettsia rickettsii and Rickettsia typhi.

The type I signal peptidase lepB genes from Rickettsia rickettsii and Rickettsia typhi, the etiologic agents of Rocky Mountain spotted fever and murine typhus, respectively, were cloned and characterized. Sequence analysis of the cloned lepB genes from R. rickettsii and R. typhi shows open reading frames of 801 and 795 nucleotides, respectively. Alignment analysis of the deduced amino acid sequences reveals the presence of highly conserved motifs that are important for the catalytic activity of bacterial type I signal peptidase. Reverse transcription-PCR and Northern blot analysis demonstrated that the lepB gene of R. rickettsii is cotranscribed in a polycistronic message with the putative nuoF (encoding NADH dehydrogenase I chain F), secF (encoding protein export membrane protein), and rnc (encoding RNase III) genes in a secF-nuoF-lepB-rnc cluster. The cloned lepB genes from R. rickettsii and R. typhi have been demonstrated to possess signal peptidase I activity in Escherichia coli preprotein processing in vivo by complementation assay.

Reverse transcriptase PCR amplification of Rickettsia typhi from infected mammalian cells and insect vectors.

We developed a reverse transcriptase PCR assay to detect expression of 120- and 17-kDa antigen genes in Rickettsia typhi. Infected Vero cell and flea RNAs were reverse transcribed by using random hexamers. The cDNA was amplified by using high concentrations of primer and template in an inexpensive, nonradioactive assay.

The in-vitro anti-rickettsial activity of macrolides.

The anti-rickettsial activity of azithromycin and clarithromycin was studied in Vero cells. The rate of rickettsial inhibition-growth caused by both macrolides was determined using rickettsial counts and ELISA. Both macrolides inhibited > 50% the growth of Rickettsia conorii and Rickettsia typhi at concentrations of 1.0 and 0.1 mg/L, respectively. The growth of Coxiella burnetii was inhibited to a rate of > or = 50% at the concentrations of 0.01 and 1.0 mg/L of azithromycin and clarithromycin, respectively.

Rickettsia mooseri infection in the fleas Leptopsylla segnis and Xenopsylla cheopis.

Detailed observations on the acquisition and propagation of experimental Rickettsia mooseri infection in two species of fleas are presented. Rickettsia mooseri infection became detectable by means of the direct fluorescent antibody test about 2 days earlier in Leptopsylla segnis than in the putative vector, Xenopsylla cheopis. By the 6th day after the infective feeding, the entire lining and the lumen of the midgut in L. segnis contained masses of rickettsiae and the agent was being passed in the feces of the flea, whereas in X. cheopis these events did not occur until the 8th day. Basic behavioral differences in the two species of flea may explain these discrepancies and also influence their ability to serve as vectors of murine typhus. As a semisessile flea and sustained feeder, L. segnis only rarely attaches to a second individual and thus has an opportunity to acquire a heavy dose of rickettsiae, if feeding on a rickettsemic host. X. cheopis, in contrast, feeds rapidly and intermittently, even on man, and generally leaves its host soon thereafter, later returning to the same or another host to feed again. While L. segnis may not be as efficient a vector as X. cheopis regarding the intramurine cycle or transmission to man of murine typhus, the dense accumulation of infective feces on certain sites on the fur of the host raises the possibility of air-borne infection to man or rodent. Infection with R. mooseri had no effect on the survival of X. cheopis and L. segnis. Furthermore, no visible cytopathological effect was found in the paraffin-embedded sections of infected fleas.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth of Rickettsia typhi in irradiated L cells enhanced by lysosomal stabilization.

The growth of some obligate intracellular parasites is contingent upon avoidance of lysosomal activation during growth in their host cells. This is accomplished by the various parasites by different mechanisms and with different degrees of efficiency. The possibility was tested that the lysosomal stabilizer cortisone acetate might protect and thus enhance the growth of Rickettsia typhi in mouse L cells irradiated 6 days earlier. Beginning 2 days before infection of the L cells with a multiplicity of 10 rickettsiae, 20 microgram of cortisone per ml was added in medium 199 containing 5% fetal calf serum. This concentration of cortisone was below the cytotoxic level, as determined by viability staining, but was sufficient to significantly alter the ratios of cellular and released acid phosphatase and beta-glucuronidase in uninfected and infected cells, as shown by spectrophotometric analysis. Rickettsial replication, measured by hemolytic activity at 96 h and confirmed by microscopic observations at earlier stages of infection, was increased by the cortisone. Cortisone concentrations of 10 or 40 microgram/ml were less effective, and cortisone was ineffective when the rickettsial multiplicity per L cell was 2 or lower. These results indicate that amounts of cortisone that increase lysosomal stabilization in L cells favor rickettsial multiplication when the multiplicity of infection is relatively high.

Biological properties of Rickettsia prowazekii strains isolated from flying squirrels.

Four strains of Rickettsia prowazekii, isolated from flying squirrels (Glaucomys volans volans) from Florida and Virginia, were compared with other strains of the typhus biotype, two previously established strains each of R. prowazekii and R. typhi and one strain of R. canada, for similarities in a number of unrelated phenotypic characteristics. R. akari served as a spotted fever biotype control. All strains produced small plaques on chicken embryo cell monolayers that were clearly recognized only after 10 days of incubation at 32 degrees C. All strains were highly susceptible to erythromycin. The Renografin density gradient centrifugation procedure of separating rickettsiae from the infected yolk sacs of surviving chicken embryos was equally satisfactory in all cases and resulted in moderate to large yields of purified rickettsiae. There was relatively small variation in specific hemolytic activity or specific CO(2) formation from glutamate. None of the strains catabolized glucose. There was some strain variation in virulence for the chicken embryo, but none of the above tests separated the three species of the typhus biotype. On the other hand, R. akari was clearly distinguished by its more rapid plaque formation and by higher resistance to erythromycin. It is concluded that by the tests conducted thus far, the biological properties of the flying squirrel strains do not differ substantially from those of other strains of the typhus biotype.

Metabolism of Rickettsia typhi and Rickettsia akari in irradiated L cells.

L cells that had been exposed to 3,000 r of (60)Co the previous day were used to study the growth and metabolism of Rickettsia typhi and R. akari. Viable (unirradiated) L cells were used to study the effect of rickettsial infection on host-cell metabolism. Monolayers were infected with a rickettsial multiplicity of 1.2 and given Eagle's minimal essential medium containing 25 mmN-2-hydroxyethylpiperazine-N'-2'-ethanesulfonic acid buffer and 10% calf serum. At various intervals, cycloheximide (2 mug/ml) was added to one set of cultures, to inhibit eukaryotic protein and deoxyribonucleic acid (DNA) metabolism; phosphate-buffered saline (PBS) was added to another set. After 1 hr, the cultures received a mixture of 15 (14)C-labeled amino acids or adenine-8-(14)C. The cultures were harvested 16 hr later and were tested for incorporation of labeled carbon into the fraction precipitated by cold trichloroacetic acid. Viable cells were exposed to thymidine-2-(14)C for 2-hr periods. Infectivity of R. typhi increased to a peak of 150 to 400 hemolytic units/culture on day 4; the titer remained approximately the same on days 5 and 6, and declined rapidly on day 7. Total amino acid incorporation was about the same in infected and uninfected cultures up to day 6, but metabolic activity was reduced to a negligible level on day 7 in infected cells. Cycloheximide-resistant activity was higher in the infected cultures, with a peak equivalent to one-half the total activity at day 4 to 5. Total as well as cycloheximide-resistant adenine incorporation was higher in the infected cells between days 3 and 5 after infection, with a peak at day 3 to 4. Somewhat similar results were obtained with R. akari, except that the cycle of infection and of cycloheximide-resistant activity proceeded and was completed more rapidly. (14)C-DNA of both rickettsiae was isolated from infected cultures that had received labeled adenine. With labeled thymidine, which was not incorporated by the rickettsiae, it was shown that R. typhi and R. akari differ considerably in their effects on the host cell. R. typhi elicited moderate inhibition, whereas R. akari infection led to a complete inhibition of thymidine incorporation by the third day, at the time of highest rickettsial activity. It is concluded that rickettsiae have the necessary enzymes for protein and nucleic acid synthesis, but, thus far, these enzymes have been activated or induced only in an intracellular environment.