Rapid culture-independent techniques for quantitation of Chlamydia trachomatis elementary bodies

Quantification of Chlamydia trachomatis elementary bodies in urine by ligase chain reaction

Modification of the standard Chlamydia trachomatis ligase chain reaction (LCR) detection assay resulted in a quantitative test. Sample rates from C. trachomatis standards ranging from 32 to 1,048,576 elementary bodies (EB)/ml of urine exhibited a linear correlation with concentration. Quantitative LCR (qLCR) was used to measure the number of EB per milliliter in 158 urine samples from women in Madagascar that tested positive for C. trachomatis by the standard LCR detection assay. C. trachomatis concentrations displayed an apparent bimodal distribution, with approximately one-third of samples (37%) in a peak ranging from 32 to 1,015 EB/ml (median = 297 EB/ml) and the remainder (63%) in a grouping with relatively higher concentrations, ranging from 1,086 to 218,670 EB/ml (median = 7,389 EB/ml). qLCR will be useful for studies of chlamydial infection aimed at understanding the associations of organism burden with clinical manifestations and transmission.

Genome size and genetic map of Cowdria ruminantium

Cowdria ruminantium is the cause of a serious tick-borne disease of domestic ruminants, known as heartwater or cowdriosis. The organism belongs to the tribe Ehrlichieae:, which contains obligate intracellular pathogens, causing several important animal and human diseases. Although a few C. ruminantium genes have been cloned and sequenced, very little is known about the size, gross structure and organization of the genome. This paper presents a complete physical map and a preliminary genetic map for C. ruminantium. Chromosomal C. ruminantium DNA was examined by PFGE and Southern hybridization. PFGE analysis revealed that C. ruminantium has a circular chromosome approximately 1576 kb in size. A physical map was derived by combining the results of PFGE analysis of DNA fragments resulting from digestion of the whole genome with KSP:I, RSR:II and SMA:I and Southern hybridization analysis with a series of gene probes and isolated macrorestriction fragments. A genetic map for C. ruminantium with a mean resolution of 290 kb was established, the first for a member of the Ehrlichieae: A total of nine genes or cloned C. ruminantium DNA fragments were mapped to specific KSP:I, RSR:II and SMA:I fragments, including the major antigenic protein gene, map-1.

Macrorestriction fragment profiles reveal genetic variation of Cowdria ruminantium isolates

Macrorestriction profile analysis by pulsed-field gel electrophoresis (PFGE) was used to distinguish between seven isolates of Cowdria ruminantium from geographically different areas. Characteristic profiles were generated for each isolate by using the restriction endonucleases KspI, SalI, and SmaI with chromosomal sizes ranging between 1,546 and 1,692 kb. Statistical analysis of the macrorestriction profiles indicated that all the isolates were distinct from each other; these data contribute to a better understanding of the epidemiology of this pathogen and may be exploited for the identification of genotype-specific DNA probes.

Immunisation of sheep against heartwater with inactivated Cowdria ruminantium

The immunisation of sheep with inactivated Cowdria ruminantium organisms (the causative agent of heartwater) emulsified in Freund's adjuvant induced protective immunity against a homologous challenge with virulent cell culture-derived C ruminantium organisms. This protective immunity was associated with the development of high titres of C ruminantium-specific antibodies, a low level of rickettsiosis in brain endothelium and no mortalities. In contrast, when unimmunised sheep were challenged, they developed higher levels of rickettsiosis in brain endothelium, and some of them died. This method of immunisation against heartwater has the potential to replace the infection and treatment method that is in current use.

Binding of the glycan of the major outer membrane protein of Chlamydia trachomatis to HeLa cells

Recent studies have shown that the major outer membrane protein (MOMP) of Chlamydia trachomatis is glycosylated. The glycan of the MOMP of C. trachomatis serovar L2 was separated from the glycoprotein with N-glycanase, reduced with tritiated NaBH4, and tested for its ability to interact with HeLa cells. The [3H]glycan was shown to attach readily to HeLa cells at 25 or 37 degrees C. This process was slower at 4 degrees C. Competition for possibly similar receptor sites on HeLa cells between the glycan and a sugar, an aminosaccharide, or elementary bodies (EBs) was then studied. D-Galactose, D-mannose, or N-acetylglucosamine was shown to reduce the attachment of the glycan to HeLa cells at concentrations of 0.1 to 0.5 M. Sedoheptulose, D-fructose, or sialic acid did not inhibit the binding of glycan to HeLa cells. The presence of at least 100 native or UV-inactivated EBs per HeLa cell interfered with the glycan's ability to bind to HeLa cells. Heat-inactivated EBs did not compete with the glycan for binding. In the reverse situation, nonradiolabeled glycan prevented the EBs from infecting and forming inclusions in HeLa cells. Incubation of [3H]glycan with rabbit immune serum prepared against antigens of whole EB and the MOMP inhibited attachment. In contrast, incubation of glycan with mouse monoclonal antibodies against the protein portion of the MOMP or the chlamydial lipopolysaccharide did not inhibit attachment. These results suggest that the glycan portion of the MOMP is involved in the attachment process of C. trachomatis organisms to HeLa cells.

An immunoblotting diagnostic assay for heartwater based on the immunodominant 32-kilodalton protein of Cowdria ruminantium detects false positives in field sera

Heartwater, a major constraint to improved livestock production in Zimbabwe, threatens to invade areas which have been previously unaffected. To monitor its spread in Zimbabwe, an immunoblotting diagnostic assay based on the responses of animals to the immunodominant, conserved 32-kDa protein of Cowdria ruminantium was evaluated. In this assay, no false reactions were detected with sera known to be positive and negative, but sera from some cattle, sheep, and goats from heartwater-free areas of Zimbabwe reacted strongly with the 32-kDa protein, suggesting that either these animals had previous exposure to heartwater or they were false positives. To investigate the possibility of previous exposure to heartwater, 11 immunoblot-positive and 6 immunoblot-negative sheep from heartwater-free areas of Zimbabwe were compared regarding their susceptibilities to challenge with C. ruminantium. Prior to challenge, C. ruminantium could not be detected in any sheep by transmission to Amblyomma hebraeum ticks or by the polymerase chain reaction (PCR) conducted with plasma samples. All sheep were equally susceptible to the challenge, and infection was confirmed by brain biopsy, necropsy, PCR, and transmission of C. ruminantium to ticks. Our data suggest that the immunoblot-positive reactions of sera from heartwater-free areas were due not to previous C. ruminantium infection but rather to antigenic cross-reactivity between C. ruminantium and another agent(s) such as Ehrlichia species. In conclusion, the immunodominant 32-kDa protein is not antigenically specific to C. ruminantium and its use in serological diagnosis of heartwater requires reevaluation.

The sequence of the gene encoding elongation factor Tu from Chlamydia trachomatis compared with those of other organisms

Nucleotide (nt) sequences encoding the elongation factor Tu (EF-Tu), tRNA(Thr) and tRNA(Trp) from Chlamydia trachomatis have been determined. The environment of the EF-Tu-encoding gene (tuf), between two tRNA gene sequences, suggests that it is part of a tufB locus. The nt sequence and the deduced amino acid (aa) sequence were aligned with comparable sequences from other organisms and the resulting data bases were used to infer phylogenies. Phylogenetic trees based on aa sequences and nt sequences are similar, but not completely congruent with rRNA gene-based phylogenies. Both the nt and aa sequence trees concur on the early divergence of Thermotoga and Chlamydia from the bacterial root. The aa alignment highlights the presence of four unique Cys residues in the chlamydial sequence which are found at strictly conserved positions in other sequences. Further peculiarities of the chlamydial and eubacterial sequences have been mapped to the X-ray crystallographic structure of the protein.