RNA-directed molecular hybridization screening: evidence for inapparent chlamydial infection

Chlamydia and chronic arthritis

Certain bacterial infections have been demonstrated to be causative of reactive arthritis. The most common bacterial trigger of reactive arthritis is Chlamydia trachomatis. Chlamydia pneumoniae is another known cause, albeit far less frequently. Although Chlamydia-induced reactive arthritis will often spontaneously remit, approximately 30% of patients will develop a chronic course. Modern medicine has provided rather remarkable advances in our understanding of the chlamydiae, as these organisms relate to chronic arthritis and the delicate balance between host and pathogen. C. trachomatis and C. pneumoniae both have a remarkable ability to disseminate from the initial site of infection and establish persistently viable organisms in distant organ sites, namely the synovial tissue. How these persistent chlamydiae contribute to disease maintenance remains to be fully established, but recent data demonstrating that long-term combination antimicrobial treatment can not only ameliorate the symptoms but eradicate the persistent infection suggest that these chronically infecting chlamydiae are indeed a driving force behind the chronic inflammation. We are beginning to learn that this all appears possible even after an asymptomatic initial chlamydial infection. Both C. trachomatis and C. pneumoniae are a clear cause of chronic arthritis in the setting of reactive arthritis; the possibility remains that these same organisms are culpable in other forms of chronic arthritis as well.

Molecular Diagnostics and Comparative Genomics in Clinical Microbiology

Initially, the availability of molecular diagnostics was considered a panacea, but replacement of conventional tests for detection and identification of microorganisms by molecular procedures eventually gathered momentum. This chapter describes current state-of-the-art molecular diagnostics and comparative genomics in medical microbiology to provide an understanding of infectious disease over the coming years. Nucleic acid-based tests are being introduced with increasing speed into routine clinical microbiology laboratories. Some of the problems remaining to be solved prior to general acceptance of nucleic acid-mediated detection and identification of microbial pathogens are reviewed. Historic objections are slowly being taken apart, and an accelerated introduction of molecular diagnostics is being pursued in many cases. Clear improvement in clinical testing is achieved by introducing molecular tests. Therefore, swift introduction of such tests into clinical practice is important to be pursued. Several PCR tests show increased sensitivity, excellent specificity, and cost effectiveness highlighting the success of the novel applications in the field of bacterial infections. Finally, some of the problems remaining to be solved prior to general acceptation of nucleic acid-mediated detection and identification of microbial pathogens are also reviewed.

Conjunctival chlamydial 16S ribosomal RNA expression in trachoma: is chlamydial metabolic activity required for disease to develop?

BACKGROUND

Nucleic acid amplification testing frequently detects conjunctival Chlamydia trachomatis infection in subjects without clinical signs of trachoma. It is unclear whether such subjects are actually infected. We measured chlamydial 16S ribosomal RNA (rRNA) expression, a marker of chlamydial metabolic activity, in comparison with the quantitation of a chlamydial DNA target in subjects exposed to trachoma.

METHODS

Subjects from 2 Gambian villages where trachoma was endemic were examined. Conjunctival samples were tested for the presence of C. trachomatis DNA using a quantitative real-time polymerase chain reaction (PCR) assay for the omp1 gene and for the expression of C. trachomatis 16S rRNA using a 1-step, real-time reverse-transcriptase PCR assay.

RESULTS

A total of 248 people were examined. The prevalence of clinically active trachoma was 16.9%. C. trachomatis was detected in 19.8% and 6.8% of subjects by the omp1 and 16S rRNA assays, respectively. For subjects with positive results for both tests, the number of copies of 16S rRNA was approximately 100-fold greater than the number of copies of the omp1 gene. In samples from subjects in whom the omp1 gene was detected in the absence of 16S rRNA, typically only a few copies of omp1 were present. The expression of 16S rRNA was strongly associated with the presence of clinical signs of active trachoma.

CONCLUSIONS

The use of 16S rRNA expression for the detection of chlamydial metabolic activity appears to usefully discriminate established infections from the inoculation of the conjunctiva with dead or subviable organisms, which probably occurs frequently in settings in which trachoma is endemic. The data support conclusions from primate challenge studies that live Chlamydiae species or antigens derived from them are needed to provoke the clinical signs of disease.

The intracellular life of chlamydiae

The ability to cause persistent infection is one of the major characteristics of all chlamydial species in their appropriate hosts. Persistent infection with Chlamydia trachomatis and Chlamydia pneumoniae has been implicated in the pathogenesis of many chronic diseases, some initially not thought to be infectious, including pelvic inflammatory disease, arthritis, asthma, and atherosclerosis. Chlamydiae have a unique developmental cycle with morphologically distinct infectious and reproductive forms: elementary (EB) and reticulate bodies (RB). Chlamydiae appear to circumvent the host endocytic pathway and inhabit a nonacidic vacuole that is dissociated from late endosomes and lysosomes. Chlamydiae also have been demonstrated to enter a persistent state after treatment with cytokines such as interferon-gamma (IFN-gamma), treatment with antibiotics, or restriction of certain nutrients, or to enter this state spontaneously under certain culture conditions. While the organism is in the persistent state, metabolic activity is reduced, and the organism is often refractory to antibiotic treatment. Ultrastructural analysis of IFN-gamma-treated C pneumoniae demonstrates atypical inclusions containing large reticulate-like aberrant bodies with no evidence of redifferentiation into EBs. Persistent C pneumoniae infection appears to be associated with continued expression of genes associated with DNA replication but not with those genes involved with bacterial cell division. The latter observation may explain the appearance of the large abnormal RBs seen in ultrastructural studies. Studies of the association of chlamydiae with chronic disease have been hampered by difficulties in diagnosing chronic, persistent infection with the organism, which, in turn, render determining the efficacy of antibiotic therapy very difficult.

Persistence of Chlamydia trachomatis infection detected by polymerase chain reaction in untreated patients

BACKGROUND

Prior studies have used Chlamydia trachomatis culture methods to demonstrate both persistence and spontaneous clearance of genital C trachomatis infection.

OBJECTIVE

To further assess the issue of persistence and spontaneous clearance of C trachomatis infection, untreated men and women were evaluated with repeated polymerase chain reaction (PCR) testing.

METHODS

Ninety four untreated patients with a prior positive C trachomatis PCR test returning to the Denver Metro Sexually Transmitted Disease Clinic were retested by PCR.

RESULTS

The median and range intervals from initial to follow-up testing were 9.0 (2-112) days for men and 10.0 (2-231) days for women. Repeated PCR tests were positive for 29 of 36 men (80.6%) and 45 of 58 women (77.6%). Persistent PCR positivity did not decrease with a longer testing interval. By multivariate analysis, independent predictors of a persistently positive PCR test included nonwhite ethnicity, an interval of more than 3 days since last sexual encounter before the initial test, and an initial PCR optical density value of greater than or equal to 3.0.

CONCLUSIONS

In the absence of treatment, a large majority of patients testing positive for C trachomatis by PCR are likely to remain positive for variable periods of time, increasing the risk of transmission and immune-mediated damage. A low initial optical density value and recent sexual contact may be markers for exposure that does not establish infection.

Rapid communication: Cervical Chlamydia trachomatis in women at low risk for infection

BACKGROUND

Evidence suggests that the bacterium Chlamydia trachomatis can cause asymptomatic genital infection in persons at risk for acquisition of the organism. We employed 2 independent molecular screening systems to assess such inapparent cervical chlamydial infections in low-risk female patients attending general (non-STD) clinics in 2 locations.

METHODS

Three hundred seventy-five cervical swab samples were obtained in duplicate from patients attending a general women's clinic (278 samples) and a colposcopy clinic (97 samples). One set of samples from the general clinic was screened by a highly-specific molecular hybridization system, using a probe targeting the chlamydial 16S ribosomal RNA; the other set was screened with the use of the Chlamydiazyme test. Samples from the colposcopy clinic were screened using a sensitive and specific polymerase chain reaction (PCR) assay system targeting chlamydia; the duplicates were assayed by direct fluorescent antibody assay (DFA).

RESULTS

Of the 278 patients screened by RNA-directed hybridization, 6.5% were positive for C. trachomatis, in contrast to screening of duplicate samples via Chlamydiazyme, which indicated that 3.6% were infected. PCR-based screening of the additional 97 patients gave a positivity rate of 17.5% for the organism, whereas DFA on duplicate samples from this group showed only 7.5% positive.

CONCLUSIONS

These observations suggest that the level of asymptomatic cervical C. trachomatis infection is significant even in women who are at low risk for such infections; the data also indicate that results from standard laboratory screening for chlamydia should be viewed with caution.

In situ hybridization for the detection and localization of swine Chlamydia trachomatis

Gnotobiotic piglets were inoculated intralaryngeally with swine Chlamydia trachomatis strain R33 or orally with swine C. trachmatis strain R27. Archived formalin-fixed, paraffin-embedded tissues from piglets euthanatized 4-7 days postinoculation were examined by in situ hybridization for C. trachomatis nucleic acid using a nonradioactive digoxigenin-labeled DNA probes that targeted specific ribosomal RNA or omp1 mRNA molecules of the swine C. trachomatis strains. Positive hybridization signals were detected in bronchial epithelial cells, bronchiolar epithelial cells, pneumocytes, alveolar and interstitial macrophages, and jejunal and ileal enterocytes. Chlamydia-infected cells had a strong signal that was confined to the intracytoplasmic inclusions. Positive hybridization signals were not detected in tissue sections from an uninfected control piglet or in C. psittaci-infected sheep placenta. The morphology of host cells was preserved despite the relatively high temperature required in parts of the incubation procedure. The data indicate that in situ hybridization can be used to detect swine C. trachomatis in formalin-fixed, paraffin-embedded tissue specimens.

In situ hybridisation and direct fluorescence antibodies for the detection of Chlamydia trachomatis in synovial tissue from patients with reactive arthritis

BACKGROUND

Chlamydia trachomatis is associated with Reiter's syndrome and reactive arthritis but the form in which the organism survives in synovial cells is unclear.

AIM

To compare in situ hybridisation with direct fluorescence in the detection of inapparent chlamydial infection in synovial tissue.

METHODS

Synovial tissue from four patients with reactive arthritis patients was examined using biotin labelled probes for chlamydial DNA and fluorescein isothiocyanate (FITC) labelled monoclonal antibodies against the major outer membrane protein.

RESULTS

In two of the four patients, evidence of chlamydial infections was detected by in situ hybridisation in parallel sections but not with FITC labelled monoclonal antibodies.

CONCLUSIONS

Detection of chlamydial DNA by in situ DNA hybridisation may be a better way to identify chlamydial infection in synovial tissue than phenotype targeting with FITC conjugated antibodies, which is used as a standard procedure for screening clinical specimens for chlamydia.

Detection of bacterial DNA in joint samples from patients with undifferentiated arthritis and reactive arthritis, using polymerase chain reaction with universal 16S ribosomal RNA primers

OBJECTIVE

Bacteria are considered to be important in the pathogenesis of several forms of arthritis. The goal of this study was to apply the 16S ribosomal RNA (rRNA)-polymerase chain reaction method for the detection of bacterial DNA in synovial fluid (SF) and synovial tissue (ST) from inflamed joints.

METHODS

Samples from 5 patients with septic arthritis and from 7 with osteoarthritis or arthritis secondary to joint trauma were used as controls. Samples from 6 patients with spondylarthropathy (SpA) and from 20 with undifferentiated arthritis (UA) were analyzed for the presence of bacterial DNA using universal 16S rRNA primers. Automated sequencing and comparative data analysis were performed to identify the species.

RESULTS

In the positive control group, the bacterial species cultured from the synovium could be identified in all cases. No bacterial DNA was detected in the SF and ST from patients in the negative control group. In 4 of 6 patients with SpA and 7 of 20 with UA, the analysis of joint samples revealed the presence of bacterial DNA. Sequence analysis indicated the presence of multiple species, which was confirmed by sequencing of cloned products.

CONCLUSION

When the the above techniques were used with a stringent regimen, we were able to demonstrate that it is possible to collect and analyze joint samples without contaminating bacterial DNA. The accumulation of phagocytic cells that contain bacterial DNA of various species could play a role in the pathogenesis of both SpA and UA.

Case report: in situ hybridization for detection of inapparent infection with Chlamydia trachomatis in synovial tissue of a patient with Reiter's syndrome

The authors have shown that protein antigens, RNA, and DNA from Chlamydia trachomatis are present in synovial tissues of patients with Reiter's syndrome (RS). However, those studies gave no insight into the host cell type involved or the precise tissue location of the bacteria. To address such issues, the authors developed an in situ hybridization system to detect chlamydia, and they used that system to examine synovial biopsies from a patient with RS and a patient without RS. The in situ system uses a previously described digoxigenin-labeled DNA probe that hybridizes with chlamydial 16S rRNA sequences in paraformaldehyde-fixed samples. Control studies with chlamydia-infected and uninfected HeLa cells confirmed that the in situ system is as sensitive as is direct fluorescence cytology for detection of the organism. Morphology of host and chlamydia cells is preserved after hybridization. Studies using synovial tissue from an osteoarthritis patient produced no in situ hybridization signal, but similar hybridization to tissue from a culture-/direct fluorescence cytology- negative RS patient had a strong intracellular signal for chlamydia within a subsynovial cell layer. These in situ hybridization results confirm the extensive presence of chlamydia in synovia and extend the authors' earlier observation that chlamydia RNA is present in the synovia of patients with RS. The data also confirm their electron microscopy studies, indicating that chlamydia are intracellular in synovial tissue, and they further show that infected host cells are located beneath the synovial lining.

Alteration of Chlamydia trachomatis biologic behavior in synovial membranes. Suppression of surface antigen production in reactive arthritis and Reiter's syndrome

OBJECTIVE

To investigate the biologic state of Chlamydia and its surface antigen expression in the synovial membranes of patients with Chlamydia-associated reactive arthritis/Reiter's syndrome (ReA/RS).

METHODS

Expression of chlamydial lipopolysaccharide (LPS), major outer membrane protein (MOMP), and elementary body (EB) antigens was studied by gold labeling immunoelectron microscopy on 6 synovial membrane and 2 synovial fluid (SF) pellet samples from 6 patients with Chlamydia-associated arthritis. The study findings were compared with 24-hour cultures of HeLa cells infected with Chlamydia trachomatis EB.

RESULTS

Persistent C trachomatis infection was found in all 6 synovial membrane samples from patients who had either early or chronic arthritis. The infection persisted despite antibiotic treatment, including a 1-month course of doxycycline therapy. Most persistent organisms were atypical reticulate bodies (RBs) found in both fibroblasts and macrophages. Specific, but weak, immunogold staining for all 3 antibodies was found on both intracellular RBs and extracellular EBs. In the SF samples, Chlamydia surface antigens were detected only in phagosomes containing degraded electron-dense materials.

CONCLUSION

The synovial membrane biopsies conducted in this study of Chlamydia-associated ReA/RS revealed atypical RBs with diminished MOMP and LPS expression. Such altered organisms may escape immune surveillance and contribute to disease chronicity; moreover, these organisms may be difficult to detect and treat in some ReA/RS patients.

Effects of two antibiotic regimens on course and persistence of experimental Chlamydia pneumoniae TWAR pneumonitis

We studied the effects of two antibiotic regimens on the course of Chlamydia pneumoniae infection in the lungs of Swiss Webster mice. After intranasal challenge with isolates AR-388 (1.3 x 10(7) inclusion-forming units per mouse) and AR-39 (1.5 x 10(6) inclusion-forming units per mouse), groups of animals were treated with either doxycycline (10 mg/kg of body weight once a day for 3 days), azithromycin (10 mg/kg [single dose]), or saline. Responses were assessed by the isolation of organisms in cell culture, detection of TWAR DNA in lung tissues by PCR, and lung histology. Both regimens were effective in clearing infections induced by AR-388 (P = 0.02 and 0.007 for doxycycline and azithromycin, respectively) compared with controls. TWAR DNA was detected in 77 and 25% of culture-negative lungs 2 weeks after treatment of AR-388 and AR-39 infections, respectively. Histological changes showed interstitial pneumonitis and were similar over time for all groups. Single-dose azithromycin produced drug levels in lung tissues above the MICs for the test strains for a period three times longer than that of single-dose doxycycline. We concluded that short-term antibiotic regimens were successful for the treatment of experimental TWAR pneumonitis in mice. TWAR DNA was frequently recovered from lung tissues after apparently successful treatment.

Reactivation of persistent Chlamydia trachomatis infection in cell culture

Gamma interferon induces persistent chlamydial infections in cell culture. These infections are characterized by altered morphologic and biochemical features of the pathogen. These persistent forms are abnormally large and noninfectious and undergo unusual structural and functional changes, including production of a paucity of outer envelope constituents and normal levels of the chlamydial hsp60, an immunopathological antigen. The current investigation evaluates the events that occur during reactivation of infectious Chlamydia trachomatis from persistently infected cell cultures. Transfer of persistent chlamydial organisms to gamma interferon-free medium resulted in recovery of infectivity accompanied by an increase in levels of structural membrane proteins and reorganization of aberrant organisms to morphologically typical elementary bodies. In addition, reactivation of infectious organisms from persistent chlamydiae that were maintained in culture for several weeks was demonstrated. These studies show that persistent C. trachomatis maintains viability for extended periods, illustrate the reversibility of immunologically mediated persistent infections, and characterize reactivation at the ultrastructural and biochemical levels.

Persistent chlamydiae: from cell culture to a paradigm for chlamydial pathogenesis

Chlamydiae are medically important bacteria responsible for a wide range of human infections and diseases. Repeated episodes of infection promote chronic inflammation associated with detrimental immune system-mediated pathologic changes. However, the true nature of chlamydial pathogenesis may encompass repeated infection superimposed upon persistent infection, which would allow for heightened immune reactivity. During the course of chlamydial infection, numerous host elaborated factors with inhibitory or modifying effects may cause alterations in the chlamydia-host cell relationship such that the organism is maintained in a nonproductive stage of growth. Abnormal or persistent chlamydiae have been recognized under a variety of cell culture systems. The numerous factors associated with altered growth suggest an innate flexibility in the developmental cycle of chlamydiae. This review evaluates in vitro studies of chlamydial persistence and correlates these model systems to features of natural chlamydial disease.

Intracellular location of inapparently infecting Chlamydia in synovial tissue from patients with Reiter's syndrome

Culture of Chlamydia trachomatis from synovial tissues/fluids from Reiter's syndrome (RS) patients frequently yields negative results. However, we have identified chlamydial RNA at that site in such patients, suggesting that viable organisms may be present. Here we define the cellular location of chlamydia within the synovium via in situ hybridization. Using a chlamydial ribosomal RNA-directed probe, we show that synovial tissue from culture-negative RS patients gives strong hybridization which is often localized to a subsynovial cell layer, rather than to the synovial lining; in some cases, hybridizing cells are dispersed through the synovium. All hybridization signal is located within host cells, indicating that infectious extracellular elementary bodies are rare or absent. These data confirm the extensive intracellular presence of inapparent chlamydia in the synovia of RS patients and provide some insight into the usual culture negativity of synovial tissues for the organism.

Morphologic and antigenic characterization of interferon gamma-mediated persistent Chlamydia trachomatis infection in vitro

An in vitro cell culture system was used to study the effect of interferon gamma (IFN-gamma) on Chlamydia trachomatis growth and differentiation. The effect of IFN-gamma on chlamydiae was dose-dependent. IFN-gamma at 2 ng/ml completely inhibited chlamydial growth and differentiation; however, persistent infection was established when chlamydiae were cultured with IFN-gamma at 0.2 ng/ml. Persistent infection was characterized by the development of noninfectious atypical chlamydial forms from which infectious progeny could be recovered only when IFN-gamma was removed from the culture system. Analysis of persistently infected cells by immunofluorescent microscopy and immunoblotting with specific antibodies revealed that the atypical chlamydial forms had near-normal levels of the 60-kDa heat shock protein, an immunopathologic antigen, and a paucity of the major outer membrane protein, a protective antigen. Furthermore, steady-state levels of other outer membrane constituents, such as the 60-kDa cysteine-rich outer membrane protein and lipopolysaccharide, were greatly reduced. If IFN-gamma causes similar events to occur in vivo, then persistently infected cells could augment the pathogenesis of the chronic inflammatory sequelae that follow chlamydial infection by serving as depots of antigen capable of stimulating a sustained inflammatory response.

Demonstration of chlamydial RNA and DNA during a culture-negative state

Trachoma is a common blinding disease of humans caused by ocular infections with Chlamydia trachomatis. The cynomolgus monkey is a valuable primate model for the detection, pathobiology, and treatment of this infection. We have used this model system to compare the relative ability of tissue culture, direct fluorescence cytology, a modified polymerase chain reaction, and RNA blotting to detect C. trachomatis following primary infection and reinfection over 34 weeks. Six cynomolgus monkeys were given a primary ocular chlamydia infection, and 20 weeks later they were reinoculated with the same organism. All animals showed brisk inflammatory responses to the primary infection and milder inflammatory reactions to reinfection. All four diagnostic techniques detected chlamydia at 1 week after primary infection, but both nucleic acid detection methods suggested that organisms were present longer after primary infection than did either tissue culture or direct fluorescence cytology (16 weeks for RNA blotting versus 12 weeks for tissue culture). Following reinoculation at 20 weeks, the period of C. trachomatis detection by tissue culture or direct fluorescence cytology (4 weeks) was much shorter than after primary infection. In contrast, nucleic acid detection was positive for up to 5 weeks longer than tissue culture or direct fluorescence cytology. Both polymerase chain reaction and RNA blotting, which involved no amplification step, indicated the presence of organisms during the culture-negative period. These data suggest that live chlamydiae may remain at a site of infection and produce inflammation beyond the time at which standard microbiological techniques are able to detect them.

Molecular evidence for the presence of chlamydia in the synovium of patients with Reiter's syndrome

OBJECTIVE

There is much evidence indicating that chlamydial antigens in the synovium may be critical in the pathogenesis of Reiter's syndrome (RS), but it is not known whether intact organisms are present in that tissue in any stage of the disease. The present study was undertaken to begin to address this question.

METHODS

We used a highly specific and sensitive molecular hybridization screening system which detects chlamydial RNA, to examine synovial biopsy samples from 22 patients with various arthropathies, including 9 with RS.

RESULTS

Seven of the 9 RS patients were positive for chlamydial RNA, while 3 of the 13 non-RS patients were also positive; positive results in the non-RS patients probably indicate the actual presence of the organism, since these patients had arthritis that was otherwise incompletely explained.

CONCLUSION

The detection of chlamydial RNA, in combination with previous findings of chlamydia-like particles and/or chlamydial antigens in the synovium of RS patients, suggests that whole bacterial cells are present in that tissue.

Inapparent genital infection with Chlamydia trachomatis and its potential role in the genesis of Reiters syndrome

An infectious etiology has been suggested for Reiter's syndrome (RS) because the disease has often been observed to follow episodes of urethritis or dysentery. Despite demonstrations of bacterial antigens in the synovial tissues of RS patients, it is not clear whether viable organisms are present in the synovium in any particular stage of this disease. Furthermore, it is not clear how either viable organisms or their product(s) might reach the joints. Infection with the bacterium Chlamydia trachomatis is the most common sexually transmitted disease in the United States, and as such this organism has emerged as a primary pathogen associated with RS. Previous work from our group has shown that synovial biopsy tissues from a majority of RS patients studied show significant levels of apparently intact chlamydial RNA, even when synovial or urethral cultures from the same patients are unequivocally negative for the organism. We show here that inapparent urethral infection with chlamydia occurs with high prevalence in men, and that inapparent cervical infection with the organism occurs at high prevalence in women. These data provide an important link in the relationship between initial chlamydial infection and possible subsequent genesis of RS, and they may give useful insight into mechanisms by which chlamydial infection can lead to development of this disease. Our data argue further that inapparent infection may be a significant factor in pathogenesis for all chlamydia-related diseases, and they suggest that, contrary to current ideas, C. trachomatis can generate disseminated infection.

Inapparent ocular infection by Chlamydia trachomatis in experimental and human trachoma

There is substantial indirect evidence which suggests that Chlamydia trachomatis can generate inapparent, persistent infections in human. To confirm this directly, we examined ocular chlamydial infection in both the cynomolgus monkey model of trachoma and in patient samples from a trachoma-endemic area. In monkeys, ocular infection was studied over time using direct immunofluorescence cytology (DFA) and a molecular hybridization screening system which targets chlamydial ribosomal RNA. In eleven animals infected once with B serovar, DFA and probe screening of parallel conjunctival swabs gave congruent results through day 42 post-infection. Thereafter, DFA showed clearing of chlamydia and was negative by day 70, as in previous studies. In contrast, hybridization analysis indicated a continuing presence of chlamydial RNA in all samples from all animals through the end of the experiment at day 84 post-infection. Similarly, analysis of swabs from trachoma patients showed that a number of DFA-negative samples gave clear positive signal for chlamydial RNA. Taken together these data indicate that ocular chlamydial infection persists for longer periods than previously thought, judging solely on the basis of DFA, and they support the idea that inapparent ocular chlamydial infection occurs in vivo.

Recurrent arthritis in Reiter's syndrome: a function of inapparent chlamydial infection of the synovium?

Present or prior infection with any of several common bacterial pathogens has been strongly implicated in the development of Reiter's syndrome (RS). However, because Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen in the western hemisphere, this organism has emerged as a major causative agent of the disease. An important but as yet poorly understood aspect of chlamydia-related RS is the recurrence of active arthritis in the absence of any overt infection or reinfection with the organism. In this article, a large body of published clinical and experimental observations strongly suggesting that some chlamydial infections in humans can be inapparent--not detectable by standard culture or antibody-based laboratory screening methods--is reviewed. The authors' own initial molecular genetic studies, which support that contention, are summarized. Based on these data, the argument is developed that not only does inapparent chlamydial infection occur in humans, but such infections may have significant consequences in terms of the pathogenesis of RS, including the possible causation of recurrent episodes of disease in the absence of active infection. The therapeutic implications of potential inapparent chlamydial infections as they relate to RS are discussed.