Deoxyribonucleic acid hybridization analysis for the detection of urogenital Chlamydia trachomatis infections in women

Detection of Neisseria gonorrhoeae and Chlamydia trachomatis colonization of the gravid cervix

OBJECTIVES

The aims of the study were to determine whether a Gram stain of cervical mucus can accurately rule out infection with Neisseria gonorrhoeae or Chlamydia trachomatis and to compare a diagnostic test that is based on the polymerase chain reaction with a deoxyribonucleic acid probe in the detection of these organisms.

STUDY DESIGN

Gravid patients were screened for N gonorrhoeae and C trachomatis with a deoxyribonucleic acid probe, Gram stain, and analysis with the polymerase chain reaction. A normal, noninfected sample was defined by <10 polymorphonuclear leukocytes per high-power field on the Gram stain. Standard statistical methods were used to compare results of the Gram stain and the deoxyribonucleic acid probe, as well as to compare results of deoxyribonucleic acid probe hybridization and polymerase chain reaction analysis. A P value of <.05 was considered statistically significant.

RESULTS

Patient enrollment totaled 519. The prevalence of infection as determined by deoxyribonucleic acid probe hybridization was 1.4% for N gonorrhoeae (7/518) and 6.8% for C trachomatis (35/518). The cervical Gram stain predicted the absence of infection in 17% (90/518) of patients, with a negative predictive value of 99% for N gonorrhoeae and 97% for C trachomatis. African American race, age <20 years, and unmarried status were all predictors of the presence of C trachomatis or N gonorrhoeae cervicitis. For the patients who lacked these risk factors (n = 74), the Gram stain had 100% negative predictive value. Analysis with the polymerase chain reaction detected 8 additional patients with C trachomatis and 105 additional patients with N gonorrhoeae, in comparison with deoxyribonucleic acid probe hybridization.

CONCLUSION

The cervical Gram stain can accurately predict the absence of N gonorrhoeae and C trachomatis in gravid women. Analysis with the polymerase chain reaction indicates that N gonorrhoeae and C trachomatis are significantly more prevalent in this population than previously reported.

Detection of Chlamydia trachomatis deoxyribonucleic acid in monkey models (Macaca nemestrina) of salpingitis by in situ hybridization: implications for pathogenesis

OBJECTIVE

Our purpose was to determine whether Chlamydia trachomatis persists in tubal tissues from monkey pocket models of chlamydial salpingitis and tubal infertility and to relate its presence to disease progression and histopathologic mechanisms.

STUDY DESIGN

In situ hybridization was used to detect Chlamydia deoxyribonucleic acid in a monkey pocket model of salpingitis and in the direct tubal inoculation monkey model of tubal infertility. Results were correlated with culture and immunocytochemistry results and histopathologic characteristics.

RESULTS

Chlamydia deoxyribonucleic acid was detected in the mucosa, submucosa, and deep tissues in the pocket model. In addition, it was present in peritubal adhesions from the direct inoculation model. Deoxyribonucleic acid was found at sites of inflammation and when culture and immunocytochemistry studies were negative.

CONCLUSION

The presence of Chlamydia trachomatis deoxyribonucleic acid at sites of inflammation and tissue damage in monkey models of chlamydial salpingitis and tubal infertility suggests that Chlamydia persists and may be directly involved in the stimulation of the immune-mediated tissue destruction associated with Chlamydia trachomatis infections.

Accuracy of two enzyme immunoassays and cell culture in the detection of Chlamydia trachomatis in low and high risk populations in Senegal

Two enzyme immunoassays (EIAs), Chlamydiazyme (CZ; Abbott Laboratories) and Pathfinder (PF; Kallestadt), were compared with a cell culture technique in the detection of cervical Chlamydia trachomatis infection in 670 women in urban settings in Senegal (377 pregnant women and 293 prostitutes). Positive CZ and positive PF specimens were tested a second time using a monoclonal antibody blocking technique. True positive specimens were defined as those positive on culture or positive on EIA with confirmation of the result after blocking. Using this definition, the prevalence of genital chlamydial infection was 14.6% and 14.3% in pregnant women and prostitutes respectively. An important difference between the two populations was that the pregnant women were younger than the prostitutes, which might explain the fact that the prevalence of infection among the pregnant women was as high as that among the prostitutes, although the age-adjusted prevalence was higher among prostitutes than among pregnant women. The chlamydial detection rates of cell culture, CZ and PF were 62% (26/42), 69% (29/42) and 86% (36/42) respectively in prostitutes and 76% (42/55), 40% (22/55) and 53% (29/55) respectively in pregnant women. Agreement between the tests was 89%, 85% and 88% for culture/CZ, culture/PF and CZ/PF respectively. However, when data were adjusted for chance agreement, kappa coefficients were 0.40 for culture/CZ, 0.34 for culture/PF and 0.48 for CZ/PF. These results indicate that the accuracy of the EIAs and cell culture may vary greatly in different populations: both EIAs showed a distinctly higher detection rate than culture in prostitutes and a significantly lower detection rate in pregnant women.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of a DNA probe of plasmid origin for the detection of Chlamydia trachomatis in cultures and clinical specimens

This study evaluates five cryptic plasmid-derived DNA probes in a 4-h slot-blot hybridization assay for the detection of Chlamydia trachomatis in cultures and clinical specimens. The probes, consisting of either the entire cloned 7.5 kbp cryptic plasmid pSE8 or one of four Hin dIII/Eco RI fragments measuring 710, 1055, 710, and 500 bp, respectively, were labelled with Photoprobe biotin. The probe was detected using a streptavidin-alkaline phosphatase conjugate followed by addition of BCIP and NBT. The sensitivity of the assay, using 25 ng of probe DNA, ranged from 50 pg (with the entire plasmid as probe) to 5 ng (with the 500 bp fragment as probe). A total of 103 reference strains of Chlamydia trachomatis and other bacteria were tested for reactivity with the probes. All 18 reference strains of C. trachomatis hybridized with the probes. None of the DNA from the heterologous organisms tested was found to hybridize with any of the probes. A total of 174 samples taken from patients visiting the STD clinic at the University Hospital, University of Seville were used in the study. The overall sensitivity of the assay, using the 710 bp biotinylated probe was 94.5% compared to culture while the specificity was 97.5%. Positive and negative predictive values were 96.5% and 97.5%, respectively. It appears that the plasmid-derived probes used in this study could serve as useful tools for the rapid and specific detection of Chlamydia trachomatis in cell cultures and clinical specimens.

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

Both clinical and epidemiological data suggest that inapparent infection by Chlamydia trachomatis occurs in humans. To confirm and study such infections, we developed a hybridization screening system directed toward chlamydial ribosomal RNA (rRNA). Six restriction endonuclease fragments derived from the cloned rrnA operon of chlamydial serovar L2(434) were tested as hybridization screening probes, but only one fragment encoding the 5' portion of the 16s rRNA gene plus some upstream flanking sequence was both sensitive and highly specific in such experiments. In Northern slot blot assays, hybridization analyses with this fragment as probe routinely detected one picogram or less of chlamydial RNA when that RNA was bound to membranes alone or as part of a mixture with a vast excess of mammalian RNA. The probe did not hybridize to RNA from mammalian and relevant bacterial sources but did hybridize to rRNA from B (ocular) and E (genital) serovars of C. trachomatis. Experiments using RNA from conjunctival biopsies and standard conjunctival swab samples from cynomolgus monkeys showed that the probe reliably distinguishes between known chlamydia-infected and uninfected samples. This suggests that it may be useful for clinical screening. Characterization assays for the RNA-directed probe screening system in this monkey model of trachoma provide initial molecular evidence that ocular chlamydial infection may persist longer than previously thought, based solely on direct fluorescence antibody assay (DFA) and culture analyses.

Detection of Chlamydia trachomatis endocervical infection in asymptomatic and symptomatic women: comparison of deoxyribonucleic acid probe test with tissue culture

A deoxyribonucleic acid probe assay (PACE 2, Gen-Probe, San Diego) was compared with a standard tissue culture method for detection of Chlamydia trachomatis endocervical infection in both asymptomatic and symptomatic women. The results of the probe test were expressed as a ratio of relative light units of the specimen per relative light units of the cutoff recommended by the manufacturer. Samples with sample/cutoff ratios near 1.0 were repeated until two or more consistent ratios were obtained. A total of 426 specimens were obtained, with an overall disease prevalence of 10.1%. Of the 426 specimens examined, seven (1.6%) were near the cutoff and were retested. The results of 426 samples with matching cultures indicated that the manufacturer's discrete cutoff was adequate for results determination. The deoxyribonucleic acid probe test was essentially equivalent to standard tissue culture in terms of sensitivity, specificity, and positive and negative predictive values in a low-prevalence patient population.

Chlamydiae as pathogens--an overview of diagnostic techniques, clinical features, and therapy of human infections

Chlamydiae are Gram-negative bacteria with obligate intracellular reproduction and disability to synthesize high-energy compounds such as ATP. Their cycle of development is unique among the prokaryotes: the host cells, mainly epithelial cells, are infected by so-called elementary bodies (EB) which undergo reorganization to form metabolically active reticulate bodies (RB). These RB multiply by binary fission, and after transition into infectious EB they are released within 48-72 hours. Chlamydiae cause prolonged subclinical infections of the conjunctiva, lung, cervix, and urethra. Complications in newborns are inclusion conjunctivitis, nasopharyngitis and pneumonia; in females, salpingitis, infertility, and perihepatitis; in male patients, epididymitis and prostatitis; and in both sexes, Chlamydiae-induced arthritis. Identification of the pathogenic agent confirms clinical diagnosis; tissue culture identification remains the diagnostic method of choice. Therapeutical drugs are tetracycline, erythromycin, josamycin, and in certain cases quinolone derivatives.

Detection of C trachomatis in urogenital specimens by polymerase chain reaction

OBJECTIVE

To establish a polymerase chain reaction (PCR) protocol for the detection of urogenital C trachomatis infection and to compare it with the detection in cell culture.

SPECIMENS

Urethral specimens were collected from 62 male patients and cervical specimens from 106 female patients.

SETTING

Department of Dermatology and Venereology, Ruprecht-Karls-Universität, Heidelberg.

METHODS

Urogenital specimens were simply boiled for 15 minutes and subsequently subjected to amplification without prior extraction of nucleic acid. The DNA sequence selected for amplification is located in the third open reading frame of the ubiquitous C trachomatis plasmid pCTT1. The amplified products were demonstrated by agarose gel electrophoresis followed by Southern blot hybridization. In addition, specimens were investigated with cell culture.

MAIN OUTCOME MEASURES

Results of PCR and cell culture.

RESULTS

PCR detected all C trachomatis serovars relevant for urogenital infections (D-L2). Serial dilution experiments revealed that the PCR procedure was 100 fold more sensitive than cell culture. The investigation of 168 urogenital specimens showed that the PCR confirmed all 30 cell culture positive results, however, out of the 138 cell culture negative specimens 16 were positive using the PCR.

CONCLUSIONS

A substantial number of urogenital C trachomatis infections detectable by PCR may be missed by the cell culture technique.

Chlamydia trachomatis infection during pregnancy

Although transmission of Chlamydia trachomatis to infants during vaginal birth can result in conjunctivitis and pneumonitis, there is uncertainty about other adverse effects of chlamydial infection during pregnancy. There is some evidence that it may contribute to adverse complications such as premature rupture of membranes, preterm labor and birth, low birth weight, and still birth. Infection with C. trachomatis is also implicated in postabortal, postcesarean section, and postpartum maternal infections. Treatment of chlamydial infection during pregnancy has proved beneficial in the prevention of neonatal morbidity and is now recommended by the Centers for Disease Control.

Laboratory techniques for the diagnosis of chlamydial infections

Yolk-sac inoculation of embryonated eggs was superseded 25 years ago by the use of cell cultures (often McCoy) for the isolation of Chlamydia trachomatis. Centrifugation of specimens onto the cell monolayers was shown to increase sensitivity, but little of late has further improved sensitivity which is at least ten-fold greater than that of eggs. However, culture is slow and labour intensive so that non-cultural techniques without these drawbacks have come to dominate. Direct fluorescent antibody (DFA) tests are rapid and have sensitivities that range from 70% to 100% for men and 68% to 100% for women, and specificities that range from 87% to 99% for men and 82% to 100% for women; if the tests are read by competent observers the values are at the top end of the ranges. The detection rate may be enhanced even further by relatively low-speed centrifugation of specimens before staining. Skilled reading is not a feature of enzyme immunoassays (EIAs) which according to the literature have sensitivities that range from 62% to 97% for men and 64% to 100% for women, and specificities that range from 92% to 100% for men and 89% to 100% for women. However, comparison against poor reference tests is responsible for most of the higher values and the clinician should not be misled into believing that EIAs have excellent sensitivity; the lower values in the ranges are closer to reality. Furthermore, EIAs that are being designed for use by general practitioners should be regarded with the greatest caution since lack of sensitivity means that chlamydia-positive patients will go undetected. The polymerase chain reaction (PCR) is not bedevilled by insensitivity but it is no more sensitive than the most sensitive cell culture or DFA tests. PCR is unsuitable for routine diagnosis but has a place as a research tool. For men, examination of "first-catch" urine samples by the best of the non-cultural procedures provides an acceptable non-invasive approach to diagnosis; for women, the value of examining urine may be less, but needs to be thoroughly tested. However, there is little doubt that a Cytobrush used to obtain cervical specimens holds no practical advantage over a swab. Serological tests are reliant on the provision of paired sera for making a diagnosis; high antibody titres in single sera may be suggestive of an aetiological association in deep-seated chlamydial infections (epididymitis, arthritis, salpingitis, etc), but unequivocal interpretation is unusual, particularly in an individual case, since the distinction between a current and past infection is problematical.

Intraamniotic detection of Chlamydia trachomatis deoxyribonucleic acid sequences by polymerase chain reaction

The presence of Chlamydia trachomatis in cervicovaginal cells and amniotic fluid of pregnant women was examined by culture and by polymerase chain reaction deoxyribonucleic acid amplification methods. Chlamydial deoxyribonucleic acid sequences were found in nine of 31 (29.0%) cervicovaginal cell specimens, five of which also were positive by culture method. Amniotic fluid specimens from two of the nine (22.2%) cervicovaginal chlamydial deoxyribonucleic acid-positive women and none from the remaining 22 cervicovaginal chlamydial deoxyribonucleic acid-negative women were found to contain chlamydial deoxyribonucleic acid. The results underscore the significance and frequency of intraamniotic chlamydial infection in women with urogenital chlamydial infections.

Detection of Chlamydia trachomatis by the polymerase chain reaction in swabs and urine from men with non-gonococcal urethritis

A polymerase chain reaction (PCR) was developed for Chlamydia trachomatis in which a 380 base pair DNA fragment was amplified. Amplification occurred with the DNA from the 15 serovars but not with that from other Chlamydia spp or with DNA from a variety of other organisms. Chlamydial DNA (10(-16) g) could be detected and the PCR seemed to be able to detect single organisms. Urethral swabs were obtained from 37 men with acute non-gonococcal urethritis (NGU), 18 (49%) of whom were positive for C trachomatis by MicroTrak. As a result of clinical re-examinations 65 urethral swabs were available for analysis by the PCR. In comparison with MicroTrak, PCR had a sensitivity of 95%, a specificity of 94%, a positive predictive value of 86% and a negative predictive value of 98%. The PCR was apparently less sensitive (82%) in tests on urine samples. Overall, however, values of sensitivity and specificity of the PCR compared favourably with those of MicroTrak. The PCR for C trachomatis is likely to be a valuable technique for research, but problems of DNA contamination suggest that it should not be recommended for routine diagnosis.

Comparison of three new nonculture tests in the diagnosis of Chlamydia genital infections

This study compares three new rapid nonculture tests to cell culture with passage for the diagnosis of Chlamydia genital infections in sexually active adolescent and young adult females. Two hundred consecutive patients having a pelvic examination had cervical samples taken for the following: Papanicolaou smear, gonorrhea culture, Chlamydia cell culture, direct fluorescent antibody (DFA; Difco), isotopic DNA probe (Gen-Probe), and enzyme immunoassay (EIA; IDEIA III, Novo BioLabs). After resolution of discrepant results, 25 of the specimens were judged to be positive. The DFA identified 17 of the 25, with 3 false-positive results; the DNA probe identified 20 of the 25, with no false positive results; and the EIA identified 22 of the 25, with one false-positive result. The sensitivities, specificities, and positive and negative predictive values, respectively, were DFA, 68%, 98.2%, 85%, 95.5%; DNA probe, 80%, 100%, 100%, 97.2%; and EIA, 88%, 99.4%, 95.6%, 98.3%. These new rapid nonculture tests are comparable and relatively reliable, with trends favoring the EIA and the DNA probe. Further studies with larger samples are needed to determine their clinical utility.

The detection of Gardnerella vaginalis DNA sequences in uncultured clinical specimens with cloned G. vaginalis DNA as probes

Cloned Gardnerella vaginalis DNA were selected from a plasmid DNA library constructed with partially restriction endonuclease Hind III-digested genomic DNA of G. vaginalis to serve as DNA probe in detecting G. vaginalis. The level of detection was determined to be approximately 10,000 cells by slot-blot DNA hybridization. This probe DNA will not cross-hybridize with DNA of a number of non-Gardnerella micro-organisms commonly found in female genital tract. The DNA probe-based hybridization test may become a useful tool for the identification of G. vaginalis in uncultured clinical specimens.

Detection of plasmid DNA from all Chlamydia trachomatis serovars with a two-step polymerase chain reaction

A polymerase chain reaction was used to amplify a 137-base-pair sequence of DNA from a Chlamydia trachomatis plasmid. Various parameters of the polymerase chain reaction were explored, and it was found that two short steps per reaction cycle were sufficient to achieve 10(12)-fold amplification in less than 1 h. By use of this procedure, 10(-18) g of a sequence of plasmid DNA, representing the amount of that sequence found in one C. trachomatis bacterium, was amplified to the point where it was clearly visible on an ethidium bromide-stained polyacrylamide gel under UV light. DNA from intact cells from each of the 15 serovars of C. trachomatis could also be amplified for visualization. With this procedure, the presence or absence of C. trachomatis DNA in a sample could be established in less than 1.5 h. The speed and extreme sensitivity of this detection procedure may make it a useful method for the detection of C. trachomatis, and similar techniques should be possible for any type of bacteria.

Molecular techniques for the detection of Chlamydia trachomatis

A DNA probe assay (PACE; Gen-Probe, San Diego, Calif.) was compared with a culture reference method for the detection of Chlamydia trachomatis. Using stock isolates of each of the 15 serovars (A to K, Ba, L1, L2, and L3) of C. trachomatis, the lower limit of sensitivity for the DNA probe ranged between 1,086 inclusion-forming units (IFU) for serovar E (Bour) to 2,930 IFU for serovar L1 (440), with the only exception being serovar C (TW-3), with which 99 IFU was detected. There was no cross-reactivity with Chlamydia psittaci (Texas turkey) and Chlamydia pneumoniae (TWAR-183). Bacterial and fungal isolates representing 14 species of normal vaginal flora as well as Neisseria gonorrhoeae gave negative results with the DNA probe when tested at a level of 1.5 X 10(7) CFU/ml. In addition, the DNA probe, a direct fluorescent-antibody stain (DFA) (MicroTrak; Syva Corp., Palo Alto, Calif.), and an enzyme-linked immunosorbent assay (Chlamydiazyme; Abbott Laboratories, North Chicago, Ill.) were compared with culture for the detection of C. trachomatis, using 196 clinical cervical samples. Of the 196 samples, 20 (10%) were culture positive. Of the 176 culture-negative samples, 1 was not evaluated by DNA probe and 4, because of a lack of cellular material, were not evaluated by DFA. The sensitivities of the DNA probe, DFA, and enzyme-linked immunosorbent assay were 60, 75, and 85%, respectively, and specificities were 95, 99, and 97%, respectively. Of the false-positive direct results, there was only one specimen with which more than one direct method was positive, and with this specimen all three direct methods were positive. The majority of false-negative results by the direct methods were from specimens which by the culture method gave <100 IFU per culture.

Evaluation of a radioactive rRNA:cDNA-hybridisation assay for the direct detection of Chlamydia trachomatis in urogenital specimens

A radioactive cDNA probe complementary to chlamydial ribosomal RNA was used to detect C trachomatis in urogenital specimens. Of 37 specimens positive with cell culture 31 were confirmed by the rRNA:cDNA hybridisation test, the sensitivity being 83.8%. The specificity of the hybridisation test was 94.4%, as 186 of 197 specimens that were negative by cell culture were also negative when assessed by the hybridisation method. Given a prevalence of 15.8% the predictive values for positive and negative results were 73.8% and 96.9%, respectively. In additional experiments the possible role of microorganisms added to the specimen collection medium was investigated. However, no indication for crosshybridisation was found; at high concentrations microorganisms interfered with the test procedure.

Efficacy of duplicate genital specimens and repeated testing for confirming positive results for chlamydiazyme detection of Chlamydia trachomatis antigen

In an attempt to increase Chlamydiazyme (Abbott Laboratories) detection of Chlamydia trachomatis antigen and to establish the reproducibility of positive results, we carried out an investigation into the usefulness of testing duplicate specimens, of more aggressive endocervical specimen collection by using cytobrushes instead of swabs, and of the repeated testing of both specimens from patients with one or two positive results. Duplicate endocervical (female) and urethral (male) specimens, including one swab and one cytobrush specimen from 1,331 nonpregnant women, were collected from symptomatic and asymptomatic patients. Specimens were transported and tested for C. trachomatis antigen as specified by the manufacturer. Tests on all specimens from patients with positive results were repeated. Antigen was initially detected in one or both specimens from 210 (10.7%) of 1,968 patients, and repetition of the tests confirmed its presence in 198 (10.1%) of the patients, including all 183 patients in whom it was initially detected in both specimens. Initial results from at least 8 of the 12 patients with irreproducible antigen detection were most probably falsely positive. Results from 21 (10.6%) of the 198 patients for whom antigen detection was confirmed were repeatedly positive on only one specimen (9 [4.5%] on the second of the two specimens collected). Of 115 women from whom one swab and one cytobrush sample were taken and who had repeatedly positive results, antigen was detected in 7 (6.1%) only on the swab sample and in 4 (3.5%) only on the cytobrush sample. Use of the cytobrush does not appear justified with the Chlamydiazyme assay, and collection of duplicate specimens provided only a modest increase in detection of C. trachomatis. However, repeated testing of specimens when results from only one of two specimens are positive appears to be of clinical value.

Laboratory diagnosis of human chlamydial infections

Chlamydia trachomatis is a human pathogen that causes ocular disease (trachoma and inclusion conjunctivitis), genital disease (cervicitis, urethritis, salpingitis, and lymphogranuloma venereum), and respiratory disease (infant pneumonitis). Respiratory chlamydioses also occur with infection by avian strains of C. psittaci or infection by the newly described TWAR agent. Diagnosis of most acute C. trachomatis infections relies on detection of the infecting agent by cell culture, fluorescent antibody, immunoassay, cytopathologic, or nucleic acid hybridization methods. Individual non-culture tests for C. trachomatis are less sensitive and specific than the best chlamydial cell culture system but offer the advantages of reduced technology and simple transport of clinical specimens. Currently available nonculture tests for C. trachomatis perform adequately as screening tests in populations in which the prevalence of infection is greater than 10%. A negative culture or nonculture test for C. trachomatis does not, however, exclude infection. The predictive value of a positive nonculture test may be unsatisfactory when populations of low infection prevalence are tested. Tests that detect antibody responses to chlamydial infection have limited utility in diagnosis of acute chlamydial infection because of the high prevalence of persistent antibody in healthy adults and the cross-reactivity due to infection by the highly prevalent C. trachomatis and TWAR agents. Assays for changes in antibody titer to the chlamydial genus antigen are used for the diagnosis of respiratory chlamydioses. A single serum sample that is negative for chlamydial antibody excludes the diagnosis of lymphogranuloma venereum.

Detection of Chlamydia trachomatis in culture and urogenital smears by in situ DNA hybridization using a biotinylated DNA probe

The detection of Chlamydia trachomatis by in situ DNA hybridization in urogenital smears was investigated using a commercially available biotinylated DNA probe. Intracellular staining of inclusion bodies was used as the criterion for positivity. Of 35 patients with a culture proven chlamydial infection 19 had smears in which C. trachomatis was detected by in situ DNA hybridization, indicating a sensitivity of 54%. Of 57 patients with a negative culture, two had positive smears by in situ DNA hybridization. To compare whether the criterion for positivity had influenced the sensitivity obtained with in situ DNA hybridization, 14 duplicate smears from culture positive patients were analysed with in situ DNA hybridization and immunofluorescence. Both methods detected intracellular inclusion bodies in seven of these smears, suggesting that the presence of infected cells mainly determines the sensitivity. The DNA probe did not cross-react with micro-organisms commonly found in the urogenital tract.

Detection of Chlamydia trachomatis by in situ hybridization with sulphonated total DNA

In situ nucleic acid hybridization was applied to the detection of Chlamydia trachomatis on microscope slides by use of sulphonated total DNA as a probe. Visualization of labelled DNA was obtained using a commercial enzyme-linked monoclonal antibody. A mixture of paraformaldehyde and glutaraldehyde was found to be the best fixative. With high probe concentration (10 micrograms/ml), intracellular inclusions were detected as early as 8 h after inoculating the cell culture. Extracellular elementary bodies could also be detected. Five genital specimens were tested by in situ hybridization; the results were in agreement with those observed by culture.