Preliminary evaluation of an enzyme immunoassay test for the detection of Chlamydia trachomatis

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.

Evaluation of an enzyme immunoassay for detection of Chlamydia psittaci in vaginal secretions, placentas, and fetal tissues from aborting ewes

A commercially available enzyme immunoassay (EIA) for the detection of Chlamydia trachomatis in human urogenital and conjunctival specimens was compared with isolation in cell culture for the detection of Chlamydia psittaci in vaginal and placental swabs from aborting ewes and swabs of aborted fetal tissues. The EIA on vaginal swabs collected from 10 ewes experimentally infected with C. psittaci had a sensitivity of 85.7% and a specificity of 85.7%. Vaginal swabs collected at the time of abortion or within 3 days were the best samples for detection of chlamydial infection. The 29 vaginal swabs collected during this period from experimentally infected ewes were all strongly EIA-positive, and chlamydia were isolated from 28. The EIA on vaginal swabs from 78 field cases of abortion had a sensitivity of 78.0% and a specificity of 76.8%. The EIA on swabs of cotyledons from 65 placentas had a sensitivity of 100% and a specificity of 75.0% compared with isolation in cell culture. The EIA on 57 swabs of fetal tissues or body fluids from 10 aborted fetuses or weak lambs from experimentally infected ewes had a sensitivity of 26.6% and a specificity of 88.1% compared with isolation in cell culture. Limitations of the EIA are discussed.

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.

Chlamydia trachomatis infection in late pregnancy: a prospective study

During a 1-year period, 3309 women were screened in pregnancy for Chlamydia trachomatis infection. A cervical swab was taken and chlamydial antigen was detected, using a monoclonal antibody ELISA technique, in 198 women (6%). The prevalence of chlamydial infection was high in women under 20 years (14.5%), single women (14.2%) and black women (16.8%). Binomial regression of these data estimates a relative risk of 2.9 for women under 20 years compared with women aged 25 and over. There was an interaction between race and marital status with a high risk in single white and single asian women (2.3, 4.5 respectively) but a similar risk in black single and black married women (3.0, 4.0 respectively). Parity and social class did not effect the prevalence of antigen carriage. There was no demonstrable effect of maternal antigen carriage on outcome of pregnancy, gestation or admission to neonatal unit. Infants of 174 antigen-positive mothers were followed-up. Tissue culture for Chlamydia trachomatis was positive in 43 (24%) infants. Complications occurred in 23 (53%): 17 had conjunctivitis, three had lower respiratory tract infection and three both complications. Amongst 131 chlamydia-negative infants, complications occurred in 21 (16%). Since this infection, in infants, responds promptly to erythromycin therapy, screening and treatment in pregnancy will convey little benefit in prevention of perinatal morbidity or perinatal mortality.

Evaluation of non-radioactive in situ hybridisation method to detect Chlamydia trachomatis in cell culture

A DNA probe combined with a non-radioactive stain was used to detect inclusions of Chlamydia trachomatis in cell culture. Of 39 positive cultures detected by monoclonal antibodies in combination with direct immunofluorescence, 35 were positive by the DNA hybridisation method, the sensitivity being 89.7%. Staining with iodine showed a sensitivity of 87.2%, corresponding to 34 positive cultures. The specificity of DNA hybridisation method was 100%, as all 162 cultures that were negative by the immunofluorescence method were also negative when assessed by the DNA hybridisation method.

Detection of chlamydial inclusions in cell culture or biopsy tissue by alkaline phosphatase-anti-alkaline phosphatase staining

An immunological technique for detecting Chlamydia trachomatis and Chlamydia psittaci inclusions in infected McCoy cell cultures was developed by using a genus-specific monoclonal antibody to Chlamydia spp., rabbit anti-mouse immunoglobulin G bridging antibody, alkaline phosphatase-anti-alkaline phosphatase (APAAP) monoclonal antibody conjugate, and naphthol AS-phosphate/fast red substrate. Chlamydial inclusions stained red and were easily detected against a background of blue hematoxylin-stained nuclei. After 18 h, inclusions of C. trachomatis serovar L2 LGV434/Bu and C. psittaci strain 6BC were stained by APAAP but not by iodine or Giemsa. At 48 h inclusion counts were significantly higher in the APAAP cultures. Both the APAAP procedure and conventional staining detected 35 of 239 (15%) cultures 48 h after inoculation with urethral or endocervical specimens. However, at 24 h after inoculation 22 of 35 (63%) were positive by APAAP staining while negative by iodine. This immunostain also allowed identification of chlamydial inclusions in endometrial biopsies from patients with tubal factor infertility or pelvic inflammatory disease.

Routine screening of gynaecological and obstetric patients for Chlamydia trachomatis

Chlamydia trachomatis infection of the cervix uteri was diagnosed in 9% of 221 gynaecological and obstetric patients. Infection occurred more commonly among obstetric (12.6%) than gynaecological patients (5.5%). In obstetric patients chlamydial infection was commoner in those complaining of excessive vaginal discharge or spontaneous premature rupture of the membranes. Chlamydial infection in gynaecological patients occurred in those with previous pelvic infection, menstrual disorders or excessive vaginal discharge. No cases of chlamydial infection were detected among intrauterine device users. The enzyme immunoassay we used is an easy and relatively quick method of diagnosis for genital chlamydial infection.

Evaluation of enzyme immunoassay (Chlamydiazyme) for detecting Chlamydia trachomatis in genital tract specimens

An enzyme immunoassay (Chlamydiazyme) for detecting Chlamydia trachomatis was evaluated on genital specimens from 96 men and 272 women attending a clinic for sexually transmitted diseases (STD clinic). Compared with a direct immunofluorescence test for chlamydial elementary bodies, the enzyme immunoassay had a sensitivity of 58% on specimens from men, a specificity of 90%, a positive predictive value of 93%, and a negative predictive value of 88%; the assay had a sensitivity of 67% on specimens from women, a specificity of 89%, a positive predictive value of 63% and a negative predictive value of 90%. Immunofluorescence provided the most stringent test for the performance of the enzyme immunoassay as values were improved a little when a cell culture procedure was used for comparison. Further evidence for the lack of sensitivity was the detection of elementary bodies, sometimes in large numbers, in the enzyme immunoassay buffer of 13 of 19 specimens that had given a negative enzyme immunoassay result and the finding in comparative titrations of four laboratory strains that the enzyme immunoassay was at least 100-fold less able to detect chlamydiae than either immunofluorescence or the cell culture procedure. Lack of specificity may be associated with the finding that the enzyme immunoassay antibody reacted with strains of Acinetobacter calcoaceticus, Escherichia coli, Gardnerella vaginalis, Neisseria gonorrhoeae and group B streptococci. The enzyme immunoassay was not considered to be sufficiently sensitive, specific, or reproducible for routine use.

Rapid detection of Chlamydia trachomatis by an enzyme immunoassay method

Chlamydia trachomatis has been shown to be a major cause of sexually transmitted diseases in the United States. An enzyme immunoassay (Abbot Laboratories) has been developed that detects chlamydial antigen directly in the urogenital specimens of patients. We have evaluated specimens from 1,074 patients belonging to one of three risk groups. Three swabs were collected from each patient--one each for Neisseria gonorrhoeae, chlamydia cell culture, and enzyme immunoassay. When compared with cell culture, the sensitivity and specificity of the enzyme immunoassay for symptomatic males and females attending a sexually transmitted disease clinic was 82% and 100%, and 91.3% and 95.0%, respectively. A moderate risk group, consisting of female patients seen at either urology or gynecology clinics for genitourinary symptoms was also evaluated. The sensitivity and specificity of the test on this group was 96% and 96.7%. A population of females at low risk were also screened for chlamydial infection. In this group, the sensitivity and specificity of the enzyme immunoassay was 89.3% and 93.2%, respectively. This rapid test is a highly specific and sensitive procedure for the detection of chlamydial antigen in genital specimens from high risk female patients as well as symptomatic males.

Diagnosis of Neisseria gonorrhoeae and Chlamydia trachomatis infections using antigen detection methods

Rapid antigen detection methods have great potential value in managing sexually transmitted gonococcal and chlamydial infections. Ideally, such tests should be rapid, technically simple, inexpensive, accurate, and applicable to all sites of infection commonly sampled (cervix, urethra, pharynx). For gonorrhea, the Gram stain fulfills these criteria in men with symptomatic urethritis, but lacks sensitivity when used at other sites or in asymptomatic patients. Antigen detection for gonorrhea would thus be of greatest value in 1) the diagnosis of gonococcal cervical infections in women with mucopurulent cervicitis or pelvic inflammatory disease, 2) the diagnosis of gonococcal proctitis in homosexual men, and 3) in situations requiring lengthy specimen transport. Because culture confirmation of Chlamydia trachomatis infections is not widely available, antigen detection tests could be of great value in management of these infections. Major uses include 1) confirming infection in women with cervicitis, endometritis, and pelvic inflammatory disease; 2) screening for asymptomatic infections in high risk groups of women; and 3) confirmation of Chlamydia trachomatis infections in infants and in adult males. The currently available methods for diagnosis of gonococcal and chlamydial infection by antigen detection are reviewed herein. Continued experience with antigen detection tests in well defined populations having high and low risk of gonococcal and chlamydial infection is needed to more fully determine how best to utilize these assays.