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The purpose of this study was to investigate the properties of several antimicrobial agents found to be effective against Chlamydia trachomatis and to verify the eradication therapy schedule. The in vitro activities of two quinolones (sparfloxacin, ofloxacin), of three macrolides (azithromycin, erythromycin, clarithromycin) and of a tetracycline (doxycycline) against C. trachomatis were evaluated by several methods for the determination of the minimum inhibitory concentration (MIC) and minimal lethal concentration (MLC). MLC of azithromycin was only 2 times higher than that of MIC. On the other hand, MLCs of other antibiotics were 4–16 times higher than their respective MICs. When all antimicrobial agents were added to the infected culture at different times, we found that the quinolones even at a concentration of 64 μg/ml could not inhibit the formation of inclusion if they were added after 20 h from the start of infection. The corresponding period for macrolides and doxycycline was 24 h. When the antibiotics were removed at 8 h after the start of the infection, all antibiotics except azithromycin and clarithromycin were needed at a concentration much higher than their MLCs to inhibit the formation of inclusion. We consider macrolides, especially azithromycin, to be an excellent anti-C. trachomatis drug because of its lower MICs and MLCs values which were also closer together.

Aims-To examine the detection limit of the ligase chain reaction kit for Chlamydia trachomatis, to study the inhibitory eVect of phosphate on the ligase chain reaction, and to clarify the mechanism of inhibition. Methods-Three reference serovars of C trachomatis-D/UW-3/Cx, F/UW-6/Cx, and L2/434/Bu-were used to test the sensitivity of the chlamydia ligase chain reaction. Comparison was made of the inhibition by phosphate before and after DNA amplification. Phosphate in up to 2.4 mM concentration was added to specimens of C trachomatis serovar D (1 to 50 inclusion forming units (IFU)/reaction) before DNA amplification to examine the concentration dependency of phosphate inhibition of the ligase chain reaction. Results-The detection limits were 0.6 IFU/reaction for serovar D/UW-3/Cx and F/UW-6/Cx, and 0.4 IFU/reaction for L2/ 434/Bu. Phosphate inhibited the ligase chain reaction only when it was added before the amplification stage. The specimens containing chlamydia at 1 to 50 IFU/reaction were negative when the concentration of phosphate added at the prethermocycle stage was more than 1.2 mM. Conclusions-Ligase chain reaction analysis is a reliable method of diagnosing C trachomatis infection because of its high sensitivity. It would be clearly superior to the currently used methods if the problem of inhibitors could be eliminated. The mechanism of inhibition of the ligase chain reaction by phosphate was thought to be blockade of the amplification of the target DNA. The eYcacy of the ligase chain reaction could be inhibited by phosphate in the urine, so duplicate dilution analysis of some negative specimens should be useful. (J Clin Pathol 1998;51:306-308) Keywords: Chlamydia trachomatis; ligase chain reaction; phosphate inhibition Chlamydia trachomatis, an obligate intracellular bacterium, is the major cause of sexually transmitted disease in well developed countries. In men who are sexually active this organism causes about 50% of cases of non-gonococcal urethritis.1 Asymptomatic infection is characteristic of this pathogen. In women, asymptomatic cervicitis contributes to many sequelae. Furthermore, maternal chlamydial infections have a direct and harmful influence on the fetus and can lead to several diseases in infants. Therefore, rapid, accurate, reliable, non-invasive, and convenient tests to detect C trachomatis are required for clinical screening. A genetic detection kit for C trachomatis-plasmid based ligase chain reaction-has been developed (Abbott Laboratories, Chicago, Illinois, USA).2 The specificity of this kit was reported to be better than that achieved by the polymerase chain reaction (PCR) (Amplicor, Roche Diagnostic Systems, Branchburg, New Jersey, USA).Sensitive and specific identification of C trachomatis in clinical specimens is essential for the eVective control of chlamydial infection. However, as the sensitivity increases, so does the possibility of false negative results. One of the reasons for false negatives is the presence of inhibitors in the test sample. In the present s...

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A study was undertaken with different serovars (D, E, F, L2, MoPn) of Chlamydia trachomatis to determine the analytical sensitivity of a new dual amplified immunoassay (IDEIA PCE Chlamydia) for detecting chlamydial lipopolysaccharide. IDEIA PCE Chlamydia incorporates a polymer conjugate consisting of multiple copies of antibody and enzyme molecules to provide signal amplification. The test was also assessed with different protein A producing strains of Staphylococcus aureus in order to assess whether the use of a multiple antibody conjugate increased nonspecific binding. The detection limits varied for each serovar with a detection limit of 38 IFU/ml obtained with serovar F and 237 IFU/ml obtained with serovar D. The incorporation of the polymer conjugate resulted in a 2-5 fold increase in analytical sensitivity compared to an earlier version of the test using a conventional conjugate. No increase in cross reactivity with protein A producing strains of S. aureus was obtained. The new dual amplified test format offers potential as a sensitive low-cost screening assay for C. trachomatis infections.