Cross-reaction of clinical isolates of bacteria and yeasts with the chlamydiazyme test for chlamydial antigen, before and after use of a blocking reagent.

More than 1,000 clinical isolates of bacteria and yeasts were identified, subcultured, and tested at 10(8) colony-forming units per milliliter with the Chlamydiazyme assay to determine the variety of microorganisms which could cause false-positive results for Chlamydial antigen. False-positive Chlamydiazyme results were obtained from 27 of 465 (5.8%) gram-negative, aerobic, or facultatively anaerobic bacterial isolates (including 8 of 39 [20.5%] Neisseria gonorrhoeae and 8 of 149 [5.4%] Escherichia coli isolates) and also from 2 of 46 (4.3%) Bacteroides species isolates. No false-positive results were obtained either from 373 gram-positive bacterial isolates or from 153 yeasts. Results from 21 of 29 (72.4%) isolates that cross-reacted with Chlamydiazyme antibodies were repeatedly positive, but all 21 were confirmed as false-positive results using a blocking antibody. When an initial Chlamydiazyme result is positive, repeating the test, with and without use of the blocking antibody, appears to be effective in identifying those results (more likely from poorly collected endocervical specimens) that are falsely positive, even in the presence of high concentrations of cross-reacting bacteria. Microscopic determination of endocervical specimen adequacy also may help to minimize false-positive (and false-negative) Chlamydiazyme results.