PRELIMINARY EVALUATION OF THE LIGASE CHAIN-REACTION FOR SPECIFIC DETECTION OF NEISSERIA-GONORRHOEAE

Rapid identification of Neisseria gonorrhoeae in clinical specimens is essential for effective control. Traditional culture requires a minimum of 24 h, and for some specimens harboring gonococci, the gonococci fail to grow or are misidentified. The recently described ligase chain reaction (LCR) is a highly specific and sensitive DNA amplification technique which was evaluated as an alternative to routine culture. Three LCR probe sets were used. Two of the probe sets were directed against the multi-copy Opa genes (Omp-II), while the third set was targeted against the multicopy Pilin genes. Each LCR probe set was evaluated with 260 microorganisms including 136 global isolates of N. gonorrhoeae, 41 isolates of N. meningitidis, and 10 isolates of N. lactamica; 26 nonpathogenic Neisseria strains; and 47 isolates of non-Neisseria species that may reside in clinical specimens. Amplification products were detected by using the IMx LCR format (Abbott Laboratories, Abbott Park, Ill.). Strains of N. gonorrhoeae were assayed at 270 cells per LCR (approximately 6.7 x 10(4) CFU/ml) with the Opa and Pilin probes, producing signals at least 21 and 15 times above background, respectively. In contrast, only background values were observed when testing the probe sets with 124 nongonococcal strains at 1.3 x 10(6) cells per LCR (approximately 3.2 x 10(8) CFU/ml). One hundred urogenital specimens were assayed by LCR, and compared with culture, the three probes were 100% sensitive (8 of 8) and 97.8% specific (90 of 92), resulting in an agreement of 98% (98 of 100). On the basis of the results of these preliminary studies, LCR has the potential to be an accurate and rapid DNA probe assay for the detection of N. gonorrhoeae in clinical specimens.