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.