A universal transport Medium and Flocked swabs enhanced the detection of chlamydia trachomatis and neisseria gonorrhoeae in nucleic Acid Amplification Assays

ABSTRACT

Background: Chlamydia trachomatis [CT] and Neisseria gonorrhoeae [GC] infections are common and nucleic acid amplification tests [NAAT] are used extensively for their diagnosis. The objective was to compare a room temperature universal transport media [UTM-RT] and flocked swabs [FS] (Copan, Diagnostics Inc.) to the swabs and transport systems of Gen-Probe Aptima Combo 2 [AC2] Amplicor [AMP] swabs [Roche] and Becton Dickinson ProbeTec ET [PT] for the detection of CT and GC in mocked specimens.

Methods: Laboratory strains of CT and GC were serially diluted ten fold in UTM-RT from 10-1 to 10-10 and 0.3 ml of each dilution was aliquoted into tubes for each dilution using FS, and commercial swabs. Each swab was processed into appropriate kit-dilution buffers as a mocked sample. Dilutions of CT in UTM-RT were also inoculated into shell vials containing McCoy cells and scored after 48 hours for fluorescent inclusions. GC dilutions in UTM-RT were compared to dilutions in TSB [both with FS] with colony counts.

Results: For CT the 100% endpoints for FS and kit swabs [KS] were equal in AC2 [10-7] and PT [10-6]. In AMP the FS 100% endpoint was 10-7 compared to 10-6 for the Roche swab. Small numbers of replicates were positive to higher dilutions for all swab types [for AC2 the FS yielded 50% and the KS 10% positive between 10-8 and 10-10. The CT culture endpoint was 10-6. For GC the 100% endpoints for FS and KS were equal for AC2 [10-6], PT and AMP [10-5]; but at 10-7 90% of FS and 70% of KS were positive in AC2 and higher proportions of replicates were positive with FS at 10-6 in the other 2 assays. GC infectivity titrated to 10-6.

Conclusions: The UTM/FS combination from Copan enhanced the ability of each NAAT to detect samples containing low levels of CT or GC. The use of this system might yield more positives from clinical specimens and enable confirmatory testing of low level positives from one assay to another.

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