Molecular Detection of Chlamydia trachomatis and Neisseria gonorrhoeae is Enhanced by Flocked Swabs and Universal Transport Media
Background: Nucleic acid amplification tests (NAATs) are used to diagnose Chlamydia trachomatis and Neisseria gonorrhoeae. A universal transport system would enable confirmatory testing. The objective was to compare a room temperature universal transport media (UTM-RT) and flocked swabs (FS, Copan, Diagnostics Inc.) to swabs and transport systems of commercial NAATs in mocked specimens.
Methods: Laboratory strains of CT and GC were diluted in UTM-RT from 10-1 to 10-10 and aliquoted into tubes for each dilution using FS, ProbeTec swabs (PT, Becton Dickinson), Amplicor swabs (AMP, Roche Diagnostics), and APTIMA Combo 2 swabs (AC2, Gen-Probe Inc.). Each was processed into kit-dilution buffers as a mocked sample. Dilutions of CT in UTM-RT were inoculated into McCoy cells and scored for fluorescent inclusions. GC dilutions in UTM-RT were compared to dilutions in TSB 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 system enhanced the ability of commercial NAATs to detect low levels of CT or GC. The use of this universal system might yield more positives from clinical specimens and enable confirmatory testing from one assay to another.