Abstract
BackgroundMolecular typing of syphilis-causing strains provides important epidemiologic data. We tested whether identified molecular subtypes were identical in PCR-positive parallel samples taken from the same patient at a same time. We also tested whether subtype prevalence differs in skin and blood samples.ResultsEighteen syphilis positive patients (showing both positive serology and PCR), with two PCR-typeable parallel samples taken at the same time, were tested with both CDC (Centers for Disease Control and Prevention) and sequence-based typing. Samples taken from 9 of 18 patients were completely typed for TP0136, TP0548, 23S rDNA, arp, and tpr loci. The CDC typing revealed 11 distinct genotypes while the sequence-based typing identified 6 genotypes. When results from molecular typing of TP0136, TP0548, and 23S rDNA were analyzed in samples taken from the same patient, no discrepancies in the identified genotypes were found; however, there were discrepancies in 11 of 18 patients (61.1%) samples relative to the arp and tpr loci. In addition to the above described typing, 127 PCR-positive swabs and whole blood samples were tested for individual genotype frequencies. The repetition number for the arp gene was lower in whole blood (WB) samples compared to swab samples. Similarly, the most common tpr RFLP type “d” was found to have lower occurrence rates in WB samples while type “e” had an increased occurrence in these samples.ConclusionsDifferences in the CDC subtypes identified in parallel samples indicated genetic instability of the arp and tpr loci and suggested limited applicability of the CDC typing system in epidemiological studies. Differences in treponemal genotypes detected in whole blood and swab samples suggested important differences between both compartments and/or differences in adherence of treponeme variants to human cells.
Highlights
Molecular typing of syphilis-causing strains provides important epidemiologic data
PCR detection and molecular typing of syphilis treponemes A total of 18 patients had two PCR-typeable samples, which were used for amplification of treponemal TP0136, TP0548, 23S rRNA genes, tpr and arp loci
Samples taken from 9 of 18 patients were completely typed at all loci (TP0136, TP0548, 23S rDNA, arp, and tpr)
Summary
Molecular typing of syphilis-causing strains provides important epidemiologic data. We tested whether identified molecular subtypes were identical in PCR-positive parallel samples taken from the same patient at a same time. Pallidum (T. pallidum), is a sexually transmitted multistage disease with a diagnosis based on clinical symptoms, serological findings and other methods such as direct detection of treponemes by microscopy. In the 1990s, PCR-based methods for direct detection of treponemal DNA were developed [1]. Several improvements in these fragment length polymorphism (RFLP) analysis of the 3 PCR-amplified tpr genes (tprE, G, J). A sequencing-based molecular typing scheme based on sequencing of the TP0136, TP0548 and 23S rRNA genes was introduced [17]. The sequence variants of TP0136, TP0548 and 23S rRNA genes have been shown to independently combine with variants of the arp and tpr genes [17]
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