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Open Access Research article

Comparison of CDC and sequence-based molecular typing of syphilis treponemes: tpr and arp loci are variable in multiple samples from the same patient

Lenka Mikalová1, Petra Pospíšilová1, Vladana Woznicová2, Ivana Kuklová3, Hana Zákoucká4 and David Šmajs1*

Author Affiliations

1 Department of Biology, Faculty of Medicine, Masaryk University, Brno, Czech Republic

2 Department of Medical Microbiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic

3 Department of Dermatology, 1st Faculty of Medicine, Charles University in Prague, Prague, Czech Republic

4 National Reference Laboratory for Diagnostics of Syphilis, The National Institute for Public Health, Prague, Czech Republic

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BMC Microbiology 2013, 13:178  doi:10.1186/1471-2180-13-178

Published: 30 July 2013

Abstract

Background

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. We also tested whether subtype prevalence differs in skin and blood samples.

Results

Eighteen 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.

Conclusions

Differences 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.

Keywords:
Treponema pallidum; Syphilis; Molecular typing; Sequence-based typing; CDC typing; arp gene; tpr genes