Molecular subtyping of Treponema pallidum from North and South Carolina.

Patients from five clinics in North and South Carolina who had lesions suggestive of primary or secondary syphilis were evaluated using molecular techniques that allow the differentiation of Treponema pallidum strains on the basis of two variable genes, tpr and arp. Lesion samples were screened for the presence of T. pallidum DNA using PCR for polA, which represents a segment of the polymerase I gene that is unique to the spirochete. Twenty-seven of 154 lesion samples were found to contain T. pallidum, 23 of which had typeable DNA. Seven molecular subtypes were found (10f, 12f, 13f, 14f, 14g, 15f, and 16f); one to four subtypes were identified at each clinic. Subtype 14f was found in 52% of the typeable specimens and was distributed in four of the five clinics. Subtype 16f was found in 22% of specimens and was concentrated at one clinic. Further data are needed to define the role of this technique in examining the epidemiology of syphilis.

Defibrination of blood plasma for use in serological tests for syphilis.

Syphilitic plasma can be salvaged from discarded blood donations and converted to serum by defibrination. Sixty-nine units of plasma were treated with a stock solution of 100 U of thrombin per ml in 1 M calcium chloride and then with a 10% (wt/vol) solution of kaolin. Fibrinogen concentrations detected in initial plasma samples ranged from 94 to 4970 mg/liter (mean, 2532 mg/liter) for samples that were reactive by the rapid plasma reagin circle card test (RPR) and from 314 to 2742 mg/liter (mean 1528 mg/liter) for samples that were not reactive by the RPR. The treated samples showed no measurable fibrinogen remaining after the defibrination process. In the nontreponemal RPR for syphilis, 86% of the treated plasma samples retained the same endpoint titer as that of the initial plasma sample. When the Treponema pallidum passive-particle-agglutination test was used, 98% retained the same reactivity. In the Captia Syphilis-G enzyme immunoassay, 89% of the treated samples demonstrated no change in reactivity index, and in the fluorescent treponemal antibody absorption test, 96% showed no reduction in fluorescence. Human sera containing antibodies to syphilis are used at the Centers for Disease Control and Prevention for the preparation of reference controls or as samples for proficiency testing. Finding reactive sera is becoming more difficult due to the general decline of syphilis cases in the United States. The decreasing availability of these sera can be alleviated by salvaging plasma and converting it to serum.