Background
The difficulty in culturing Treponema pallidum (T. pallidum) has limited molecular-biological analyses. This study aims to establish a molecular epidemiological analysis using the multi-locus sequence typing (MLST) scheme with whole blood specimens and to explore the relationship between T. pallidum bacteremia and its associated pathophysiology.
Methods
We used whole blood specimens from participants serologically diagnosed with syphilis in Tokyo, Japan, between February 2019 and June 2022, about 97% of whom were men who have sex with men (MSM). Sequences for three loci (TP0136, TP0548, and TP0705) required for MLST were obtained, and we analyzed the relationship between PCR positivity and associated markers (e.g., C-reactive protein (CRP), rapid plasma regain (RPR), T. pallidum latex agglutination (TPLA))
Results
Of the 71 whole blood samples, 26 (36.6%) were PCR-positive for TP0136, and sequences for the three loci required for MLST were obtained from 22 samples (31.0%). The most frequently detected sequence type (ST) was ST3 (n=9), followed by ST6 (n=6). Phylogenetic analysis showed that 12 samples belonged to the SS14-like genetic group (12/20, 60%), while 8 samples were classified within the Nichols-like group (8/20, 40%). A new allele was identified in TP0136. Notably, Treponema pallidum subsp. endemicum, the causative agent of bejel, was detected in three samples (12%, 3/26). The Cochran-Armitage test for trend also failed to reveal an increase in TP0136 detection as TPLA levels increased (p = 0.056, Table 3). Similarly, the TP0136 detection rate did not exhibit a significant association with the RPR cut-offs of 10 RU (p = 0.40) or 100 RU (p = 0.21). The trend test did not show an increase in TP0136 detected as the RPR increased (p = 0.12). In contrast, positive CRP levels were significantly associated with TP0136 detection at cut-offs of 0.1 mg/dL (p = 0.0007) or 0.5 mg/dL (p < 0.0001). For CRP ≥ 0.5 mg/dL, 77.0% were positive for TP0136. A trend test further revealed that TP0136 detection significantly increased as CRP levels increased (p < 0.0001)
Conclusions
Both SS14-like and Nichols-like strains were circulating concurrently, and Treponema pallidum subsp. endemicum (TEN) may have been sexually transmitted among Japanese MSM. CRP serves as an indicator of test efficiency and could be linked to the presence of pathogens in the bloodstream.