Practical Pearls for Direct Detection of Live Treponema pallidum in Primary Syphilis Using a Phase-Contrast...

Syphilis cases are increasing in Japan, highlighting the urgent need for rapid and accurate diagnosis. In primary syphilis, serological tests may yield negative results, so direct microscopic observation of Treponema pallidum remains an important but often underused diagnostic method. We present a simple, widely accessible phase-contrast microscopy system, featuring a USB camera and monitor, enabling high-clarity, real-time observation of live wild-type treponemes directly from patient lesions. Specimens obtained from firm chancre rubs, mounted on sealed slides, were examined under oil immersion using 40× or 100× objective lenses. Treponemes were detectable within minutes, and serial imaging revealed striking morphological changes over time. Compared to dark-field microscopy, phase contrast provided superior image sharpness, digital recording capability, and greater value for patient education. Our video atlas is among the few contemporary records of motile wild-type T. pallidum, linking historical morphological studies to modern clinical practice. This inexpensive and reproducible method is well-suited for revitalizing microscopic diagnosis, training, and morphological research in syphilis.