# Factors Affecting longterm in vitro culture of Treponema pallidum

> **NIH NIH R01** · UNIVERSITY OF TEXAS HLTH SCI CTR HOUSTON · 2020 · $461,283

## Abstract

ABSTRACT
Treponema pallidum and closely related bacteria are the causative agents of syphilis, yaws, bejel (endemic
syphilis), and pinta. Syphilis alone has an estimated prevalence of 18 million cases worldwide, and in 2016 the
total number of reported syphilis cases in the United States was the highest recorded since 1993. One of the
barriers to research on T. pallidum has been the inability to culture the spirochete continuously in vitro; it is one
of the few major bacterial pathogens (along with Mycobacterium leprae) with this distinction. In the preliminary
data for this project, we report the consistent, long-term multiplication of T. pallidum subsp. pallidum, the
causative agent of syphilis, in a tissue culture system. The culture system consists of co-incubation of T. pallidum
with rabbit epithelial cells in a modified tissue culture medium under a microaerobic atmosphere containing 1.5%
O2 and 5% CO2. Exponential multiplication of T. pallidum has been obtained for over 100 days in ongoing
experiments, with excellent retention of viability (as measured by motility) and infectivity (examined by
experimental infection of rabbits). Optimal replication of T. pallidum occurs with subculture at 6 to 7 day intervals
and periodic medium exchange, which are thought to maintain near-homeostatic conditions and to minimize
entrance of the cultures into the stationary phase of growth. In this project we propose to continue and expand
studies on the factors affecting T. pallidum multiplication in this system and to explore its utility in T. pallidum
research, as exemplified by mutational analysis. The specific aims are to 1) determine the optimal conditions
for continuous growth of T. pallidum subspecies and strains in the tissue culture system; 2) utilize the tissue
culture system to define the nutritional requirements with the purpose of achieving culture of T. pallidum under
axenic conditions (i.e. without mammalian cells); and 3) examine the feasibility of genetic analysis of in vitro
cultured T. pallidum through chemical mutagenesis, transformation with oligonucleotides, shuttle vectors and
suicide plasmids, and transposon mutagenesis. The further confirmation and development of the T. pallidum in
vitro culture system will likely facilitate many aspects of T. pallidum research, including studies of physiology,
structure, antimicrobial susceptibility, pathogenesis, and host immunity.

## Key facts

- **NIH application ID:** 10000844
- **Project number:** 5R01AI141958-03
- **Recipient organization:** UNIVERSITY OF TEXAS HLTH SCI CTR HOUSTON
- **Principal Investigator:** Diane G Edmondson
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $461,283
- **Award type:** 5
- **Project period:** 2018-09-17 → 2023-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10000844

## Citation

> US National Institutes of Health, RePORTER application 10000844, Factors Affecting longterm in vitro culture of Treponema pallidum (5R01AI141958-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10000844. Licensed CC0.

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