Salmonella enterica serovar Typhi (S. Typhi) and the related serovar S. Paratyphi cause typhoid fever in humans, a devastating disease that results in ~200,000 deaths every year. Although most of the cases occur in developing countries, outbreaks occasionally occur in the United States. Unlike other Salmonella enterica serovars, which can infect a variety of hosts and can cause limited gastroenteritis, S. Typhi is an exclusive human pathogen and causes systemic, often lethal, disease. Despite its Public Health importance, the mechanisms of pathogenesis of typhoidal Salmonellae remain poorly understood. Our laboratory has been exploring the unique aspects of S. Typhi pathogenesis and devoted a substantial amount of effort to the study of typhoid toxin, an A2B5 toxin that is highly conserved in typhoidal Salmonella serovars (i. e. S. Typhi and S. Paratyphi), but that it is largely absent from non-typhoidal Salmonellae. Typhoid toxin is an atypical AB toxin in that, unlike all known AB5 toxin family members, it has two enzymatically active subunits: an ADP ribosyl transferase (PltA) with an as of yet unidentified host target, and a deoxyribonuclease (CdtB), which inflicts DNA damage on intoxicated cells. These two subunits are covalently linked to one another and are associated to a homopentameric B subunit composed of PltB. Typhoid toxin is uniquely adapted to humans as it recognizes Neu5Ac-terminated sialoglycans on surface glycoproteins. Administration of typhoid toxin to experimental animals can reproduce many of the acute pathognomonic symptoms of typhoid fever, including stupor and lethargy, which most likely involve the central nervous system (CNS). Typhoid toxin exhibits a remarkable biology in that it is only produced by intracellular bacteria, and after its synthesis and assembly, it is released into the Salmonella-containing vacuole and subsequently transported to the extracellular space by specific vesicle transport carriers. During the past funding period we have unraveled many mechanistic aspects of the biology of typhoid toxin, including the description of its unique mechanism of intracellular expression, the characterization of all the steps of its remarkable transport pathways, the discovery of novel bacterial protein secretion mechanism, the description of its unique evolutionary history, and the discovery of an alternative form of typhoid toxin. Finally, these studies have led to the discovery of a novel cell-intrinsic pathogen restriction mechanism that prevents the replication of S. Typhi in mouse tissues and that it is antagonized by the mouse pathogen S. Typhimurium through the activity of specific type III protein secretion effectors absent from S. Typhi. These studies have raised very important questions related to pathogenesis of typhoid fever that we intend to pursue during the next funding period.

Public Health Relevance

Salmonella enterica serovar Typhi (S. Typhi), the cause of typhoid fever in humans, continues to be a very significant health problem. Unlike other Salmonella enterica serovars, which can infect a variety of hosts and can cause food poisoning, S. Typhi is an exclusive human pathogen where it causes typhoid fever, a life- threatening disease. It is estimated that there are ~20,000,000 cases of typhoid fever every year, resulting in ~200,000 deaths. Although most of the cases occur in developing countries, outbreaks occasionally occur in the United States. There are no effective vaccines to protect against these infections. The studies proposed in this Grant application may serve as the foundation for novel therapeutic and prevention strategies against typhoid fever.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
2R01AI114618-06
Application #
9879404
Study Section
Bacterial Pathogenesis Study Section (BACP)
Program Officer
Alexander, William A
Project Start
2014-09-16
Project End
2024-08-31
Budget Start
2019-09-23
Budget End
2020-08-31
Support Year
6
Fiscal Year
2019
Total Cost
Indirect Cost
Name
Yale University
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
043207562
City
New Haven
State
CT
Country
United States
Zip Code
06520
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Fowler, Casey C; Galán, Jorge E (2018) Decoding a Salmonella Typhi Regulatory Network that Controls Typhoid Toxin Expression within Human Cells. Cell Host Microbe 23:65-76.e6
Spanò, Stefania; Galán, Jorge E (2018) Taking control: Hijacking of Rab GTPases by intracellular bacterial pathogens. Small GTPases 9:182-191
Fowler, Casey C; Chang, Shu-Jung; Gao, Xiang et al. (2017) Emerging insights into the biology of typhoid toxin. Curr Opin Microbiol 35:70-77
Hannemann, Sebastian; Galán, Jorge E (2017) Salmonella enterica serovar-specific transcriptional reprogramming of infected cells. PLoS Pathog 13:e1006532
Gao, Xiang; Deng, Lingquan; Stack, Gabrielle et al. (2017) Evolution of host adaptation in the Salmonella typhoid toxin. Nat Microbiol 2:1592-1599
Chang, Shu-Jung; Song, Jeongmin; Galán, Jorge E (2016) Receptor-Mediated Sorting of Typhoid Toxin during Its Export from Salmonella Typhi-Infected Cells. Cell Host Microbe 20:682-689
Galán, Jorge E (2016) Typhoid toxin provides a window into typhoid fever and the biology of Salmonella Typhi. Proc Natl Acad Sci U S A 113:6338-44
Spanò, Stefania; Gao, Xiang; Hannemann, Sebastian et al. (2016) A Bacterial Pathogen Targets a Host Rab-Family GTPase Defense Pathway with a GAP. Cell Host Microbe 19:216-26
Song, Jeongmin; Wilhelm, Cara L; Wangdi, Tamding et al. (2016) Absence of TLR11 in Mice Does Not Confer Susceptibility to Salmonella Typhi. Cell 164:827-8

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