The Salmonella Typhi SPI-2 injectisome enigma

Area of Science:

• Microbiology
• Immunology
• Bacterial Pathogenesis

Background:

• The Salmonella pathogenicity island 2 (SPI-2) type III secretion system (injectisome) is essential for Salmonella Typhimurium intracellular growth.
• Its role in Salmonella Typhi is less clear, with inconsistent results in human macrophages.
• Understanding the S. Typhi SPI-2 injectisome is vital for developing live attenuated S. Typhi vaccines.

Purpose of the Study:

• To clarify the functions of the S. Typhi SPI-2 injectisome in human macrophages.
• To investigate potential reasons for conflicting results regarding S. Typhi SPI-2 injectisome activity.
• To compare the injectisome's function between S. Typhi and S. Typhimurium in relevant host models.

Main Methods:

• Comparative analysis of Salmonella Typhimurium and Salmonella Typhi injectisome gene expression and effector delivery in human macrophages.
• Investigation of core effector gene presence and potential function in both Salmonella species.
• Utilizing mammalian cell culture models to study intracellular bacterial behavior.

Main Results:

• Intracellular expression of injectisome genes and effector delivery are delayed in the S. Typhi/human macrophage model compared to S. Typhimurium.
• Both S. Typhimurium and S. Typhi possess intact genes for core effectors involved in vacuole membrane regulation.
• These core effectors contribute to intracellular bacterial replication in S. Typhimurium.

Conclusions:

• The observed differences in S. Typhi SPI-2 injectisome function in human macrophages may be attributed to delayed gene expression and effector translocation.
• Core effectors likely play similar roles in vacuole membrane regulation and intracellular replication for both S. Typhi and S. Typhimurium.
• Further research into the S. Typhi SPI-2 injectisome is warranted, particularly concerning its implications for vaccine development.