Shigella sonnei Does Not Use Amoebae as Protective Hosts.

Area of Science:

• Microbiology
• Infectious Diseases
• Environmental Health

Background:

• Shigella flexneri and Shigella sonnei cause most shigellosis globally.
• S. sonnei is increasingly prevalent in middle- and high-income countries, unlike S. flexneri.
• Amoebae were proposed as a protective host for S. sonnei's environmental survival and spread.

Purpose of the Study:

• To investigate if Acanthamoebae castellanii serves as a protective host for Shigella sonnei.
• To determine if amoebae contribute to the environmental persistence and range expansion of S. sonnei.

Main Methods:

• Coculturing Shigella sonnei and Shigella flexneri with Acanthamoebae castellanii.
• Observing bacterial survival and growth patterns during coculture.
• Assessing bacterial degradation following phagocytosis by A. castellanii.

Main Results:

• Both S. sonnei and S. flexneri survived coculture with A. castellanii, but growth was primarily extracellular.
• All tested Shigella isolates were degraded after phagocytosis by A. castellanii.
• Unlike Legionella pneumophila, Shigella did not replicate intracellularly within amoebae.

Conclusions:

• Amoebae are unlikely to act as a protective environmental host for Shigella sonnei.
• Alternative explanations are needed to understand the emergence and persistence of S. sonnei infections in diverse socioeconomic settings.
• Findings challenge the hypothesis that amoebic protection drives S. sonnei's expanding range.