Acetate metabolic requirement of avian pathogenic Escherichia coli promotes its intracellular proliferation within macrophage

Area of Science:

• Microbiology
• Pathogenesis
• Bacterial Metabolism

Background:

• Avian pathogenic Escherichia coli (APEC) is a significant cause of disease in poultry.
• Intracellular survival within macrophages is critical for APEC's ability to spread within the host.
• The metabolic strategies employed by APEC for intracellular proliferation remain incompletely understood.

Purpose of the Study:

• To investigate the role of the acetate assimilation system in APEC's intracellular replication and virulence.
• To elucidate the contribution of acetate metabolism to APEC pathogenesis within macrophages.
• To identify novel intracellular survival factors in APEC.

Main Methods:

• Identification and characterization of the APEC acs-yjcH-actP operon involved in acetate assimilation.
• Analysis of host-induced transcription of the acetate assimilation system during macrophage infection.
• Construction and phenotypic analysis of APEC mutant strains lacking the acetate assimilation system (e.g., FY26∆acs-yjcH-actP).
• Quantitative reverse transcription PCR (qRT-PCR) to assess cytokine and iNOS expression in infected macrophages.
• In vivo virulence and colonization assays in avian colibacillosis models.

Main Results:

• The APEC acetate assimilation system (acs-yjcH-actP operon) is upregulated during intracellular replication in macrophages.
• Deletion of the acetate assimilation system significantly reduced APEC replication within macrophages.
• APEC mutants lacking the acetate assimilation system exhibited decreased cytotoxicity towards macrophages.
• Pro-inflammatory cytokine and iNOS production was significantly downregulated in macrophages infected with the mutant strain.
• In vivo studies demonstrated attenuated virulence and colonization in avian lungs for the mutant strain, indicating the system's role in early colonization.

Conclusions:

• The acetate assimilation system is a novel intracellular survival factor promoting APEC replication and virulence within macrophages.
• Intracellular acetate consumption by APEC contributes to immunomodulatory disorders and excessive pro-inflammatory responses.
• Targeting this metabolic pathway could offer new strategies for controlling APEC infections in poultry.