Acinetobacter baumannii Clinical Isolates Resist Complement-Mediated Lysis by Inhibiting the Complement Cascade and...

Area of Science:

• Immunology
• Microbiology
• Genetics

Background:

• Acinetobacter baumannii is a dangerous opportunistic pathogen.
• The human complement system, including the membrane attack complex (MAC), defends against bacterial infections.
• A. baumannii employs evasion strategies against complement-mediated lysis.

Purpose of the Study:

• To investigate the mechanisms by which A. baumannii evades complement.
• To determine the role of capsule type in complement resistance and virulence.

Main Methods:

• Flow cytometry and Western blotting for complement deposition.
• ELISA for soluble MAC formation.
• SYTOX Green Assay for serum resistance.
• Galleria mellonella infection model.
• Whole genome sequencing.

Main Results:

• 11 of 16 clinical isolates showed MAC deposition; 5 did not.
• MAC-negative isolates exhibited increased serum resistance and virulence.
• MAC-negative isolates inhibited alternative pathway activation.
• Genome sequencing revealed more virulence genes in MAC-negative strains.
• Distinct capsule types were associated with MAC deposition or inhibition (e.g., KL171 vs. KL230).

Conclusions:

• Capsule type is linked to complement resistance in A. baumannii.
• A. baumannii capsule type influences virulence and evasion of innate immunity.
• Findings highlight the interplay between bacterial genetics, immune evasion, and pathogenesis.