Outer membrane vesicles isolated from two clinical Acinetobacter baumannii strains exhibit different toxicity and proteome characteristics

• The clinical MDRAb strain A38 produced more OMVs compared with the non-MDRAb strain 5806.
• A38 OMVs induced more powerful cytotoxicity and stronger innate immune responses compared with 5806 OMVs.
• LC-MS/MS analysis showed more virulence factors enriched in A38 OMVs.
• Further studies are needed to confirm whether this phenomenon is observed for all MDR and non-MDR strains.

Outer membrane vesicles (OMVs) are well-characterized virulence factors produced by Gram-negative bacteria. Here, we isolated two clinical Acinetobacter baumannii strains, the multidrug-resistant A. baumannii (MDRAb) A38 and non-MDRAb 5806. Strain A38 produced more abundant OMVs than strain 5806 when cultured to the early stationary phase. The results from cell proliferation assays and real-time PCR analyses indicated that A38 OMVs induced more powerful cytotoxicity and stronger innate immune responses compared with 5806 OMVs. Moreover, SDS-PAGE and LC-MS/MS analyses revealed that A38 OMVs contained more virulence factors, including Omp38, EpsA, Ptk, GroEL, hemagglutinin-like protein, and FilF. Taken together, the results of the present study suggest that MDRAb might produce abundant OMVs with more virulent factors facilitating the worse outcome, a finding that merits further study.