E-Poster with pre-recorded video presentation Lorne Infection and Immunity 2021

Antimicrobial activity of outer membrane vesicles against Gram‑negative and Gram‑positive bacteria is altered by their mechanism of biogenesis (#226)

Lauren Zavan 1 2 , Maria Liaskos 1 2 , Cynthia Whitchurch 3
  1. Department of Physiology, Anatomy and Microbiology, La Trobe University, Bundoora, Victoria, Australia
  2. Research Centre for Extracellular Vesicles, La Trobe University, Bundoora, Victoria, Australia
  3. Quadram Institute Bioscience, Norwich Research Park, NR4 7UQ, Norwich, UK

Outer membrane vesicles (OMVs) are nanoparticles naturally produced by all Gram‑negative bacteria. OMVs are produced by budding from the cell membrane during bacterial growth or by prophage‑induced explosive cell lysis resulting in bacterial membrane fragments ligating to form OMVs. Depending on their cargo composition, OMVs have numerous roles including the lysis of competing bacterial species as an antimicrobial defence mechanism. Although bacteria can regulate the cargo composition and functions of OMVs throughout bacterial growth, it is unknown whether the mechanism of OMV biogenesis can also affect their composition and functions. Therefore, in this study we examined whether different mechanisms of OMV biogenesis can regulate OMV cargo composition and their subsequent antimicrobial functions.

We isolated OMVs from three Pseudomonas aeruginosa strains; PAO1 which releases OMVs naturally by budding, PAO1Δlys which cannot undergo explosive cell lysis, and PAO1Δlys pJN105lys which produces OMVs via the inducible expression of explosive cell lysis. The antimicrobial activity of these OMVs was tested against P. aeruginosa and Staphylococcus aureus. OMVs generated naturally from PAO1 and PAO1Δlys were unable to inhibit the growth of P. aeruginosa. However, OMVs produced via explosive cell lysis could inhibit P. aeruginosa growth. Interestingly, OMVs isolated from all P. aeruginosa strains were able to significantly inhibit the growth of S. aureus. These results suggest there are differences in the antimicrobial functions of OMVs against Gram‑negative and Gram‑positive bacteria.

Collectively, our data shows that P. aeruginosa OMVs generated by explosive cell lysis can inhibit both P. aeruginosa and S. aureus growth whilst OMVs generated via budding from the cell membrane can only inhibit S. aureus growth and not that of their parent bacterium. These findings provide insight into the regulation of OMV cargo composition and will enable us to advance our understanding of how OMV biogenesis dictates OMV content and their subsequent antimicrobial functions.