Bacterial acquisition of antimicrobial resistance (AMR) genes via horizontal gene transfer (HGT) has contributed to the rise of antibiotic resistance globally. Recently, outer membrane vesicles (OMVs), released by all Gram-negative bacteria, have been described as a novel mechanism of HGT. OMVs package and protect DNA and can transfer DNA to recipient bacteria, however this has only been observed for a limited number of bacterial species. In this study, we aimed to examine OMVs produced by the opportunistic pathogen Pseudomonas aeruginosa to determine their ability to package, protect, and transfer DNA, and whether bacterial growth conditions, such as planktonic or biofilm growth conditions altered DNA packaging within P. aeruginosa OMVs.
To do this, P. aeruginosa OMVs were isolated from planktonic cultures and were found to package and protect DNA, including plasmid DNA encoding for an AMR gene. DNase treatment of planktonic derived OMVs revealed that a small proportion of DNA was contained within OMVs which was protected from DNase degradation. Planktonic derived P. aeruginosa OMVs were able to transfer plasmid DNA encoding for an AMR gene to recipient P. aeruginosa at a greater efficiency than transformation with plasmid DNA alone. In comparison, OMVs isolated from biofilm cultures of P. aeruginosa contained more copies of plasmid DNA that was protected from DNase treatment, compared to planktonic derived OMVs. Furthermore, P. aeruginosa biofilm derived OMVs were more efficient at transferring plasmid DNA to recipient P. aeruginosa compared to planktonic derived P. aeruginosa OMVs. We are currently testing the transformation efficiency of biofilm derived P. aeruginosa OMVs when added to recipient P. aeruginosa biofilms, to determine the natural occurrence of OMV-mediated HGT.
Collectively, these studies will advance our limited knowledge regarding DNA packaged within OMVs and the contribution of OMVs to the transfer of AMR genes to facilitate the spread of antibiotic resistance.