Outer Membrane Vesicles Formed by Clinical Proteus mirabilis Strains May Be Incorporated into the Outer Membrane of Other P. mirabilis Cells and Demonstrate Lytic Properties

Outer membrane vesicles (OMVs) are extracellular structures, ranging in size from 10 to 300 nm, produced by Gram-negative bacteria. They can be incorporated into the outer membrane of a recipient's cells, which may enable the transfer of substances with lytic properties. Due to the scarce information regarding the OMVs produced by <i>Proteus mirabilis</i>, the aim of this study was to test the blebbing abilities of the clinical <i>P. mirabilis</i> O77 and O78 strains and to determine the blebs' interactions with bacterial cells, including their possible bactericidal activities. The production of OMVs was visualised by Transmission electron microscopy (TEM). The presence of OMVs in the obtained samples as well as the phenomenon of OMV fusion to recipient cells were confirmed by Enzyme-Linked ImmunoSorbent Assay (ELISA) and Western blotting assays. The bacteriolytic activity of the OMVs was examined against <i>P. mirabilis</i> clinical strains and reference <i>Staphylococcus aureus</i> and <i>Escherichia coli</i> strains. It was shown that each of the two tested <i>P. mirabilis</i> strains could produce OMVs which were able to fuse into the cells of the other strain. The lytic properties of the O78 OMVs against another <i>P. mirabilis</i> O78 strain were also demonstrated. This promising result may help in the future to better understand the mechanisms of the pathogenesis and to treat the infections caused by <i>P. mirabilis</i>.