Outer membrane nanovesicles of gram-negative bacteria Aeromonas hydrophila and Aeromonas salmonicida

Aeromonas hydrophila and A. salmonicida grown in pure cultures were found to secrete extracellular membrane nanovesicles into the environment. Outer membrane nanovesicle preparations were isolated by differential centrifugation and ultrafiltration and visualized by transmission electron microscopy applying the negative staining technique. Membrane nanovesicle size (10-300 nm) and ultrastructure were determined. The vesicles were especially numerous around bacteria at the edge of small colonies. The process of the vesicle budding off the bacterial cell was observed. On ultrathin sections of rat intestine, outer membrane nanovesicles were revealed among bacterial aggregates of various species of parietal microorganisms. Short chains of such vesicles were also detected inside the glycocalyx between the microvilli of the apical surface of the intestine epitheliocytes. On the basis of the results, together with the literature data, the secretion of the outer membrane nanovesicles by pathogenic gram-negative bacteria, such as A. hydrophila and A. salmonicida, is proposed as a possible mechanism of pathogenesis leading to the host disease, as well as a means for cellular interactions both within the prokaryote population and between the bacteria and the host organism.