Pili of Aeromonas hydrophila: Purification, Characterization, and Biological Role

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Abstract
Aeromonas hydrophila (Ae6) has 2 morphologically distinctive kinds of pili. One appeared rigid, channeled, and straight with a diameter of 9 nm (Ae6‐R pili). The other looked flexible, wavy, and having helical structure with a diameter of 7 nm (Ae6‐W pili). Ae6‐R pili were purified and characterized. The pili consisted of a subunit protein with a molecular weight of 18 kDa as estimated by SDS‐PAGE, and contained 42.3% hydrophobic amino acids and one cysteine residue. The pilus was solubilized to 18 kDa subunit protein by 2‐mercaptoethanol, dithiothreitol, hydrochloric acid, or heating at 120 C for 5 min. The organism Ae6 was strongly adhesive to rabbit intestines as well as human intestines, and agglutinated erythrocytes. Anti‐pili antibody (Fab fraction) did not block the adhesion. Purified Ae6‐R pili did not adhere to the intestine or to the erythrocytes. However, the anti‐pili Fab inhibited pellicle formation of the organisms cultured in broth, and also inhibited salt agglutination with ammonium sulfate. From these results, Ae6‐R pili are not likely a colonization factor but probably play a role in the autoaggregation of the organisms.