The role of a 40-megadalton plasmid in the adherence and hemolytic properties of Aeromonas hydrophila.

A cured strain of Aeromonas hydrophila, MS-2PC, was examined for phenotypic changes in antibiotic resistance, adherence, and hemolysis. Parental strain MS-2 was resistant to ampicillin, novobiocin, and carbenicillin; MS-2PC, which lacked a 40-MDa plasmid, was also resistant to ampicillin but was sensitive to novobiocin and carbenicillin. The adherence of these isolates to CaCo-2 and HeLa cells was examined. MS-2PC demonstrated greater attachment to both cell lines than did strain MS-2 (p < 0.05). MS-2PC also demonstrated greater hemolysis activity than did MS-2 (p < 0.01). The 40-Mda plasmid was isolated and reintroduced into MS-2PC. The resulting transformant, 20T, regained resistance to carbenicillin and novobiocin. The attachment ability of 20T was equal to that of MS-2, and both strains demonstrated significantly lower attachment ability than that of MS-2PC (p < 0.01). Strains MS-2 and 20T exhibited the same hemolysis pattern, which was markedly less than that of strain MS-2PC. These results indicate that the 40-Mda plasmid which codes for antibiotic resistance also controls other functions of A. hydrophila MS-2.