title: Electrostatic mechanism of survival of virulent Aeromonas salmonicida strains in river water.
abstract: The ecological mechanism of survival of Aeromonas salmonicida, the bacterial pathogen of fish furunculosis, in river water was investigated by laboratory-based experiments with two virulent strains (which were autoagglutinating) and two virulent strains (which were nonagglutinating). A difference in net electrical charge of A. salmonicida cells was detected by electrophoresis; cells of the virulent strains were negative, whereas cells of the avirulent strains were positive. Despite the loss of viable cells within a week in distilled water and physiological saline (0.85% sodium chloride), the cells of the virulent strains survived for more than 15 weeks in the presence of diluted humic acid (10 micrograms/ml), tryptone (10 micrograms/ml), and cleaned river sand (100 g/100 ml of medium), but loss of viable cells occurred within 5 weeks in the absence of sand. The cells of the avirulent strains lost viability within 2 weeks with no relation to the presence of sand. Using ion-exchange columns, humic acid and the amino acids of tryptone were found to be anionic and cationic in water (pH 7.0), respectively. Sand particles had a high capacity to adsorb humic acid alone and amino acid-humic acid complexes. Thirty to fifty times the environmental concentration of amino acids (10 micrograms/ml) were accumulated on the surface of sand particles, thereby permitting only bacterial cells carrying net negative electrical charges (virulent cells) to survive for a long period on the surface of the sand particles. These electrostatic interrelationships among river sand, humic acid, and bacterial cells are closely implicated in the mechanism of long-term survival of virulent A. salmonicida in river sediments.
mesh_terms: D000327:Adsorption; D000333:Aeromonas / Q000254:growth & development* / Q000472:pathogenicity; D000371:Agglutination; D000818:Animals; D002850:Chromatography, Gel; D003470:Culture Media; D004463:Ecology; D004560:Electricity; D005618:Fresh Water; D006812:Humic Substances / Q000494:pharmacology; D007474:Ion Exchange; D010461:Peptones / Q000494:pharmacology; D014337:Trout / Q000382:microbiology; D014871:Water Microbiology
chemical_list: D003470:Culture Media; D006812:Humic Substances; D010461:Peptones; C001830:tryptones