MEASUREMENT OF VIRULENCE OF AEROMONADS USING A SUCKLING MOUSE MODEL OF INFECTION

Virulent and avirulent strains of Aeromonas spp. were identified and v irulence quantified using an animal model. Virulence was measured by d etermining a 50% lethal dose (LD(50)) 43 h after oral administration o f live bacteria. The LD(50) of virulent Aeromonas isolates ranged from log(10) 7.53 (mean) organisms to log(10) 8.88 (mean). Some isolates w ere avirulent in this model. Detection of cytotoxic activity in cultur e supernatants correlated with virulence (Fisher exact test, P = 0.002 9). There was no correlation between LD(50) and the source of the isol ate, beta-haemolysis or lipopolysaccharide (LPS) banding profile on SD S-PAGE. In this animal model, virulence was multifactorial in that: (i ) bacterial multiplication in the gut was associated with fatal infect ion; (ii) the increase in bacterial numbers in the gut of mice adminis tered a lethal dose of bacteria was accompanied by accumulation of flu id; and (iii) there was evidence of extraintestinal spread of infectio n. Protection of suckling mice by rabbit antiserum to Aeromonas cell e nvelopes was observed.