Md. Pearson et al., Virulence properties of motile aeromonads isolated from farmed frogs Rana tigerina and R. rugulosa, DIS AQU ORG, 40(3), 2000, pp. 185-193
Virulence factors were compared in Aeromonas species isolated from clinical
ly normal and septicaemic farmed frogs from Thailand. Haemolysin activities
against frog erythrocytes were significantly different within the collecti
on of aeromonads. Groups of high haemolytic activity (unspeciated Aeromonas
, Au), moderate haemolytic activity (A, hydrophila), and low haemolytic act
ivity (A. veronii biovar sobria, A. veronii biovar veronii, A. caviae, A. s
chubertii) were noted. DNA colony hybridisation studies revealed that Au is
olates possessed a haemolysin gene (ASH1) which was not present in any of t
he other Thai aeromonads or type strains tested. Elastinolytic activity was
demonstrated in 90% of the Au isolates, 60% of the A. hydrophila isolates
and in none of the other motile aeromonads. The cytotoxic activity of the A
eromonas isolates varied according to the source of cells used in the assay
s. Cells from rainbow trout were extremely sensitive to Au toxins but less
so to toxins produced by other species. In contrast mammalian cells showed
very little sensitivity to Au toxins but were more sensitive to toxins prod
uced by A. hydrophila. Selection of suitable assay substrates is therefore
important.