In vitro and in vivo activities of flexibacter maritimus toxins

Kusuda, R.

Reports of USA Marine Biology Institute. Kochi University 10(1): 1-8

1988


Accession: 007437625

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Abstract
In vitro and in vivo activities of lyophilized culture filtrate, precipitated extracellular product (ECP), protease, hemolysin, crude LPS, pure LPS and sonicated cell-free supernatant of Flexibacter maritimus were examined to see if they correlated with the pathogenicity of the bacteria in black sea bream, Acanthopagrus schlegeli, and red sea bream, Pagrus major, fry. Median lethal doses (LD50) following intraperitoneal injection in black sea bream were 26.5, 25.5, 31.0 and 123.mu.g/fish in hemolysin, ECP, sonicated cell-free supernatant and lyophilized culture filtrate respectively. Black sea bream showed lower LD50 values than red sea beam. No mortalities were observed in crude LPS, pure LPS and protease-injected groups, but protease and crude LPS produced 40% mortality when administered together. Mortalities and moribund fish in the ECP and hemolysin-injected groups commonly showed serious fluid in the body cavity, hypertrophied spleen, petechial hemorrhages in the visceral fat and intestines, and suppurated liver. These gross pathological signs were not produced by the other toxin preparations. The pathogenicity of F. maritimus in black sea bream and red sea bream fry may be attributed to ECP and hemolysin although it was not confirmed that these fractions were directly responsible for pathogenicity. Their rather insignificant in vitro activities could not be clearly correlated with their toxic effects in vivo. It is suggested that the bacteria may exert pathogenicity by the synergistic interaction of the toxins and enzymes examined.