Abstract

AGUIRRE-GUZMAN, Gabriel et al. Proteinaceous exotoxins of shrimp-pathogenic isolates of Vibrio penaeicida and Vibrio nigripulchritudo. Cienc. mar [online]. 2003, vol.29, n.1, pp.77-88. ISSN 0185-3880.

The pathogenicity of two V. penaeicida strains, AM101 and KH-1, with different geographic origin, and V. nigripulchritudo strain AM102, were investigated in juvenile blue shrimp species Litopenaeus stylirostris. Alive bacteria and protein fractions (PFs) obtained from cell-free supernatants (CFS) were used in experimental challenges. Strains AM102, AM101, and KH-1 produced respectively 60, 54 and 12% mortality at 96 h after infection using 10⁴ cfu mL^-1 of bacterial suspension. Exocellular toxin-like factors were evidenced in CFS from the New Caledonian strains (AM102 and AM101) but not in the Japanese strain (KH-1). At 48 h post injection of each CFS, mortality rates were respectively 96, 98 and 5% when these strains were cultivated at 20°C, whereas only 0, 16 and 5% mortality rates were observed when these strains were cultivated at 30°C. Clear differences in pathogenicity between both V. penaeicida strains of distinct geographic origin (AM101 and KH-1) were thus emphasized. Protein fractions were obtained from CFS of all the strains tested in this study and cultivated at 20°C, by ammonium sulfate precipitation. Whatever the used strain, significantly higher mortalities were produced with PFs obtained with 0-l-0⁰/o of ammonium sulfate saturation, in respect to those produced with PFs60 and PFs80. Shrimp injected with PFs40 from strains AM102, AM101 and KH-1, and at a 20-µg org^-1 dose produced respectively 100, 90 and 60% mortality 46 h after the challenge. The strain AM101 showed a median lethal dose of approximately 5 µg protein org^-1 (1-1.25 µg protein g^-1 body weight) 59 h after injection. The PFs40 from New Caledonian strains were found sensitive to heating and proteinase K treatments, reinforcing thus the hypothesis of their proteinaceous nature. Surprisingly, PFs40 from each bacterial strain displayed similar protein bands by SDS-PAGE suggesting that the tested strains share a common exotoxic compound regardless their distinct geographic origin or species.

Keywords : Vibrio penaeicida; Vibrio nigripulchritudo; Litopenaeus stylirostris; shrimp; exotoxin; pathogenicity.

        · abstract in Spanish     · text in English     · English ( pdf )