Plasmid and serological differences between Edwardsiella ictaluri strains

Area of Science:

• Bacteriology
• Aquaculture
• Molecular Biology

Background:

• Edwardsiella ictaluri is a significant pathogen of channel catfish.
• Previous studies identified two cryptic plasmids (pCL1 and pCL2) in U.S. channel catfish isolates.
• These isolates were considered serologically homogeneous.

Purpose of the Study:

• To investigate plasmid content and serological characteristics of non-channel catfish Edwardsiella ictaluri isolates.
• To compare these isolates with those from channel catfish.

Main Methods:

• Plasmid profiling using gel electrophoresis.
• Serological analysis including polyclonal antiserum reactions (surface fluorescence, agglutination).
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting of cell extracts.

Main Results:

• A danio isolate shared plasmids similar to pCL1 and pCL2 and was serologically indistinguishable from channel catfish isolates.
• A green knife fish (GNF) isolate possessed four plasmids, with two hybridizing to pCL1 and pCL2 probes.
• The GNF isolate was serologically distinct, with unique O antigen, despite similar protein banding patterns.

Conclusions:

• Edwardsiella ictaluri exhibits distinct serotypes beyond those found in channel catfish.
• Plasmid and serological analyses are valuable tools for detecting emerging, structurally distinct E. ictaluri strains in aquaculture.