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Title: Molecular identfication and virulence of three Aeromonas hydrophila isolates cultured from infected channel catfish during a disease outbreak in West Alabama (USA) in 2009

Author
item Wei Pridgeon, Yuping
item Klesius, Phillip

Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2011
Publication Date: 5/9/2011
Citation: Wei Pridgeon, Y., Klesius, P.H. 2011. Molecular identfication and virulence of three Aeromonas hydrophila isolates cultured from infected channel catfish during a disease outbreak in West Alabama (USA) in 2009. Diseases of Aquatic Organisms. 94:249-253.

Interpretive Summary: Three isolates of Aeromonas hydrophila were cultured from infected channel catfish during a disease outbreak in West Alabama in August 2009. Sequence analysis of four genes of the three strains revealed that the three strains were closely related to each other, sharing 97 to 99% nucleotide sequence similarities. However, gene sequences of the three 2009 isolates shared much lower homology with a 1998 Alabama isolate of Aeromonas hydrophila, suggesting that the three 2009 isolates were different from the 1998 Alabama isolate of Aeromonas. Virulence studies revealed that the virulence of the three 2009 isolates was not significantly different from each other. However, the three 2009 isolates were significantly more virulent than the 1998 Alabama isolate, suggesting that the three 2009 isolates of A. hydrophila were highly virulent to channel catfish.

Technical Abstract: Three isolates (AL09-71, AL09-72, and AL09-73) of Aeromonas hydrophila were cultured from infected channel catfish during a disease outbreak in West Alabama in August 2009. Sequence analysis of 16S-23S rDNA intergenic spacer region (ISR), cpn60, gyrB, and rpoD genes of the three strains revealed that the three strains were closely related to each other, sharing 97 to 99% nucleotide sequence similarities. However, ISR sequences of the three 2009 isolates shared only 64% nucleotide sequences with AL98-C1B, a 1998 isolate from diseased fish in Alabama, although sequences of cpn60, gyrB, and rpoD sequences of the three 2009 isolates shared 91 to 95% homologies with AL98-C1B. Virulence studies revealed that the LD50 values of the three 2009 isolates were significantly lower than that of AL98-C1B. Based on LD95 values, the virulence of the three 2009 isolates was not significantly different from each other. However, the LD95 values of the three 2009 isolates were significantly lower than that of AL98-C1B, suggesting that the three 2009 isolates of A. hydrophila were highly virulent to channel catfish.