ARS | Publication request: Attenuation of a virulent Aeromonas hydrophila with novobiocin and pathogenic characterization of the novobiocin-resistant strain

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 25, 2012
Publication Date: December 12, 2012
Citation: Wei Pridgeon, Y., Aksoy, M., Klesius, P.H., Srivastavae, K., Reddy, G. 2012. Attenuation of a virulent Aeromonas hydrophila with novobiocin and pathogenic characterization of the novobiocin-resistant strain. Journal of Applied Microbiology. 113:1319-1328.

Interpretive Summary: A novobiocin-resistant strain of bacterium Aeromonas hydrophila was obtained from a virulent Aeromonas hydrophila strain AH11P through selection of resistance to novobiocin. The novobiocin-resistance strain was named AH11NOVO. AH11NOVO was found to be not virulent to channel catfish, but AH11P was highly virulent to channel catfish. When AH11NOVO vaccinated channel fish were challenged with AH11P at 14 days post vaccination, the relative percent of survival of vaccinated fish was 100%. AH11NOVO was found to have smaller growth rate than AH11P. In addition, AH11NOVO was not motile. Furthermore, AH11NOVO was found to be less able to invade to catfish gill cells than AH11P. The lower invasion rate of AH11NOVO might explain why it was not virulent to channel catfish.

Technical Abstract: A novobiocin-resistant strain AH11NOVO was obtained from a virulent A. hydrophila strain AH11P through selection of resistance to novobiocin. AH11NOVO was found to be avirulent to channel catfish whereas AH11P was virulent. When AH11NOVO vaccinated channel catfish were challenged with AH11P at 14 days post vaccination, relative percent of survival of vaccinated fish was 100%. The cell proliferation rate of AH11NOVO was found to be significantly (P<0.05) smaller than that of AH11P. In vitro motility assay revealed that AH11NOVO was immotile whereas AH11P was motile. AH11NOVO was also found to have significantly (P<0.05) lower in vitro chemotactic response to catfish mucus than that of AH11P. Although the ability of AH11NOVO to attach catfish gill cells was found to be similar to that of AH11P, the ability of AH11NOVO to invade catfish gill cells was found to be significantly (P<0.05) lower than that of AH11P. The significantly lower chemotactic response and invasion ability of AH11NOVO compared to that of its virulent parent strain AH11P might shed light on the pathogenesis of A. hydrophila.