title: Virulence of Aeromonas hydrophila to channel catfish Ictaluras punctatus fingerlings in the presence and absence of bacterial extracellular products.
abstract: We investigated the virulence of three 2009 west Alabama isolates of Aeromonas hydrophila (AL09-71, AL09-72 and AL09-73) to channel catfish Ictalurus punctatus fingerlings (4.6 +/- 1.3 g) in the presence and absence of extracellular products (ECPs) from overnight bacterial culture using both bath immersion and intraperitoneal injection routes. At a concentration of 1.65 x 10(8) colony-forming units (CFU) ml(-1), AL09-73 without its ECPs killed 100% of the catfish fingerlings within 2 h by bath immersion. However, at a similar concentration, AL09-73 in the presence of its ECPs killed only 23 +/- 6% catfish fingerlings. The absence of ECPs in the bath immersion experiment also significantly (p < 0.05) increased the virulence of AL09-71, AL09-72, and AL98-C1B, a 1998 Alabama strain of A. hydrophila, suggesting that the virulence of the 4 A. hydrophila isolates was mainly due to bacterial cells, not to their overnight ECPs. Filter-sterilized ECPs failed to kill any catfish by bath immersion or injection. The virulence order of the 4 A. hydrophila isolates, by both bath immersion and intraperitoneal injection, was: AL09-73 > or = AL09-71 > AL09-72 > or = AL98-C1B. At 2 h post bath immersion, all 4 isolates of A. hydrophila were found in all tissues studied (skin, intestine, liver, spleen, kidney, gill and brain), with the highest bacteria count being in the gill and kidney.
authors.affiliation: Aquatic Animal Health Research Unit, USDA-ARS, 990 Wire Road, Auburn, Alabama 36832, USA. julia.pridgeon@ars.usda.gov
authors.forename: Julia W
authors.initials: JW
authors.lastname: Pridgeon
authors.forename: Phillip H
authors.initials: PH
authors.lastname: Klesius
mesh_terms: D016980:Aeromonas hydrophila / Q000378:metabolism / Q000472:pathogenicity*; D000818:Animals; D005393:Fish Diseases / Q000382:microbiology*; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology / Q000662:veterinary*; D007059:Ictaluridae; D014774:Virulence