The effect of cutaneous injury on a reproducible immersion challenge model for Flavobacterium columnare infection in channel catfish (Ictalurus punctatus)

We evaluated four methods of acute cutaneous injury: physical abrasion, hot and cold branding, and chemical scalds, to predispose channel catfish (Ictalurus punctatus) to columnaris disease, caused by the bacterium Flavobacterium columnare. Only physical abrasion (PA) and hot branding (HB) produced lasting alterations of epithelial architecture. Immersion challenge of PA or HB fish 10(8) cfu/ml virulent F columnare at 29 +/- 2 degrees C immediately after treatment resulted in death of most fish within the first 48 h. Immersion challenge 24 h after cutaneous injury resulted in 60% mortality with PA and 2% in HB. Cutaneous injury 48-72 h before challenge did not result in significant mortality. We quantified and modeled the median 96 h LD50 for PA and HB. The 96 h LD50 for abrasion (10(4 3 +/- 0 3) cfu/ml) was a log lower than for branded fish (10(5.0 +/- 0.4) cfu/ml). The LD50 for HB plus AS was 10(5 8 +/- 0.3) cfu/ml, a log higher than for HB fish without Stresscoat(TM), an artificial slime agent (AS). Hot branding produced more consistent infection in terms of 96 h LD50s. Induction of experimental columnaris was dependent on the length of time between injury and pathogen exposure (<4 h), size of area disrupted on the epidermis, and dose of bacteria. A significant reduction in mortality and delay in death were noted when abraded fish were treated with AS and immediately challenged, suggesting that columnaris disease may be minimized or prevented by protecting a wounded catfish with AS, thus confirming the relationship of pathogenesis of F columnare entering a wound. (C) 2005 Elsevier B.V. All rights reserved.