title: Enhanced susceptibility of channel catfish to the bacterium Edwardsiella ictaluri after parasitism by Ichthyophthirius multifiliis.
abstract: Bacterium Edwardsiella ictaluri and parasite Ichthyophthirius multifiliis (Ich) are two common pathogens of cultured fish. The objective of this study was to evaluate the susceptibility of channel catfish Ictalurus punctatus to E. ictaluri and determine bacterial loads in different fish organs after parasitism by Ich. Fish received the following treatments: (1) infected by I. multifiliis at 5000 theronts/fish and exposed to E. ictaluri; (2) infected by I. multifiliis alone; (3) exposed to E. ictaluri alone; and (4) non-infected control. E. ictaluri in fish organs were quantified by quantitative real-time polymerase chain reaction and reported as genome equivalents per mg of tissue (GEs/mg). The results demonstrated that the Ich-parasitized catfish showed significantly (P<0.05) higher mortality (91.7%) when exposed to E. ictaluri than non-parasitized fish (10%). The bacterial loads in fish infected by 5000 theronts/fish ranged from 6497 to 163,898 GEs/mg which was between 40 and 2000 fold higher than non-parasitized fish (49-141 GEs/mg). Ich infection enhanced the susceptibility of channel catfish to bacterial invasion and increased fish mortality.
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Aquatic Animal Health Research Unit, 990 Wire Road, Auburn, AL 36832, USA. dehai.xu@ars.usda.gov
authors.forename: De-Hai
authors.initials: DH
authors.lastname: Xu
authors.forename: Craig A
authors.initials: CA
authors.lastname: Shoemaker
authors.forename: Maurício L
authors.initials: ML
authors.lastname: Martins
authors.forename: Julia W
authors.initials: JW
authors.lastname: Pridgeon
authors.forename: Phillip H
authors.initials: PH
authors.lastname: Klesius
mesh_terms: D000818:Animals; D058491:Bacterial Load; D016770:Ciliophora Infections / Q000382:microbiology / Q000469:parasitology / Q000662:veterinary*; D060085:Coinfection / Q000662:veterinary*; D020610:Edwardsiella ictaluri / Q000502:physiology*; D004756:Enterobacteriaceae Infections / Q000382:microbiology / Q000469:parasitology / Q000662:veterinary*; D005393:Fish Diseases / Q000382:microbiology* / Q000469:parasitology*; D016803:Hymenostomatida / Q000502:physiology*; D007059:Ictaluridae; D060888:Real-Time Polymerase Chain Reaction